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Re: [PATCH V7 3/3] dma: add Qualcomm Technologies HIDMA channel driver

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  Re: [PATCH V7 3/3] dma: add Qualcomm Technologies HIDMA channel  driver Sinan Kaya <okaya@codeaurora.org> - 2015-11-30 21:10 +0100
    Re: [PATCH V7 3/3] dma: add Qualcomm Technologies HIDMA channel  driver Vinod Koul <vinod.koul@intel.com> - 2015-12-01 12:40 +0100
      Re: [PATCH V7 3/3] dma: add Qualcomm Technologies HIDMA channel  driver Sinan Kaya <okaya@codeaurora.org> - 2015-12-01 22:20 +0100
        Re: [PATCH V7 3/3] dma: add Qualcomm Technologies HIDMA channel  driver Sinan Kaya <okaya@codeaurora.org> - 2015-12-02 20:10 +0100
          Re: [PATCH V7 3/3] dma: add Qualcomm Technologies HIDMA channel  driver Vinod Koul <vinod.koul@intel.com> - 2015-12-05 09:00 +0100
            Re: [PATCH V7 3/3] dma: add Qualcomm Technologies HIDMA channel  driver Sinan Kaya <okaya@codeaurora.org> - 2015-12-08 15:40 +0100
            Re: [PATCH V7 3/3] dma: add Qualcomm Technologies HIDMA channel  driver Sinan Kaya <okaya@codeaurora.org> - 2015-12-10 21:20 +0100
              Re: [PATCH V7 3/3] dma: add Qualcomm Technologies HIDMA channel  driver Vinod Koul <vinod.koul@intel.com> - 2015-12-11 10:40 +0100

#1280244 — Re: [PATCH V7 3/3] dma: add Qualcomm Technologies HIDMA channel driver

On 11/30/2015 3:59 AM, Vinod Koul wrote:
> On Sun, Nov 22, 2015 at 09:28:25PM -0500, Sinan Kaya wrote:
>> This patch adds support for hidma engine. The driver consists
>> of two logical blocks. The DMA engine interface and the
>> low-level interface. The hardware only supports memcpy/memset
>> and this driver only support memcpy interface. HW and driver
>> doesn't support slave interface.
>>
>> Signed-off-by: Sinan Kaya <okaya@codeaurora.org>
>> ---
>>  .../devicetree/bindings/dma/qcom_hidma.txt         |  18 +
>>  drivers/dma/qcom/Kconfig                           |  10 +
>>  drivers/dma/qcom/Makefile                          |   2 +
>>  drivers/dma/qcom/hidma.c                           | 706 ++++++++++++++++
>>  drivers/dma/qcom/hidma.h                           | 157 ++++
>>  drivers/dma/qcom/hidma_dbg.c                       | 217 +++++
>>  drivers/dma/qcom/hidma_ll.c                        | 924 +++++++++++++++++++++
>>  7 files changed, 2034 insertions(+)
> 
> This was one of the reasons for slow review of this. I started few times but
> large patches made this getting pushed back
> 
> Pls help reviewers by splitting your code which looking at this could have
> been done

I have split the debugfs support from this patch to its own patch. Any
other idea on how else you'd break the code? I can take one more step
and separate the lower layer from the OS layer by using stub functions
on the initial commit.

> 
>> +#include <linux/dmaengine.h>
>> +#include <linux/dma-mapping.h>
>> +#include <linux/err.h>
>> +#include <linux/init.h>
>> +#include <linux/interrupt.h>
>> +#include <linux/list.h>
>> +#include <linux/module.h>
>> +#include <linux/platform_device.h>
>> +#include <linux/slab.h>
>> +#include <linux/spinlock.h>
>> +#include <linux/of_dma.h>
>> +#include <linux/property.h>
>> +#include <linux/delay.h>
>> +#include <linux/highmem.h>
>> +#include <linux/io.h>
>> +#include <linux/sched.h>
>> +#include <linux/wait.h>
>> +#include <linux/acpi.h>
>> +#include <linux/irq.h>
>> +#include <linux/atomic.h>
>> +#include <linux/pm_runtime.h>
> 
> Do you need so many headers...?

probably not, let me see what I can do about them.

> 
>> +MODULE_PARM_DESC(event_channel_idx,
>> +		"event channel index array for the notifications");
> 
> Can you explain this parameter in detail pls

OK. I added the following comment to the code.

