On 6/1/21 2:27 PM, Jani Nikula wrote:

On Tue, 01 Jun 2021, Thomas Hellström thomas.hellstrom@linux.intel.com wrote:

...

Reading out of write-combining mapped memory is typically very slow since the CPU doesn't prefetch. However some archs have special instructions to do this.

So add a best-effort memcpy_from_wc taking dma-buf-map pointer arguments that attempts to use a fast prefetching memcpy and otherwise falls back to ordinary memcopies, taking the iomem tagging into account.

The code is largely copied from i915_memcpy_from_wc.

Cc: Daniel Vetter daniel@ffwll.ch Cc: Christian König christian.koenig@amd.com Suggested-by: Daniel Vetter daniel@ffwll.ch Signed-off-by: Thomas Hellström thomas.hellstrom@linux.intel.com Acked-by: Christian König christian.koenig@amd.com Acked-by: Daniel Vetter daniel@ffwll.ch

---

v7:

• Perform a memcpy even if warning with in_interrupt(). Suggested by Christian König.
• Fix compilation failure on !X86 (Reported by kernel test robot lkp@intel.com)

v8:

• Skip kerneldoc for drm_memcpy_init_early()
• Export drm_memcpy_from_wc() also for non-x86.

---

Documentation/gpu/drm-mm.rst | 2 +- drivers/gpu/drm/drm_cache.c | 148 +++++++++++++++++++++++++++++++++++ drivers/gpu/drm/drm_drv.c | 2 + include/drm/drm_cache.h | 7 ++ 4 files changed, 158 insertions(+), 1 deletion(-)

diff --git a/Documentation/gpu/drm-mm.rst b/Documentation/gpu/drm-mm.rst index 21be6deadc12..c66058c5bce7 100644 --- a/Documentation/gpu/drm-mm.rst +++ b/Documentation/gpu/drm-mm.rst @@ -469,7 +469,7 @@ DRM MM Range Allocator Function References .. kernel-doc:: drivers/gpu/drm/drm_mm.c :export:

-DRM Cache Handling

+DRM Cache Handling and Fast WC memcpy()

The title underline needs to be as long as the title.

BR, Jani.

Thanks, Jani.

I think Daniel was trying to point this out to me as well with limited success. It's fixed now.

/Thomas