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Commit 23c18c71 authored by Daniel Vetter's avatar Daniel Vetter
Browse files

drm/i915: fixup in-line clflushing on bit17 swizzled bos 



The issue is that with inline clflushing the clflushing isn't properly
swizzled. Fix this by
- always clflushing entire 128 byte chunks and
- unconditionally flush before writes when swizzling a given page.
  We could be clever and check whether we pwrite a partial 128 byte
  chunk instead of a partial cacheline, but I've figured that's not
  worth it.

Now the usual approach is to fold this into the original patch series, but
I've opted against this because
- this fixes a corner case only very old userspace relies on and
- I'd like to not invalidate all the testing the pwrite rewrite has gotten.

This fixes the regression notice by tests/gem_tiled_partial_prite_pread
from i-g-t. Unfortunately it doesn't fix the issues with partial pwrites to
tiled buffers on bit17 swizzling machines. But that is also broken without
the pwrite patches, so likely a different issue (or a problem with the
testcase).

v2: Simplify the patch by dropping the overly clever partial write
logic for swizzled pages.

Reviewed-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
Signed-Off-by: default avatarDaniel Vetter <daniel.vetter@ffwll.ch>
parent f56f821f

drivers/gpu/drm/i915/i915_gem.c

+32 −7
Original line number Diff line number Diff line
@@ -313,6 +313,28 @@ shmem_pread_fast(struct page *page, int shmem_page_offset, int page_length, 
	return ret;

}



static void

shmem_clflush_swizzled_range(char *addr, unsigned long length,

			     bool swizzled)

{

	if (swizzled) {

		unsigned long start = (unsigned long) addr;

		unsigned long end = (unsigned long) addr + length;



		/* For swizzling simply ensure that we always flush both

		 * channels. Lame, but simple and it works. Swizzled

		 * pwrite/pread is far from a hotpath - current userspace

		 * doesn't use it at all. */

		start = round_down(start, 128);

		end = round_up(end, 128);



		drm_clflush_virt_range((void *)start, end - start);

	} else {

		drm_clflush_virt_range(addr, length);

	}



}



/* Only difference to the fast-path function is that this can handle bit17

 * and uses non-atomic copy and kmap functions. */

static int
@@ -325,8 +347,9 @@ shmem_pread_slow(struct page *page, int shmem_page_offset, int page_length, 


	vaddr = kmap(page);

	if (needs_clflush)

		drm_clflush_virt_range(vaddr + shmem_page_offset,

				       page_length);

		shmem_clflush_swizzled_range(vaddr + shmem_page_offset,

					     page_length,

					     page_do_bit17_swizzling);



	if (page_do_bit17_swizzling)

		ret = __copy_to_user_swizzled(user_data,
@@ -637,9 +660,10 @@ shmem_pwrite_slow(struct page *page, int shmem_page_offset, int page_length, 
	int ret;



	vaddr = kmap(page);

	if (needs_clflush_before)

		drm_clflush_virt_range(vaddr + shmem_page_offset,

				       page_length);

	if (needs_clflush_before || page_do_bit17_swizzling)

		shmem_clflush_swizzled_range(vaddr + shmem_page_offset,

					     page_length,

					     page_do_bit17_swizzling);

	if (page_do_bit17_swizzling)

		ret = __copy_from_user_swizzled(vaddr, shmem_page_offset,

						user_data,
@@ -649,8 +673,9 @@ shmem_pwrite_slow(struct page *page, int shmem_page_offset, int page_length, 
				       user_data,

				       page_length);

	if (needs_clflush_after)

		drm_clflush_virt_range(vaddr + shmem_page_offset,

				       page_length);

		shmem_clflush_swizzled_range(vaddr + shmem_page_offset,

					     page_length,

					     page_do_bit17_swizzling);

	kunmap(page);



	return ret;