/*
 * Each DMA channel is associated with an event channel for interrupt
 * delivery. The event channel index usually comes from the firmware through
 * ACPI/DT. When a HIDMA channel is executed in the guest machine
context (QEMU)
 * the device tree gets auto-generated based on the memory and IRQ resources
 * this driver uses on the host machine. Any device specific parameter
such as
 * event-channel gets ignored by the QEMU.
 * We are using this command line parameter to pass the event channel
index to
 * the guest machine.
 */
s

> 
>> +static void hidma_callback(void *data)
>> +{
>> +	struct hidma_desc *mdesc = data;
>> +	struct hidma_chan *mchan = to_hidma_chan(mdesc->desc.chan);
>> +	struct dma_device *ddev = mchan->chan.device;
>> +	struct hidma_dev *dmadev = to_hidma_dev(ddev);
>> +	unsigned long irqflags;
>> +	bool queued = false;
>> +
>> +	spin_lock_irqsave(&mchan->lock, irqflags);
>> +	if (mdesc->node.next) {
>> +		/* Delete from the active list, add to completed list */
>> +		list_move_tail(&mdesc->node, &mchan->completed);
>> +		queued = true;
>> +	}
>> +	spin_unlock_irqrestore(&mchan->lock, irqflags);
>> +
>> +	hidma_process_completed(dmadev);
>> +
>> +	if (queued) {
>> +		pm_runtime_mark_last_busy(dmadev->ddev.dev);
>> +		pm_runtime_put_autosuspend(dmadev->ddev.dev);
>> +	}
>> +}
> 
> Callback is typically referred to client callback upon dma completion, can
> you explain what you are trying to do here

When a DMA transfer completes, the hidma_callback function in the
hidma.c file gets called from the lower layer (hidma_ll.c) in order to
move this request from active queue into the completed queue.

hidma_process_completed eventually calls the "client callback" in it.

The PM stuff is for guaranteeing that clocks are not turned off while HW
is working on it.

I grab the PM lock in issue pending and release it in the hidma_callback.

> 
>> +static int hidma_chan_init(struct hidma_dev *dmadev, u32 dma_sig)
>> +{
>> +	struct hidma_chan *mchan;
>> +	struct dma_device *ddev;
>> +
>> +	mchan = devm_kzalloc(dmadev->ddev.dev, sizeof(*mchan), GFP_KERNEL);
>> +	if (!mchan)
>> +		return -ENOMEM;
>> +
>> +	ddev = &dmadev->ddev;
>> +	mchan->dma_sig = dma_sig;
>> +	mchan->dmadev = dmadev;
>> +	mchan->chan.device = ddev;
>> +	dma_cookie_init(&mchan->chan);
>> +
>> +	INIT_LIST_HEAD(&mchan->free);
>> +	INIT_LIST_HEAD(&mchan->prepared);
>> +	INIT_LIST_HEAD(&mchan->active);
>> +	INIT_LIST_HEAD(&mchan->completed);
>> +
>> +	spin_lock_init(&mchan->lock);
>> +	list_add_tail(&mchan->chan.device_node, &ddev->channels);
>> +	dmadev->ddev.chancnt++;
> 
> Have you looked at vchan implementation and moving list handling to this
> layer ?

I'll add vchan support later on another revision. The original code had
vchan support in it. It became a terminology mess. So, I removed it for
the moment.

Using vchan, I can take multiple clients and serve them in a single
channel later.

> 
>> +	return 0;
>> +}
>> +
>> +static void hidma_issue_pending(struct dma_chan *dmach)
>> +{
>> +	struct hidma_chan *mchan = to_hidma_chan(dmach);
>> +	struct hidma_dev *dmadev = mchan->dmadev;
>> +
>> +	/* PM will be released in hidma_callback function. */
>> +	pm_runtime_get_sync(dmadev->ddev.dev);
> 
> Oh no, this is not allowed. pm_runtime_get_sync() can sleep and
> issue_pending can be invoked from atomic context.

OK. I didn't know that. I'll try pm_runtime_get first. If it fails, I'll
post a task to do the real job with pm_runtime_get_sync.

The clocks may be off by the time the request is made. I need to grab
the PM lock before accessing the HW registers.

> 
>> +static enum dma_status hidma_tx_status(struct dma_chan *dmach,
>> +			dma_cookie_t cookie, struct dma_tx_state *txstate)
>> +{
>> +	struct hidma_chan *mchan = to_hidma_chan(dmach);
>> +	enum dma_status ret;
>> +
>> +	if (mchan->paused)
>> +		ret = DMA_PAUSED;
> 
> This is not quite right. The status query is for a descriptor and NOT for
> channel. Here if the descriptor queried was running then it would be paused
> for the rest pending txn, it would be DMA_IN_PROGRESS.

The channel can be paused by the hypervisor. If it is paused, then no
other transaction will go through including the pending requests. That's
why, I'm checking the state first.

> 
>> +static dma_cookie_t hidma_tx_submit(struct dma_async_tx_descriptor *txd)
>> +{
>> +	struct hidma_chan *mchan = to_hidma_chan(txd->chan);
>> +	struct hidma_dev *dmadev = mchan->dmadev;
>> +	struct hidma_desc *mdesc;
>> +	unsigned long irqflags;
>> +	dma_cookie_t cookie;
>> +
>> +	if (!hidma_ll_isenabled(dmadev->lldev))
>> +		return -ENODEV;
> 
> is this not too late for this check, you should fail this on prepare
> method

The channels can be paused by the hypervisor at runtime after the guest
OS boot. The client might have allocated the channels during guest
machine boot. If a channel is paused and client makes a request, client
will never get the callback. By placing this check, I'm looking at the
runtime status of the channel and rejecting the transmit request right
ahead.

