[PATCH v2] drm/amdgpu: use drm_gem_ttm_dumb_map_offset() for dumb_map_offset

[saad <primecoder8@gmail.com>]

As part of the DRM TODO item "Remove custom dumb_map_offset
implementations", switch amdgpu's &drm_driver.dumb_map_offset callback
from the driver-specific amdgpu_mode_dumb_mmap() to the generic TTM
helper drm_gem_ttm_dumb_map_offset(), for both amdgpu_kms_driver and
amdgpu_partition_driver.

amdgpu_mode_dumb_mmap() additionally rejected userptr BOs and BOs
created with AMDGPU_GEM_CREATE_NO_CPU_ACCESS with -EPERM. Dropping
those checks from the dumb path does not allow such BOs to be mapped:
returning an offset does not create a mapping, and the actual mmap()
goes through drm_gem_mmap() -> amdgpu_gem_object_mmap(), which performs
the same two checks and still returns -EPERM. The only user-visible
difference is that DRM_IOCTL_MODE_MAP_DUMB on such a handle now succeeds
and the subsequent mmap() fails, instead of the ioctl failing. Dumb
buffers created by amdgpu_mode_dumb_create() are never userptr BOs and
always have AMDGPU_GEM_CREATE_CPU_ACCESS_REQUIRED set, so they are not
affected.

With that, amdgpu_gem_mmap_ioctl() is the only remaining user of
amdgpu_mode_dumb_mmap(), so fold it into the ioctl and drop its
prototype from amdgpu_gem.h. DRM_IOCTL_AMDGPU_GEM_MMAP, used by
libdrm_amdgpu and Mesa, keeps the userptr and NO_CPU_ACCESS checks
and behaves as before.

Build-tested with CONFIG_DRM_AMDGPU=m (W=1 for amdgpu_drv.o and
amdgpu_gem.o), no new warnings. Not runtime tested.

The code change was written by hand and reviewed with the help of
Claude (AI coding assistant); the commit message was written by Claude.

Signed-off-by: saad <primecoder8@gmail.com>
---
Changes in v2:
- Fold amdgpu_mode_dumb_mmap() into amdgpu_gem_mmap_ioctl() and drop its
  prototype, as it has no other users (Sashiko)
- Link to v1: https://lore.kernel.org/r/20261105-amdgpu-dumb-map-offset-v1-1-7299d94ede11@gmail.com
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c |  5 +++--
 drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c | 23 +++++++++--------------
 drivers/gpu/drm/amd/amdgpu/amdgpu_gem.h |  3 ---
 3 files changed, 12 insertions(+), 19 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
index 731fe8f9e..134d2fe4b 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
@@ -27,6 +27,7 @@
 #include <drm/drm_drv.h>
 #include <drm/drm_fbdev_ttm.h>
 #include <drm/drm_gem.h>
+#include <drm/drm_gem_ttm_helper.h>
 #include <drm/drm_managed.h>
 #include <drm/drm_pciids.h>
 #include <drm/drm_probe_helper.h>
@@ -3151,7 +3152,7 @@ static const struct drm_driver amdgpu_kms_driver = {
 	.ioctls = amdgpu_ioctls_kms,
 	.num_ioctls = ARRAY_SIZE(amdgpu_ioctls_kms),
 	.dumb_create = amdgpu_mode_dumb_create,
-	.dumb_map_offset = amdgpu_mode_dumb_mmap,
+	.dumb_map_offset = drm_gem_ttm_dumb_map_offset,
 	DRM_FBDEV_TTM_DRIVER_OPS,
 	.fops = &amdgpu_driver_kms_fops,
 	.release = &amdgpu_driver_release_kms,
@@ -3177,7 +3178,7 @@ const struct drm_driver amdgpu_partition_driver = {
 	.ioctls = amdgpu_ioctls_kms,
 	.num_ioctls = ARRAY_SIZE(amdgpu_ioctls_kms),
 	.dumb_create = amdgpu_mode_dumb_create,
-	.dumb_map_offset = amdgpu_mode_dumb_mmap,
+	.dumb_map_offset = drm_gem_ttm_dumb_map_offset,
 	DRM_FBDEV_TTM_DRIVER_OPS,
 	.fops = &amdgpu_driver_kms_fops,
 	.release = &amdgpu_driver_release_kms,
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
index 4ed1706d8..2a72bdf2d 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
@@ -644,13 +644,16 @@ int amdgpu_gem_userptr_ioctl(struct drm_device *dev, void *data,
 	return r;
 }
 
-int amdgpu_mode_dumb_mmap(struct drm_file *filp,
-			  struct drm_device *dev,
-			  uint32_t handle, uint64_t *offset_p)
+int amdgpu_gem_mmap_ioctl(struct drm_device *dev, void *data,
+			  struct drm_file *filp)
 {
+	union drm_amdgpu_gem_mmap *args = data;
+	uint32_t handle = args->in.handle;
 	struct drm_gem_object *gobj;
 	struct amdgpu_bo *robj;
 
+	memset(args, 0, sizeof(*args));
+
 	gobj = drm_gem_object_lookup(filp, handle);
 	if (!gobj)
 		return -ENOENT;
@@ -661,19 +664,11 @@ int amdgpu_mode_dumb_mmap(struct drm_file *filp,
 		drm_gem_object_put(gobj);
 		return -EPERM;
 	}
-	*offset_p = amdgpu_bo_mmap_offset(robj);
-	drm_gem_object_put(gobj);
-	return 0;
-}
 
-int amdgpu_gem_mmap_ioctl(struct drm_device *dev, void *data,
-			  struct drm_file *filp)
-{
-	union drm_amdgpu_gem_mmap *args = data;
-	uint32_t handle = args->in.handle;
+	args->out.addr_ptr = amdgpu_bo_mmap_offset(robj);
+	drm_gem_object_put(gobj);
 
-	memset(args, 0, sizeof(*args));
-	return amdgpu_mode_dumb_mmap(filp, dev, handle, &args->out.addr_ptr);
+	return 0;
 }
 
 /**
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.h b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.h
index b558336bc..718ffe229 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.h
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.h
@@ -49,9 +49,6 @@ int amdgpu_gem_object_create(struct amdgpu_device *adev, unsigned long size,
 int amdgpu_mode_dumb_create(struct drm_file *file_priv,
 			    struct drm_device *dev,
 			    struct drm_mode_create_dumb *args);
-int amdgpu_mode_dumb_mmap(struct drm_file *filp,
-			  struct drm_device *dev,
-			  uint32_t handle, uint64_t *offset_p);
 
 int amdgpu_gem_create_ioctl(struct drm_device *dev, void *data,
 			    struct drm_file *filp);

---
base-commit: 279235273fc6c0a33df863b4a1cc52ec1e73aba5
change-id: 20261105-amdgpu-dumb-map-offset-6fa41e8d3fb5

Best regards,
-- 
saad <primecoder8@gmail.com>