Hi,
Am 25.02.26 um 07:13 schrieb Icenowy Zheng:
The ioctl interfaces for dumb buffers currently only properly support
linear buffers.
Mention this in the documentation snippet of dumb-buffers source code,
which is referenced by drm-kms.rst and will end up in the built kernel
documentation.
Also mention the existence of current drivers abusing dumb buffers for
AFBC to reduce confusion about this.
Signed-off-by: Icenowy Zheng <[email protected]>
---
drivers/gpu/drm/drm_dumb_buffers.c | 7 ++++++-
We documented the meaning of the color bits and the behavior of the
dumb-buffer interface at [1]. If anything is missing, it should be added
there.
Best regards
Thomas
[1]
https://elixir.bootlin.com/linux/v6.19/source/include/uapi/drm/drm_mode.h#L1200
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/drm_dumb_buffers.c
b/drivers/gpu/drm/drm_dumb_buffers.c
index e2b62e5fb891b..06f74460adf62 100644
--- a/drivers/gpu/drm/drm_dumb_buffers.c
+++ b/drivers/gpu/drm/drm_dumb_buffers.c
@@ -57,7 +57,12 @@
*
* Note that dumb objects may not be used for gpu acceleration, as has been
* attempted on some ARM embedded platforms. Such drivers really must have
- * a hardware-specific ioctl to allocate suitable buffer objects.
+ * a hardware-specific ioctl to allocate suitable buffer objects. They are
+ * also currently meant for only linear buffers, and using them with any
+ * modifier other than DRM_FORMAT_MOD_LINEAR is undefined behavior. There
+ * exist some KMS drivers abusing dumb objects for AFBC framebuffers, but this
+ * behavior is discouraged, only exists as a hack now and shouldn't be
+ * replicated.
*/
static int drm_mode_align_dumb(struct drm_mode_create_dumb *args,
--
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com
GF: Jochen Jaser, Andrew McDonald, Werner Knoblich, (HRB 36809, AG Nürnberg)