> 
> 
>> +static int hidma_alloc_chan_resources(struct dma_chan *dmach)
>> +{
>> +	struct hidma_chan *mchan = to_hidma_chan(dmach);
>> +	struct hidma_dev *dmadev = mchan->dmadev;
>> +	struct hidma_desc *mdesc, *tmp;
>> +	unsigned long irqflags;
>> +	LIST_HEAD(descs);
>> +	unsigned int i;
>> +	int rc = 0;
>> +
>> +	if (mchan->allocated)
>> +		return 0;
>> +
>> +	/* Alloc descriptors for this channel */
>> +	for (i = 0; i < dmadev->nr_descriptors; i++) {
>> +		mdesc = kzalloc(sizeof(struct hidma_desc), GFP_KERNEL);
> 
> GFP_NOWAIT pls, this can be called from atomic context

I'll change it, but why would anyone allocate a channel in an interrupt
handler?

> 
>> +		if (!mdesc) {
>> +			rc = -ENOMEM;
>> +			break;
>> +		}
>> +		dma_async_tx_descriptor_init(&mdesc->desc, dmach);
>> +		mdesc->desc.flags = DMA_CTRL_ACK;
> 
> what is the purpose of setting this flag here

It means that the code only supports interrupt. Maybe, you can correct
me here. I couldn't see a very useful info about the DMA engine flags.
My understanding is that DMA_CTRL_ACK means user wants an interrupt
based callback.

If DMA_CTRL_ACK is not specified, then user wants to poll for the
results. The current code only supports the interrupt based delivery for
callbacks. Polling support is another to-do in my list for small sized
transfers.

> 
>> +static void hidma_free_chan_resources(struct dma_chan *dmach)
>> +{
>> +	struct hidma_chan *mchan = to_hidma_chan(dmach);
>> +	struct hidma_dev *mdma = mchan->dmadev;
>> +	struct hidma_desc *mdesc, *tmp;
>> +	unsigned long irqflags;
>> +	LIST_HEAD(descs);
>> +
>> +	if (!list_empty(&mchan->prepared) || !list_empty(&mchan->active) ||
>> +		!list_empty(&mchan->completed)) {
>> +		/*
>> +		 * We have unfinished requests waiting.
>> +		 * Terminate the request from the hardware.
> 
> that sounds as bug.. free should be called when txn are completed/aborted

Let me see what other drivers are doing...

> 
>> +		 */
>> +		hidma_cleanup_pending_tre(mdma->lldev, ERR_INFO_SW,
>> +					ERR_CODE_UNEXPECTED_TERMINATE);
>> +
>> +		/* Give enough time for completions to be called. */
>> +		msleep(100);
> 
> should we not poll/read after delay, also we are still in atomic context
> 
>> +	}
>> +
>> +	spin_lock_irqsave(&mchan->lock, irqflags);
>> +	/* Channel must be idle */
> 
> sorry I do not like that assumption
> 
>> +	/* return all user requests */
>> +	list_for_each_entry_safe(mdesc, tmp, &list, node) {
>> +		struct dma_async_tx_descriptor *txd = &mdesc->desc;
>> +		dma_async_tx_callback callback = mdesc->desc.callback;
>> +		void *param = mdesc->desc.callback_param;
>> +		enum dma_status status;
>> +
>> +		dma_descriptor_unmap(txd);
>> +
>> +		status = hidma_ll_status(dmadev->lldev, mdesc->tre_ch);
>> +		/*
>> +		 * The API requires that no submissions are done from a
>> +		 * callback, so we don't need to drop the lock here
>> +		 */
> 
> That is correct assumption for async_tx and which is deprecated now.
> In fact the converse is true for rest!

I copied this function from another driver. The cookie/unmap business
seemed scary to me. Can you point me to a good/recent implementation if
this is deprecated?

> 
>> +static int hidma_pause(struct dma_chan *chan)
>> +{
>> +	struct hidma_chan *mchan;
>> +	struct hidma_dev *dmadev;
>> +
>> +	mchan = to_hidma_chan(chan);
>> +	dmadev = to_hidma_dev(mchan->chan.device);
>> +	if (!mchan->paused) {
>> +		pm_runtime_get_sync(dmadev->ddev.dev);
>> +		if (hidma_ll_pause(dmadev->lldev))
>> +			dev_warn(dmadev->ddev.dev, "channel did not stop\n");
>> +		mchan->paused = true;
>> +		pm_runtime_mark_last_busy(dmadev->ddev.dev);
>> +		pm_runtime_put_autosuspend(dmadev->ddev.dev);
>> +	}
>> +	return 0;
>> +}
> 
> This is interesting, we associate pause/resume for slave dma ops and not for
> memcpy ops, what is the reason for adding pause/resume here?

