Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1190002 > unrolled thread

Re: question about drivers/dma/dma-jz4780.c

Back to article view | Back to linux.kernel

This discussion starts older than the indexed window; earlier articles aren't shown. The article labeled Started by below is the oldest one visible, not the original post.

Contents

  Re: question about drivers/dma/dma-jz4780.c Alex Smith <alex.smith@imgtec.com> - 2015-07-22 16:30 +0200
    Re: question about drivers/dma/dma-jz4780.c Vinod Koul <vinod.koul@intel.com> - 2015-07-23 19:20 +0200
      Re: question about drivers/dma/dma-jz4780.c Julia Lawall <julia.lawall@lip6.fr> - 2015-07-23 19:30 +0200
        Re: question about drivers/dma/dma-jz4780.c Alex Smith <alex.smith@imgtec.com> - 2015-07-24 10:30 +0200

#1190002 — Re: question about drivers/dma/dma-jz4780.c

On 21/07/2015 05:15, Vinod Koul wrote:
> On Mon, Jul 20, 2015 at 10:28:14AM +0200, Julia Lawall wrote:
>> On Mon, 20 Jul 2015, Alex Smith wrote:
>>
>>> On 19/07/2015 10:08, Julia Lawall wrote:
>>>> The file drivers/dma/dma-jz4780.c has a probe function that sets up irqs
>>>> using devm_request_irq.  The probe function then ends with:
>>>>
>>>> err_unregister_dev:
>>>> 	dma_async_device_unregister(dd);
>>>>
>>>> err_disable_clk:
>>>>           clk_disable_unprepare(jzdma->clk);
>>>> 	return ret;
>>>> }
>>>>
>>>> The remove function, on the other hand contains:
>>>>
>>>>           of_dma_controller_free(pdev->dev.of_node);
>>>>           devm_free_irq(&pdev->dev, jzdma->irq, jzdma);
>>>>           dma_async_device_unregister(&jzdma->dma_device);
>>>>
>>>> The need for calling devm_free_irq explicitly would be that it needs to
>>>> occur before dma_async_device_unregister, to eg avoid a reference to a
>>>> dangling pointer.  But devm_free_irq is implicitly called after the call
>>>> to dma_async_device_unregister at the end of the probe function.  Which
>>>> one is correct?
> Not just users but from a device management you are ensuring that your
> device is not able to send any more interrupts and also your tasklet is not
> spawned further. For this it is neccessary that devm_irq_free be called
> explcitly by devices
>>>>
>>>> julia
>>>
>>> Hi,
>>>
>>> I think the explicit devm_free_irq() here is unnecessary, as when remove is
>>> called there should be no remaining users of the DMA controller and therefore
>>> no chance of an IRQ occurring between the controller being unregistered and an
>>> implicit IRQ release afterwards.
> Are you ensuring that device can no longer sent interrupts and all instances
> of tasklet running or either completed are terminated and no further tasklet
> can be spawned?

Hi Vinod,

If I understand correctly, when remove() is called, there should be no 
more users of the DMA controller, enforced by the module reference count.

Wouldn't that guarantee that there are no more transactions running and 
therefore no chance of an interrupt from the controller or a tasklet 
still running?

Thanks,
Alex
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[toc] | [next] | [standalone]

#1191148

On Wed, Jul 22, 2015 at 03:26:01PM +0100, Alex Smith wrote:

> >>>I think the explicit devm_free_irq() here is unnecessary, as when remove is
> >>>called there should be no remaining users of the DMA controller and therefore
> >>>no chance of an IRQ occurring between the controller being unregistered and an
> >>>implicit IRQ release afterwards.
> >Are you ensuring that device can no longer sent interrupts and all instances
> >of tasklet running or either completed are terminated and no further tasklet
> >can be spawned?
> 
> Hi Vinod,
> 
> If I understand correctly, when remove() is called, there should be
> no more users of the DMA controller, enforced by the module
> reference count.
> 
> Wouldn't that guarantee that there are no more transactions running
> and therefore no chance of an interrupt from the controller or a
> tasklet still running?

That will only guarantee no new requests are recieved, but you may have
tasklet already scheduled or irq sent from HW how do you prevent that?

-- 
~Vinod

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[toc] | [prev] | [next] | [standalone]

#1191158

On Thu, 23 Jul 2015, Vinod Koul wrote:

> On Wed, Jul 22, 2015 at 03:26:01PM +0100, Alex Smith wrote:
>
> > >>>I think the explicit devm_free_irq() here is unnecessary, as when remove is
> > >>>called there should be no remaining users of the DMA controller and therefore
> > >>>no chance of an IRQ occurring between the controller being unregistered and an
> > >>>implicit IRQ release afterwards.
> > >Are you ensuring that device can no longer sent interrupts and all instances
> > >of tasklet running or either completed are terminated and no further tasklet
> > >can be spawned?
> >
> > Hi Vinod,
> >
> > If I understand correctly, when remove() is called, there should be
> > no more users of the DMA controller, enforced by the module
> > reference count.
> >
> > Wouldn't that guarantee that there are no more transactions running
> > and therefore no chance of an interrupt from the controller or a
> > tasklet still running?
>
> That will only guarantee no new requests are recieved, but you may have
> tasklet already scheduled or irq sent from HW how do you prevent that?

More genrally, I have seen another driver with synchronize_irq in the
remove function (dma/img-mdc-dma.c).  Would that be safe enough?  On the
other hand, if one is going to go to the trouble of putting that, maybe
one would do just as well to drop the devm for irqs and use free_irq in
place of synchronize_irq instead?

thanks,
julia
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[toc] | [prev] | [next] | [standalone]

#1191591

On 24/07/2015 07:30, Vinod Koul wrote:
> On Fri, Jul 24, 2015 at 07:51:28AM +0200, Julia Lawall wrote:
>>> Yes for dmaengine drivers I do ask this question which typically ends up in
>>> driver invoking devm_irq_free() in driver's remove callback
>>>
>>> IMHO don't think devm irq calls are very useful, they do make stuff
>>> complicate
>>
>> Would it be better then to just go back to request_irq (or whatever is
>> appropriate in this case).  It would seem that the devm property can never
>> be relied on, so there is no point to use it.
>
> Yes I do think that is right way in this case
>

Hmm, OK, I will drop the patch I submitted removing the explicit 
devm_free_irq() call and send a new one which stops using the devm IRQ 
functions, and kills the tasklets.

Thanks,
Alex
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[toc] | [prev] | [standalone]

Back to top | Article view | linux.kernel

csiph-web