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Re: [PATCH 2/2] iommu/tegra-gart: Add support for struct iommu_device

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  Re: [PATCH 2/2] iommu/tegra-gart: Add support for struct iommu_device Dmitry Osipenko <digetx@gmail.com> - 2017-08-17 00:30 +0200
    Re: [PATCH 2/2] iommu/tegra-gart: Add support for struct iommu_device Thierry Reding <thierry.reding@gmail.com> - 2017-08-17 16:00 +0200
      Re: [PATCH 2/2] iommu/tegra-gart: Add support for struct iommu_device Dmitry Osipenko <digetx@gmail.com> - 2017-08-17 19:20 +0200

#1713376 — Re: [PATCH 2/2] iommu/tegra-gart: Add support for struct iommu_device

Hello Joerg,

On 10.08.2017 01:29, Joerg Roedel wrote:
> From: Joerg Roedel <jroedel@suse.de>
> 
> Add a struct iommu_device to each tegra-gart and register it
> with the iommu-core. Also link devices added to the driver
> to their respective hardware iommus.
> 
> Signed-off-by: Joerg Roedel <jroedel@suse.de>
> ---
>  drivers/iommu/tegra-gart.c | 26 ++++++++++++++++++++++++++
>  1 file changed, 26 insertions(+)
> 

Reviewed-by: Dmitry Osipenko <digetx@gmail.com>
Tested-by: Dmitry Osipenko <digetx@gmail.com>

> diff --git a/drivers/iommu/tegra-gart.c b/drivers/iommu/tegra-gart.c
> index 29bafc6..b62f790 100644
> --- a/drivers/iommu/tegra-gart.c
> +++ b/drivers/iommu/tegra-gart.c

[snip]

> @@ -449,6 +472,9 @@ static int tegra_gart_remove(struct platform_device *pdev)
>  {

BTW, GART's driver can't be build as a module, so this function is pretty much a
dead code. Probably worth considering its removal.

>  	struct gart_device *gart = platform_get_drvdata(pdev);
>  
> +	iommu_device_unregister(&gart->iommu);
> +	iommu_device_sysfs_remove(&gart->iommu);
> +
>  	writel(0, gart->regs + GART_CONFIG);
>  	if (gart->savedata)
>  		vfree(gart->savedata);
> 


-- 
Dmitry

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#1714059

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On Thu, Aug 17, 2017 at 01:21:52AM +0300, Dmitry Osipenko wrote:
> Hello Joerg,
> 
> On 10.08.2017 01:29, Joerg Roedel wrote:
> > From: Joerg Roedel <jroedel@suse.de>
> > 
> > Add a struct iommu_device to each tegra-gart and register it
> > with the iommu-core. Also link devices added to the driver
> > to their respective hardware iommus.
> > 
> > Signed-off-by: Joerg Roedel <jroedel@suse.de>
> > ---
> >  drivers/iommu/tegra-gart.c | 26 ++++++++++++++++++++++++++
> >  1 file changed, 26 insertions(+)
> > 
> 
> Reviewed-by: Dmitry Osipenko <digetx@gmail.com>
> Tested-by: Dmitry Osipenko <digetx@gmail.com>
> 
> > diff --git a/drivers/iommu/tegra-gart.c b/drivers/iommu/tegra-gart.c
> > index 29bafc6..b62f790 100644
> > --- a/drivers/iommu/tegra-gart.c
> > +++ b/drivers/iommu/tegra-gart.c
> 
> [snip]
> 
> > @@ -449,6 +472,9 @@ static int tegra_gart_remove(struct platform_device *pdev)
> >  {
> 
> BTW, GART's driver can't be build as a module, so this function is pretty much a
> dead code. Probably worth considering its removal.

Technically you can unbind the driver via sysfs, in which case this
function would still be called. That said, all sorts of things will
probably start to crash when you do that. I'd like to think that we
will eventually be able to deal with this sanely (there's some work
in progress to establish stronger links between devices, so that we
can sanely deal with this kind of dependency), so I think it's okay
to keep this around in case we ever get there.

I don't have any objections to making the driver unloadable if that
is what everyone else prefers, though. In that case, however, there
are more steps involved than just removing the ->remove() callback.