Why is it limited to the slave device only? I can queue a bunch of
requests. I can pause and resume their execution with the current
implementation.

> 
>> +static int hidma_remove(struct platform_device *pdev)
>> +{
>> +	struct hidma_dev *dmadev = platform_get_drvdata(pdev);
>> +
>> +	pm_runtime_get_sync(dmadev->ddev.dev);
>> +	dma_async_device_unregister(&dmadev->ddev);
>> +	hidma_debug_uninit(dmadev);
>> +	hidma_ll_uninit(dmadev->lldev);
>> +	hidma_free(dmadev);
>> +
>> +	dev_info(&pdev->dev, "HI-DMA engine removed\n");
>> +	pm_runtime_put_sync_suspend(&pdev->dev);
>> +	pm_runtime_disable(&pdev->dev);
> 
> and your irq is still active and can invoke your irq handler!
> 

why? I shutdown the IRQ in hidma_ll_uninit and request the interrupt
with devm_request_irq. As soon as this driver is removed, the interrupt
should be released by the managed code.

>> +
>> +	return 0;
>> +}
>> +
>> +#if IS_ENABLED(CONFIG_ACPI)
>> +static const struct acpi_device_id hidma_acpi_ids[] = {
>> +	{"QCOM8061"},
> Qcom and ACPI, that is v interesting combination !
> 
> 

Thanks for the detailed review.


-- 
Sinan Kaya
Qualcomm Technologies, Inc. on behalf of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a
Linux Foundation Collaborative Project
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#1280800

On Mon, Nov 30, 2015 at 03:06:36PM -0500, Sinan Kaya wrote:
> I have split the debugfs support from this patch to its own patch. Any
> other idea on how else you'd break the code? I can take one more step
> and separate the lower layer from the OS layer by using stub functions
> on the initial commit.

Yes the ll.c can be a separate patch and no need to add placeholders as
makefile can be last

> > 
> >> +static enum dma_status hidma_tx_status(struct dma_chan *dmach,
> >> +			dma_cookie_t cookie, struct dma_tx_state *txstate)
> >> +{
> >> +	struct hidma_chan *mchan = to_hidma_chan(dmach);
> >> +	enum dma_status ret;
> >> +
> >> +	if (mchan->paused)
> >> +		ret = DMA_PAUSED;
> > 
> > This is not quite right. The status query is for a descriptor and NOT for
> > channel. Here if the descriptor queried was running then it would be paused
> > for the rest pending txn, it would be DMA_IN_PROGRESS.
> 
> The channel can be paused by the hypervisor. If it is paused, then no
> other transaction will go through including the pending requests. That's
> why, I'm checking the state first.

You are missing the point. Channel can be paused, yes but the descriptor
is in queue and is not paused. The descriptor running is paused, yes.
There is subtle difference between these

> >> +static dma_cookie_t hidma_tx_submit(struct dma_async_tx_descriptor *txd)
> >> +{
> >> +	struct hidma_chan *mchan = to_hidma_chan(txd->chan);
> >> +	struct hidma_dev *dmadev = mchan->dmadev;
> >> +	struct hidma_desc *mdesc;
> >> +	unsigned long irqflags;
> >> +	dma_cookie_t cookie;
> >> +
> >> +	if (!hidma_ll_isenabled(dmadev->lldev))
> >> +		return -ENODEV;
> > 
> > is this not too late for this check, you should fail this on prepare
> > method
> 
> The channels can be paused by the hypervisor at runtime after the guest
> OS boot. The client might have allocated the channels during guest
> machine boot. If a channel is paused and client makes a request, client
> will never get the callback. By placing this check, I'm looking at the
> runtime status of the channel and rejecting the transmit request right
> ahead.

In this case you have request already given to you, here the request is
submitted to the pending queue, if hypervisor has paused you, so the entire
txn queue is paused. But from API semantics I would argue that this should be
accepted and suffer the same fate as already submitted txns

> 
> > 
> > 
> >> +static int hidma_alloc_chan_resources(struct dma_chan *dmach)
> >> +{
> >> +	struct hidma_chan *mchan = to_hidma_chan(dmach);
> >> +	struct hidma_dev *dmadev = mchan->dmadev;
> >> +	struct hidma_desc *mdesc, *tmp;
> >> +	unsigned long irqflags;
> >> +	LIST_HEAD(descs);
> >> +	unsigned int i;
> >> +	int rc = 0;
> >> +
> >> +	if (mchan->allocated)
> >> +		return 0;
> >> +
> >> +	/* Alloc descriptors for this channel */
> >> +	for (i = 0; i < dmadev->nr_descriptors; i++) {
> >> +		mdesc = kzalloc(sizeof(struct hidma_desc), GFP_KERNEL);
> > 
> > GFP_NOWAIT pls, this can be called from atomic context
> 
> I'll change it, but why would anyone allocate a channel in an interrupt
> handler?

remember this is dmaengine, where people traditionally wanted to offload
from cpu and were not allowed to sleep.

