在 2026-02-25三的 09:34 +0100，Thomas Zimmermann写道： > Hi > > Am 25.02.26 um 09:10 schrieb Icenowy Zheng: > > 在 2026-02-25三的 08:47 +0100，Thomas Zimmermann写道： > > > > > > Am 25.02.26 um 08:38 schrieb Icenowy Zheng: > > > > 在 2026-02-25三的 08:26 +0100，Thomas Zimmermann写道： > > > > > 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. > > > > Yes, I saw this piece of document; however it's part of the > > > > interface > > > > document instead of a concept document, and the whole existence > > > > of > > > > the > > > What is a concept document? > > Well I am patching this document snippet because it becomes part of > > the > > document at [1] (by being referenced in the .rst file). > > That question was a joke, but also not entirely untrue. > > These overview sections usually introduce the purpose of a module and > give readers a sense of how to use the code; like a tutorial. We > don't > have concept documents. As the concepts keep changing, they'd bitrot > quickly. > > For example, not too long ago we discussed the possibility of a > CREATE_DUMB2 ioctl that would allow for specifying the DRM format > directly. It would also allow formats with multiple planes and > non-linear layouts. My point is that whatever we write here today > could > be obsolete tomorrow. The only stable thing is the user-space > interfaces. > > IMHO if you think the overview should mention the supported formats, > you > should link to the UAPI documentation of the ioctl. If we ever get > that > CREATE2 ioctl, we can refer to this as well.
This sounds reasonable. I will reword this to a reference to the UAPI documentation to raise attraction (because otherwise it's not very natrual to consult the UAPI doc, at least for me). Thanks, Icenowy > > Best regards > Thomas > > > > > [1] https://docs.kernel.org/gpu/drm-kms.html#dumb-buffer-objects > > > > > > document snippet I am changing can be considered a duplicate of > > > > the > > > > interface document. > > > > > > > > Thanks > > > > Icenowy > > > > > > > > > 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,
