[Intel-gfx] [PATCH 0/7] drm/i915: Use the memcpy_from_wc function from drm

Das, Nirmoy nirmoy.das at linux.intel.com
Wed Feb 23 13:21:30 UTC 2022

On 23/02/2022 12:08, Balasubramani Vivekanandan wrote:
> On 23.02.2022 10:02, Das, Nirmoy wrote:
>> On 22/02/2022 15:51, Balasubramani Vivekanandan wrote:
>>> drm_memcpy_from_wc() performs fast copy from WC memory type using
>>> non-temporal instructions. Now there are two similar implementations of
>>> this function. One exists in drm_cache.c as drm_memcpy_from_wc() and
>>> another implementation in i915/i915_memcpy.c as i915_memcpy_from_wc().
>>> drm_memcpy_from_wc() was the recent addition through the series
>>> https://patchwork.freedesktop.org/patch/436276/?series=90681&rev=6
>>> The goal of this patch series is to change all users of
>>> i915_memcpy_from_wc() to drm_memcpy_from_wc() and a have common
>>> implementation in drm and eventually remove the copy from i915.
>>> Another benefit of using memcpy functions from drm is that
>>> drm_memcpy_from_wc() is available for non-x86 architectures.
>>> i915_memcpy_from_wc() is implemented only for x86 and prevents building
>>> i915 for ARM64.
>>> drm_memcpy_from_wc() does fast copy using non-temporal instructions for
>>> x86 and for other architectures makes use of memcpy() family of
>>> functions as fallback.
>>> Another major difference is unlike i915_memcpy_from_wc(),
>>> drm_memcpy_from_wc() will not fail if the passed address argument is not
>>> alignment to be used with non-temporal load instructions or if the
>>> platform lacks support for those instructions (non-temporal load
>>> instructions are provided through SSE4.1 instruction set extension).
>>> Instead drm_memcpy_from_wc() continues with fallback functions to
>>> complete the copy.
>>> This relieves the caller from checking the return value of
>>> i915_memcpy_from_wc() and explicitly using a fallback.
>>> Follow up series will be created to remove the memcpy_from_wc functions
>>> from i915 once the dependency is completely removed.
>> Overall the series looks good to me but I think you can add another patch to
>> remove
>> i915_memcpy_from_wc() as I don't see any other usages left after this series, may be I
>> am missing something?
> I have changed all users of i915_memcpy_from_wc() to drm function. But
> this is another function i915_unaligned_memcpy_from_wc() in
> i915_memcpy.c which is blocking completely eliminating the i915_memcpy.c
> file from i915.
> This function accepts unaligned source address and does fast copy only
> for the aligned region of memory and remaining part is copied using
> memcpy function.
> Either I can move i915_unaligned_memcpy_from_wc() also to drm but I am
> concerned since it is more a platform specific handling, does it make
> sense to keep it in drm.
> Else I have retain to i915_unaligned_memcpy_from_wc() inside i915 and
> refactor the function to use drm_memcpy_from_wc() instead of the
> __memcpy_ntdqu().

I think for completeness it makes sense to remove i915_memcpy_from_wc() 
and its helper functions

in this series.  I don't think we can have 
i915_unaligned_memcpy_from_wc() if want i915 on ARM[0] so I think

you can remove usages of i915_unaligned_memcpy_from_wc() as well.

[0]IIUC  CI_BUG_ON() check in i915_unaligned_memcpy_from_wc() will 
raise  a build error on ARM



> But before I could do more changes, I wanted feedback on the current
> change. So I decided to go ahead with creating series for review.
> Regards,
> Bala
>> Regards,
>> Nirmoy
>>> Cc: Jani Nikula <jani.nikula at intel.com>
>>> Cc: Lucas De Marchi <lucas.demarchi at intel.com>
>>> Cc: David Airlie <airlied at linux.ie>
>>> Cc: Daniel Vetter <daniel at ffwll.ch>
>>> Cc: Chris Wilson <chris.p.wilson at intel.com>
>>> Cc: Thomas Hellstr_m <thomas.hellstrom at linux.intel.com>
>>> Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
>>> Cc: Rodrigo Vivi <rodrigo.vivi at intel.com>
>>> Cc: Tvrtko Ursulin <tvrtko.ursulin at linux.intel.com>
>>> Balasubramani Vivekanandan (7):
>>>     drm: Relax alignment constraint for destination address
>>>     drm: Add drm_memcpy_from_wc() variant which accepts destination
>>>       address
>>>     drm/i915: use the memcpy_from_wc call from the drm
>>>     drm/i915/guc: use the memcpy_from_wc call from the drm
>>>     drm/i915/selftests: use the memcpy_from_wc call from the drm
>>>     drm/i915/gt: Avoid direct dereferencing of io memory
>>>     drm/i915: Avoid dereferencing io mapped memory
>>>    drivers/gpu/drm/drm_cache.c                   | 98 +++++++++++++++++--
>>>    drivers/gpu/drm/i915/gem/i915_gem_object.c    |  8 +-
>>>    drivers/gpu/drm/i915/gt/selftest_reset.c      | 21 ++--
>>>    drivers/gpu/drm/i915/gt/uc/intel_guc_log.c    | 11 ++-
>>>    drivers/gpu/drm/i915/i915_gpu_error.c         | 45 +++++----
>>>    .../drm/i915/selftests/intel_memory_region.c  |  8 +-
>>>    include/drm/drm_cache.h                       |  3 +
>>>    7 files changed, 148 insertions(+), 46 deletions(-)

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