I think am okay with this one..

> 
> > 
> >> +		if (!mdesc) {
> >> +			rc = -ENOMEM;
> >> +			break;
> >> +		}
> >> +		dma_async_tx_descriptor_init(&mdesc->desc, dmach);
> >> +		mdesc->desc.flags = DMA_CTRL_ACK;
> > 
> > what is the purpose of setting this flag here
> 
> It means that the code only supports interrupt. Maybe, you can correct
> me here. I couldn't see a very useful info about the DMA engine flags.
> My understanding is that DMA_CTRL_ACK means user wants an interrupt
> based callback.

Right user wants, you are not user though

> 
> If DMA_CTRL_ACK is not specified, then user wants to poll for the
> results. The current code only supports the interrupt based delivery for
> callbacks. Polling support is another to-do in my list for small sized
> transfers.

See the documentation for flags and usage. The point here is that user
should set this. I know some old driver do this but that is not right

> 
> > 
> >> +static void hidma_free_chan_resources(struct dma_chan *dmach)
> >> +{
> >> +	struct hidma_chan *mchan = to_hidma_chan(dmach);
> >> +	struct hidma_dev *mdma = mchan->dmadev;
> >> +	struct hidma_desc *mdesc, *tmp;
> >> +	unsigned long irqflags;
> >> +	LIST_HEAD(descs);
> >> +
> >> +	if (!list_empty(&mchan->prepared) || !list_empty(&mchan->active) ||
> >> +		!list_empty(&mchan->completed)) {
> >> +		/*
> >> +		 * We have unfinished requests waiting.
> >> +		 * Terminate the request from the hardware.
> > 
> > that sounds as bug.. free should be called when txn are completed/aborted
> 
> Let me see what other drivers are doing...
> 
> > 
> >> +		 */
> >> +		hidma_cleanup_pending_tre(mdma->lldev, ERR_INFO_SW,
> >> +					ERR_CODE_UNEXPECTED_TERMINATE);
> >> +
> >> +		/* Give enough time for completions to be called. */
> >> +		msleep(100);
> > 
> > should we not poll/read after delay, also we are still in atomic context
> > 
> >> +	}
> >> +
> >> +	spin_lock_irqsave(&mchan->lock, irqflags);
> >> +	/* Channel must be idle */
> > 
> > sorry I do not like that assumption
> > 
> >> +	/* return all user requests */
> >> +	list_for_each_entry_safe(mdesc, tmp, &list, node) {
> >> +		struct dma_async_tx_descriptor *txd = &mdesc->desc;
> >> +		dma_async_tx_callback callback = mdesc->desc.callback;
> >> +		void *param = mdesc->desc.callback_param;
> >> +		enum dma_status status;
> >> +
> >> +		dma_descriptor_unmap(txd);
> >> +
> >> +		status = hidma_ll_status(dmadev->lldev, mdesc->tre_ch);
> >> +		/*
> >> +		 * The API requires that no submissions are done from a
> >> +		 * callback, so we don't need to drop the lock here
> >> +		 */
> > 
> > That is correct assumption for async_tx and which is deprecated now.
> > In fact the converse is true for rest!
> 
> I copied this function from another driver. The cookie/unmap business
> seemed scary to me. Can you point me to a good/recent implementation if
> this is deprecated?


> 
> > 
> >> +static int hidma_pause(struct dma_chan *chan)
> >> +{
> >> +	struct hidma_chan *mchan;
> >> +	struct hidma_dev *dmadev;
> >> +
> >> +	mchan = to_hidma_chan(chan);
> >> +	dmadev = to_hidma_dev(mchan->chan.device);
> >> +	if (!mchan->paused) {
> >> +		pm_runtime_get_sync(dmadev->ddev.dev);
> >> +		if (hidma_ll_pause(dmadev->lldev))
> >> +			dev_warn(dmadev->ddev.dev, "channel did not stop\n");
> >> +		mchan->paused = true;
> >> +		pm_runtime_mark_last_busy(dmadev->ddev.dev);
> >> +		pm_runtime_put_autosuspend(dmadev->ddev.dev);
> >> +	}
> >> +	return 0;
> >> +}
> > 
> > This is interesting, we associate pause/resume for slave dma ops and not for
> > memcpy ops, what is the reason for adding pause/resume here?
> 
> Why is it limited to the slave device only? I can queue a bunch of
> requests. I can pause and resume their execution with the current
> implementation.

