Re: [PATCH 16/20] drm/i915/create: apply ALLOC_TOPDOWN by default

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On 03/02/2022 09:17, Thomas Hellström wrote:

On 1/26/22 16:21, Matthew Auld wrote:
Starting from DG2+, when dealing with LMEM, we assume that by default
all userspace allocations should be placed in the non-mappable portion
of LMEM.  Note that dumb buffers are not included here, since these are
not "GPU accelerated" and likely need CPU access.

In a later patch userspace will be able to provide a hint if CPU access
to the buffer is needed.

Signed-off-by: Matthew Auld <matthew.auld@xxxxxxxxx>
Cc: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>
---
  drivers/gpu/drm/i915/gem/i915_gem_create.c | 9 +++++++++
  1 file changed, 9 insertions(+)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_create.c b/drivers/gpu/drm/i915/gem/i915_gem_create.c
index 9402d4bf4ffc..e7456443f163 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_create.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_create.c
@@ -424,6 +424,15 @@ i915_gem_create_ext_ioctl(struct drm_device *dev, void *data,
          ext_data.n_placements = 1;
      }
+    /*
+     * TODO: add a userspace hint to force CPU_ACCESS for the object, which
+     * can override this.
+     */
+    if (!IS_DG1(i915) && (ext_data.n_placements > 1 ||
+                  ext_data.placements[0]->type !=
+                  INTEL_MEMORY_SYSTEM))
+        ext_data.flags |= I915_BO_ALLOC_TOPDOWN;

Perhaps we should include DG1 here as well, so that the same paths are taken regardless whether this is only a test on DG1?

I think the only reason was EXEC_CAPTURE, where atm we just reject anything marked with I915_BO_ALLOC_TOPDOWN, but that must not break existing DG1 uapi.





+
      obj = __i915_gem_object_create_user_ext(i915, args->size,
                          ext_data.placements,
                          ext_data.n_placements,



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