Thierry

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#1714234

On 17.08.2017 16:52, Thierry Reding wrote:
> On Thu, Aug 17, 2017 at 01:21:52AM +0300, Dmitry Osipenko wrote:
>> Hello Joerg,
>>
>> On 10.08.2017 01:29, Joerg Roedel wrote:
>>> From: Joerg Roedel <jroedel@suse.de>
>>>
>>> Add a struct iommu_device to each tegra-gart and register it
>>> with the iommu-core. Also link devices added to the driver
>>> to their respective hardware iommus.
>>>
>>> Signed-off-by: Joerg Roedel <jroedel@suse.de>
>>> ---
>>>  drivers/iommu/tegra-gart.c | 26 ++++++++++++++++++++++++++
>>>  1 file changed, 26 insertions(+)
>>>
>>
>> Reviewed-by: Dmitry Osipenko <digetx@gmail.com>
>> Tested-by: Dmitry Osipenko <digetx@gmail.com>
>>
>>> diff --git a/drivers/iommu/tegra-gart.c b/drivers/iommu/tegra-gart.c
>>> index 29bafc6..b62f790 100644
>>> --- a/drivers/iommu/tegra-gart.c
>>> +++ b/drivers/iommu/tegra-gart.c
>>
>> [snip]
>>
>>> @@ -449,6 +472,9 @@ static int tegra_gart_remove(struct platform_device *pdev)
>>>  {
>>
>> BTW, GART's driver can't be build as a module, so this function is pretty much a
>> dead code. Probably worth considering its removal.
> 
> Technically you can unbind the driver via sysfs, in which case this
> function would still be called. That said, all sorts of things will
> probably start to crash when you do that. I'd like to think that we
> will eventually be able to deal with this sanely (there's some work
> in progress to establish stronger links between devices, so that we
> can sanely deal with this kind of dependency), so I think it's okay
> to keep this around in case we ever get there.
> 

Good point! I tried to unbind and with this patch kernel crashes immediately:

[  193.968506] kernel BUG at mm/slab.c:2816!
[  193.968912] Internal error: Oops - BUG: 0 [#1] PREEMPT SMP ARM
[  193.969466] Modules linked in:
[  193.969822] CPU: 1 PID: 1177 Comm: bash Not tainted
4.13.0-rc5-next-20170816-00067-gd320d19b76f8 #593
[  193.970653] Hardware name: NVIDIA Tegra SoC (Flattened Device Tree)
[  193.971313] task: ee31e380 task.stack: ee394000
[  193.971771] PC is at ___cache_free+0x374/0x47c
[  193.972261] LR is at 0x1
[  193.972539] pc : [<c02776ec>]    lr : [<00000001>]    psr: 200b0093
[  193.973112] sp : ee395dd0  ip : 00000009  fp : 00000000
[  193.973603] r10: 00000480  r9 : 2e844000  r8 : c1814d8c
[  193.974097] r7 : 005e4c40  r6 : c0f91fc0  r5 : ef262480  r4 : ef0003c0
[  193.974694] r3 : ef262400  r2 : ef262000  r1 : 00000400  r0 : 00000004

[snip]

[  193.991288] [<c02776ec>] (___cache_free) from [<c0278230>] (kfree+0xbc/0x260)
[  193.991978] [<c0278230>] (kfree) from [<c058897c>] (device_release+0x2c/0x90)
[  193.992732] [<c058897c>] (device_release) from [<c0ab6f14>]
(kobject_put+0x8c/0xe8)
[  193.993474] [<c0ab6f14>] (kobject_put) from [<c0527868>]
(tegra_gart_remove+0x1c/0x58)
[  193.994320] [<c0527868>] (tegra_gart_remove) from [<c058f770>]
(platform_drv_remove+0x24/0x3c)
[  193.995121] [<c058f770>] (platform_drv_remove) from [<c058db30>]
(device_release_driver_internal+0x15c/0x204)
[  193.996033] [<c058db30>] (device_release_driver_internal) from [<c058c2fc>]
(unbind_store+0x7c/0xfc)
[  193.996890] [<c058c2fc>] (unbind_store) from [<c02f8078>]
(kernfs_fop_write+0x104/0x208)
[  193.997661] [<c02f8078>] (kernfs_fop_write) from [<c027f6ec>]
(__vfs_write+0x1c/0x128)
[  193.998445] [<c027f6ec>] (__vfs_write) from [<c02810b8>] (vfs_write+0xa4/0x168)
[  194.017668] [<c02810b8>] (vfs_write) from [<c0281f0c>] (SyS_write+0x3c/0x90)
[  194.038493] [<c0281f0c>] (SyS_write) from [<c0107ce0>]
(ret_fast_syscall+0x0/0x1c)
[  194.057182] Code: e3a03000 ebfff54e eaffffe2 e7f001f2 (e7f001f2)

Without this patch, it crashes too after unbinding but not immediately. Either
way unbinding isn't useful for this device.

> I don't have any objections to making the driver unloadable if that
> is what everyone else prefers, though. In that case, however, there
> are more steps involved than just removing the ->remove() callback.
> 
Indeed!

-- 
Dmitry

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