Traditionally no one paused memcpy... People want the copy to be done with
as fast as possible :)

> 
> > 
> >> +static int hidma_remove(struct platform_device *pdev)
> >> +{
> >> +	struct hidma_dev *dmadev = platform_get_drvdata(pdev);
> >> +
> >> +	pm_runtime_get_sync(dmadev->ddev.dev);
> >> +	dma_async_device_unregister(&dmadev->ddev);
> >> +	hidma_debug_uninit(dmadev);
> >> +	hidma_ll_uninit(dmadev->lldev);
> >> +	hidma_free(dmadev);
> >> +
> >> +	dev_info(&pdev->dev, "HI-DMA engine removed\n");
> >> +	pm_runtime_put_sync_suspend(&pdev->dev);
> >> +	pm_runtime_disable(&pdev->dev);
> > 
> > and your irq is still active and can invoke your irq handler!
> > 
> 
> why? I shutdown the IRQ in hidma_ll_uninit and request the interrupt
> with devm_request_irq. As soon as this driver is removed, the interrupt
> should be released by the managed code.

but there is a delay between that and free getting called. Since you don't
free up explicitly you can still have irq and tasklets scheduled.

Recommendation is that free up irq or ensure none are scheduled and
disabled

-- 
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#1281221

On 12/1/2015 6:34 AM, Vinod Koul wrote:
> On Mon, Nov 30, 2015 at 03:06:36PM -0500, Sinan Kaya wrote:
>> I have split the debugfs support from this patch to its own patch. Any
>> other idea on how else you'd break the code? I can take one more step
>> and separate the lower layer from the OS layer by using stub functions
>> on the initial commit.
> 
> Yes the ll.c can be a separate patch and no need to add placeholders as
> makefile can be last
> 

ok. I'll create a new patch file with the Makefile and hidma_ll.c only.

>>>
>>>> +static enum dma_status hidma_tx_status(struct dma_chan *dmach,
>>>> +			dma_cookie_t cookie, struct dma_tx_state *txstate)
>>>> +{
>>>> +	struct hidma_chan *mchan = to_hidma_chan(dmach);
>>>> +	enum dma_status ret;
>>>> +
>>>> +	if (mchan->paused)
>>>> +		ret = DMA_PAUSED;
>>>
>>> This is not quite right. The status query is for a descriptor and NOT for
>>> channel. Here if the descriptor queried was running then it would be paused
>>> for the rest pending txn, it would be DMA_IN_PROGRESS.
>>
>> The channel can be paused by the hypervisor. If it is paused, then no
>> other transaction will go through including the pending requests. That's
>> why, I'm checking the state first.
> 
> You are missing the point. Channel can be paused, yes but the descriptor
> is in queue and is not paused. The descriptor running is paused, yes.
> There is subtle difference between these

I'll follow your recommendation. PAUSE for the currently active
descriptor and DMA_IN_PROGRESS for the rest.

> 
>>>> +static dma_cookie_t hidma_tx_submit(struct dma_async_tx_descriptor *txd)
>>>> +{
>>>> +	struct hidma_chan *mchan = to_hidma_chan(txd->chan);
>>>> +	struct hidma_dev *dmadev = mchan->dmadev;
>>>> +	struct hidma_desc *mdesc;
>>>> +	unsigned long irqflags;
>>>> +	dma_cookie_t cookie;
>>>> +
>>>> +	if (!hidma_ll_isenabled(dmadev->lldev))
>>>> +		return -ENODEV;
>>>
>>> is this not too late for this check, you should fail this on prepare
>>> method
>>
>> The channels can be paused by the hypervisor at runtime after the guest
>> OS boot. The client might have allocated the channels during guest
>> machine boot. If a channel is paused and client makes a request, client
>> will never get the callback. By placing this check, I'm looking at the
>> runtime status of the channel and rejecting the transmit request right
>> ahead.
> 
> In this case you have request already given to you, here the request is
> submitted to the pending queue, 

No, it is not. Putting into the pending queue is done after this check
not before.

I'm rejecting the queue request directly here as HIDMA channel is no
longer functional. I'd rather do active error handling rather than
passive error handling. Debugging of passive faults are much more difficult.

> if hypervisor has paused you, so the entire
> txn queue is paused. But from API semantics I would argue that this should be
> accepted and suffer the same fate as already submitted txns
> 



>>
>>>
>>>
>>>> +static int hidma_alloc_chan_resources(struct dma_chan *dmach)
>>>> +{
>>>> +	struct hidma_chan *mchan = to_hidma_chan(dmach);
>>>> +	struct hidma_dev *dmadev = mchan->dmadev;
>>>> +	struct hidma_desc *mdesc, *tmp;
>>>> +	unsigned long irqflags;
>>>> +	LIST_HEAD(descs);
>>>> +	unsigned int i;
>>>> +	int rc = 0;
>>>> +
>>>> +	if (mchan->allocated)
>>>> +		return 0;
>>>> +
>>>> +	/* Alloc descriptors for this channel */
>>>> +	for (i = 0; i < dmadev->nr_descriptors; i++) {
>>>> +		mdesc = kzalloc(sizeof(struct hidma_desc), GFP_KERNEL);
>>>
>>> GFP_NOWAIT pls, this can be called from atomic context
>>
>> I'll change it, but why would anyone allocate a channel in an interrupt
>> handler?
> 
> remember this is dmaengine, where people traditionally wanted to offload
> from cpu and were not allowed to sleep.
> 
> I think am okay with this one..
> 
>>
>>>
>>>> +		if (!mdesc) {
>>>> +			rc = -ENOMEM;
>>>> +			break;
>>>> +		}
>>>> +		dma_async_tx_descriptor_init(&mdesc->desc, dmach);
>>>> +		mdesc->desc.flags = DMA_CTRL_ACK;
>>>
>>> what is the purpose of setting this flag here
>>
>> It means that the code only supports interrupt. Maybe, you can correct
>> me here. I couldn't see a very useful info about the DMA engine flags.
>> My understanding is that DMA_CTRL_ACK means user wants an interrupt
>> based callback.
> 
> Right user wants, you are not user though
> 

Fair enough.

