Re: [PATCH] drm/msm: restore GEM-related IOCTLs for KMS devices

[Dmitry Baryshkov]

On Wed, Mar 04, 2026 at 06:59:42AM -0800, Rob Clark wrote:
> On Wed, Mar 4, 2026 at 6:57 AM Rob Clark <rob.clark@xxxxxxxxxxxxxxxx> wrote:
> >
> > On Wed, Mar 4, 2026 at 5:34 AM Dmitry Baryshkov
> > <dmitry.baryshkov@xxxxxxxxxxxxxxxx> wrote:
> > >
> > > The MSM GBM backend uses MSM_GEM_NEW to allocate GEM buffers from the
> > > KMS driver, imports them into the GPU driver (msm or kgsl) and then
> > > uses them for rendering / blending. Commit 98f11fd1cf92 ("drm/msm: Take
> > > the ioctls away from the KMS-only driver") dropped all IOCTLs from the
> > > MSM KMS devices, pointing out the need to use dumb buffers, however dumb
> > > buffers should not be used by the GPU for rendering. Restore GEM-related
> > > IOCTLs for the KMS devices.
> > >
> > > Fixes: 98f11fd1cf92 ("drm/msm: Take the ioctls away from the KMS-only driver")
> > > Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxxxxxxxx>
> > > ---
> > > Note, here I assume that dumb buffers generally should not be used for
> > > rendering. That doesn't seem to be complete truth as Mesa kmsro on MSM
> > > devices uses DRM_IOCTL_MODE_CREATE_DUMB to create buffers for resources.
> >
> > That is problematic in kmsro.. (but also unsure to what degree kmsro
> > ever got used "in production".. the x86 drivers don't use it.  Android
> > and chromeos didn't use it.  Etc.)
> 
> (also, allocate from the gpu render node)

I think Asahi and VC4 allocate buffers from the GPU node and then import
them on the render side, but unfortunately iMX IPU driver doesn't seem
to support PRIME_FD_TO_HANDLE.

-- 
With best wishes
Dmitry