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

Balasubramani Vivekanandan balasubramani.vivekanandan at intel.com
Tue Feb 22 14:51:59 UTC 2022

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

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.

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
  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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