>>
>> If DMA_CTRL_ACK is not specified, then user wants to poll for the
>> results. The current code only supports the interrupt based delivery for
>> callbacks. Polling support is another to-do in my list for small sized
>> transfers.
> 
> See the documentation for flags and usage. The point here is that user
> should set this. I know some old driver do this but that is not right
> 

I'll remove it.

>>
>>>
>>>
>>>> +static int hidma_remove(struct platform_device *pdev)
>>>> +{
>>>> +	struct hidma_dev *dmadev = platform_get_drvdata(pdev);
>>>> +
>>>> +	pm_runtime_get_sync(dmadev->ddev.dev);
>>>> +	dma_async_device_unregister(&dmadev->ddev);
>>>> +	hidma_debug_uninit(dmadev);
>>>> +	hidma_ll_uninit(dmadev->lldev);
>>>> +	hidma_free(dmadev);
>>>> +
>>>> +	dev_info(&pdev->dev, "HI-DMA engine removed\n");
>>>> +	pm_runtime_put_sync_suspend(&pdev->dev);
>>>> +	pm_runtime_disable(&pdev->dev);
>>>
>>> and your irq is still active and can invoke your irq handler!
>>>
>>
>> why? I shutdown the IRQ in hidma_ll_uninit and request the interrupt
>> with devm_request_irq. As soon as this driver is removed, the interrupt
>> should be released by the managed code.
> 
> but there is a delay between that and free getting called. Since you don't
> free up explicitly you can still have irq and tasklets scheduled.
> 
> Recommendation is that free up irq or ensure none are scheduled and
> disabled
> 
I looked at other drivers. They seem to be disabling the IRQ right after
unregistering the DMA device from DMA engine. I'll follow the same by
adding an explicit dma_free_irq call into hidma_remove function.


-- 
Sinan Kaya
Qualcomm Technologies, Inc. on behalf of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a
Linux Foundation Collaborative Project
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#1282272

On 12/1/2015 4:16 PM, Sinan Kaya wrote:
>>>> >>>
>>>>> >>>> +static enum dma_status hidma_tx_status(struct dma_chan *dmach,
>>>>> >>>> +			dma_cookie_t cookie, struct dma_tx_state *txstate)
>>>>> >>>> +{
>>>>> >>>> +	struct hidma_chan *mchan = to_hidma_chan(dmach);
>>>>> >>>> +	enum dma_status ret;
>>>>> >>>> +
>>>>> >>>> +	if (mchan->paused)
>>>>> >>>> +		ret = DMA_PAUSED;
>>>> >>>
>>>> >>> This is not quite right. The status query is for a descriptor and NOT for
>>>> >>> channel. Here if the descriptor queried was running then it would be paused
>>>> >>> for the rest pending txn, it would be DMA_IN_PROGRESS.
>>> >>
>>> >> The channel can be paused by the hypervisor. If it is paused, then no
>>> >> other transaction will go through including the pending requests. That's
>>> >> why, I'm checking the state first.
>> > 
>> > You are missing the point. Channel can be paused, yes but the descriptor
>> > is in queue and is not paused. The descriptor running is paused, yes.
>> > There is subtle difference between these
> I'll follow your recommendation. PAUSE for the currently active
> descriptor and DMA_IN_PROGRESS for the rest.
> 

I'm now confused.

I looked at several DMA driver implementations.

1. They call dma_cookie_status function to see if the job is done.
2. If done, they return right ahead.
3. Otherwise, dma_cookie_status returns DMA_IN_PROGRESS.
4. Next the code checks if the channel is paused and return value is
DMA_IN_PROGRESS. The code changes return code to DMA_PAUSED.

Whereas, I was returning paused first before even checking if the
descriptor is done. Are you OK with the sequence 1..4 above?

