Re: [PATCH] drm/i915/gem/mman: only allow WC for lmem

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On 02/06/2021 13:00, Thomas Hellström wrote:
Hi,

On 6/2/21 11:36 AM, Matthew Auld wrote:
For dgfx where we now have lmem and ttm, we can only support single mmap
mode for the lifetime of the object, and for lmem objects this should be
WC, so reject all other mapping modes for mmap_offset, including if the
object can be placed in both smem and lmem.

Signed-off-by: Matthew Auld <matthew.auld@xxxxxxxxx>
Cc: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>
Cc: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
---
  drivers/gpu/drm/i915/gem/i915_gem_mman.c   |  4 ++++
  drivers/gpu/drm/i915/gem/i915_gem_object.c | 22 ++++++++++++++++++++++
  drivers/gpu/drm/i915/gem/i915_gem_object.h |  4 ++++
  3 files changed, 30 insertions(+)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_mman.c b/drivers/gpu/drm/i915/gem/i915_gem_mman.c
index fd1c9714f8d8..32f88f236771 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_mman.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_mman.c
@@ -689,6 +689,10 @@ __assign_mmap_offset(struct drm_file *file,
          goto out;
      }
+    if (mmap_type != I915_MMAP_TYPE_WC &&
+        i915_gem_object_placements_contain_type(obj, INTEL_MEMORY_LOCAL))
+        return -ENODEV;
+

I think we will also have the restriction that any other objects on DGFX can only be mapped cached? At least that's what the TTM code is implementing currently.

Yeah, with this patch the caching mode should now at least be consistent for lmem objects, for smem we still need more patches.



      mmo = mmap_offset_attach(obj, mmap_type, file);
      if (IS_ERR(mmo)) {
          err = PTR_ERR(mmo);
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.c b/drivers/gpu/drm/i915/gem/i915_gem_object.c
index 2be6109d0093..d4b0da8ed969 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_object.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_object.c
@@ -403,6 +403,28 @@ int i915_gem_object_read_from_page(struct drm_i915_gem_object *obj, u64 offset,
      return 0;
  }
+/**
+ * i915_gem_object_placements_contain_type - Check whether the object can be
+ * placed at certain memory type
+ * @obj: Pointer to the object
+ * @type: The memory type to check
+ *
+ * Return: True if the object can be placed in @type. False otherwise.
+ */
+bool i915_gem_object_placements_contain_type(struct drm_i915_gem_object *obj,
+                         enum intel_memory_type type)
+{
+    unsigned int i;
+
+    /* TODO: consider maybe storing as a mask when doing gem_create_ext */
+    for (i = 0; i < obj->mm.n_placements; i++) {
+        if (obj->mm.placements[i]->type == type)
+            return true;
+    }
+
+    return false;
+}
+

Do we need something for the in-kernel mappings as well? Or just return a mapping with the only allowed caching mode?

For lmem everything should already be WC for in-kernel mappings. For everything else which uses pin_map() we will need to default to cached. I guess just add a different helper for this? We should probably also adjust the obj->cache_level for dg1.


/Thomas


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