linux-kernel - Re: [PATCH] drm/panfrost: fix GENERIC

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Message-ID: <55689951-d9df-3f5e-4edc-23c86259ef2f@arm.com>
Date:   Wed, 18 Jan 2023 11:19:02 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Steven Price <steven.price@....com>,
        Arnd Bergmann <arnd@...nel.org>, Rob Herring <robh@...nel.org>,
        Tomeu Vizoso <tomeu.vizoso@...labora.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Alyssa Rosenzweig <alyssa.rosenzweig@...labora.com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Adrián Larumbe <adrian.larumbe@...labora.com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/panfrost: fix GENERIC_ATOMIC64 dependency

On 2023-01-18 11:09, Steven Price wrote:
> On 17/01/2023 16:44, Arnd Bergmann wrote:
>> From: Arnd Bergmann <arnd@...db.de>
>>
>> On ARMv5 and earlier, a randconfig build can still run into
>>
>> WARNING: unmet direct dependencies detected for IOMMU_IO_PGTABLE_LPAE
>>    Depends on [n]: IOMMU_SUPPORT [=y] && (ARM [=y] || ARM64 || COMPILE_TEST [=y]) && !GENERIC_ATOMIC64 [=y]
>>    Selected by [y]:
>>    - DRM_PANFROST [=y] && HAS_IOMEM [=y] && DRM [=y] && (ARM [=y] || ARM64 || COMPILE_TEST [=y] && !GENERIC_ATOMIC64 [=y]) && MMU [=y]
>>
>> Rework the dependencies to always require a working cmpxchg64.
>>
>> Fixes: db594ba3fcf9 ("drm/panfrost: depend on !GENERIC_ATOMIC64 when using COMPILE_TEST")
> 
> Looking at db594ba3fcf9 - it states:
> 
>>      Since panfrost has a 'select' on IOMMU_IO_PGTABLE_LPAE we must depend on
>>      the same set of flags. Otherwise IOMMU_IO_PGTABLE_LPAE will be forced on
>>      even though it cannot build (no support for cmpxchg64).
> 
> And at the time the dependencies on IOMMU_IO_PGTABLE_LPAE were exactly
> these.
> 
> However d286a58bc8f4 ("iommu: Tidy up io-pgtable dependencies")
> (currently in the iommu tree) changed the depends to split the
> !GENERIC_ATOMIC64 out. So we could argue that really that's the commit
> that should be blamed in the fixes line.

Oh bum... indeed this is entirely my fault for forgetting about our one 
"foreign" io-pgtable user in that commit, sorry about that.

> However there's no harm in this being backported further than it
> strictly needs to be, and it's clearly better having the
> !GENERIC_ATOMIC64 split out. So I'll merge this to drm-misc-fixes.

Thanks both!

Robin.

> 
> Reviewed-by: Steven Price <steven.price@....com>
> 
> Thanks!
> 
> Steve
> 
>> Signed-off-by: Arnd Bergmann <arnd@...db.de>
>> ---
>>   drivers/gpu/drm/panfrost/Kconfig | 3 ++-
>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/panfrost/Kconfig b/drivers/gpu/drm/panfrost/Kconfig
>> index 079600328be1..e6403a9d66ad 100644
>> --- a/drivers/gpu/drm/panfrost/Kconfig
>> +++ b/drivers/gpu/drm/panfrost/Kconfig
>> @@ -3,7 +3,8 @@
>>   config DRM_PANFROST
>>   	tristate "Panfrost (DRM support for ARM Mali Midgard/Bifrost GPUs)"
>>   	depends on DRM
>> -	depends on ARM || ARM64 || (COMPILE_TEST && !GENERIC_ATOMIC64)
>> +	depends on ARM || ARM64 || COMPILE_TEST
>> +	depends on !GENERIC_ATOMIC64    # for IOMMU_IO_PGTABLE_LPAE
>>   	depends on MMU
>>   	select DRM_SCHED
>>   	select IOMMU_SUPPORT
>