-- 
Sinan Kaya
Qualcomm Technologies, Inc. on behalf of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a
Linux Foundation Collaborative Project
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#1284487

On Wed, Dec 02, 2015 at 02:04:05PM -0500, Sinan Kaya wrote:
> >> > You are missing the point. Channel can be paused, yes but the descriptor
> >> > is in queue and is not paused. The descriptor running is paused, yes.
> >> > There is subtle difference between these
> > I'll follow your recommendation. PAUSE for the currently active
> > descriptor and DMA_IN_PROGRESS for the rest.
> > 
> 
> I'm now confused.
> 
> I looked at several DMA driver implementations.
> 
> 1. They call dma_cookie_status function to see if the job is done.
> 2. If done, they return right ahead.
> 3. Otherwise, dma_cookie_status returns DMA_IN_PROGRESS.
> 4. Next the code checks if the channel is paused and return value is
> DMA_IN_PROGRESS. The code changes return code to DMA_PAUSED.
> 
> Whereas, I was returning paused first before even checking if the
> descriptor is done. Are you OK with the sequence 1..4 above?

Yes am okay with this with slight change in 4.

You should set to PAUSED only for current descriptor and not for the ones in
queue

-- 
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#1286531

On 12/5/2015 3:00 AM, Vinod Koul wrote:
> On Wed, Dec 02, 2015 at 02:04:05PM -0500, Sinan Kaya wrote:
>>>>> You are missing the point. Channel can be paused, yes but the descriptor
>>>>> is in queue and is not paused. The descriptor running is paused, yes.
>>>>> There is subtle difference between these
>>> I'll follow your recommendation. PAUSE for the currently active
>>> descriptor and DMA_IN_PROGRESS for the rest.
>>>
>>
>> I'm now confused.
>>
>> I looked at several DMA driver implementations.
>>
>> 1. They call dma_cookie_status function to see if the job is done.
>> 2. If done, they return right ahead.
>> 3. Otherwise, dma_cookie_status returns DMA_IN_PROGRESS.
>> 4. Next the code checks if the channel is paused and return value is
>> DMA_IN_PROGRESS. The code changes return code to DMA_PAUSED.
>>
>> Whereas, I was returning paused first before even checking if the
>> descriptor is done. Are you OK with the sequence 1..4 above?
> 
> Yes am okay with this with slight change in 4.
> 
> You should set to PAUSED only for current descriptor and not for the ones in
> queue
> 
OK, I'll work on it.

-- 
Sinan Kaya
Qualcomm Technologies, Inc. on behalf of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a
Linux Foundation Collaborative Project
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#1288895

On 12/5/2015 3:00 AM, Vinod Koul wrote:
> On Wed, Dec 02, 2015 at 02:04:05PM -0500, Sinan Kaya wrote:
>>>>> You are missing the point. Channel can be paused, yes but the descriptor
>>>>> is in queue and is not paused. The descriptor running is paused, yes.
>>>>> There is subtle difference between these
>>> I'll follow your recommendation. PAUSE for the currently active
>>> descriptor and DMA_IN_PROGRESS for the rest.
>>>
>>
>> I'm now confused.
>>
>> I looked at several DMA driver implementations.
>>
>> 1. They call dma_cookie_status function to see if the job is done.
>> 2. If done, they return right ahead.
>> 3. Otherwise, dma_cookie_status returns DMA_IN_PROGRESS.
>> 4. Next the code checks if the channel is paused and return value is
>> DMA_IN_PROGRESS. The code changes return code to DMA_PAUSED.
>>
>> Whereas, I was returning paused first before even checking if the
>> descriptor is done. Are you OK with the sequence 1..4 above?
> 
> Yes am okay with this with slight change in 4.
> 
> You should set to PAUSED only for current descriptor and not for the ones in
> queue
> 

OK. I'll post a new version with this. Is there any other comment that
needed to be addressed?

-- 
Sinan Kaya
Qualcomm Technologies, Inc. on behalf of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a
Linux Foundation Collaborative Project
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#1289363

On Thu, Dec 10, 2015 at 03:10:48PM -0500, Sinan Kaya wrote:
> On 12/5/2015 3:00 AM, Vinod Koul wrote:
> > On Wed, Dec 02, 2015 at 02:04:05PM -0500, Sinan Kaya wrote:
> >>>>> You are missing the point. Channel can be paused, yes but the descriptor
> >>>>> is in queue and is not paused. The descriptor running is paused, yes.
> >>>>> There is subtle difference between these
> >>> I'll follow your recommendation. PAUSE for the currently active
> >>> descriptor and DMA_IN_PROGRESS for the rest.
> >>>
> >>
> >> I'm now confused.
> >>
> >> I looked at several DMA driver implementations.
> >>
> >> 1. They call dma_cookie_status function to see if the job is done.
> >> 2. If done, they return right ahead.
> >> 3. Otherwise, dma_cookie_status returns DMA_IN_PROGRESS.
> >> 4. Next the code checks if the channel is paused and return value is
> >> DMA_IN_PROGRESS. The code changes return code to DMA_PAUSED.
> >>
> >> Whereas, I was returning paused first before even checking if the
> >> descriptor is done. Are you OK with the sequence 1..4 above?
> > 
> > Yes am okay with this with slight change in 4.
> > 
> > You should set to PAUSED only for current descriptor and not for the ones in
> > queue
> > 
> 
> OK. I'll post a new version with this. Is there any other comment that
> needed to be addressed?

Looks okay to me

-- 
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