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

[Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>]

On Wed, Mar 04, 2026 at 07:57:34AM -0800, Rob Clark wrote:
> On Wed, Mar 4, 2026 at 5:34 AM Dmitry Baryshkov
> <dmitry.baryshkov@oss.qualcomm.com> 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.
> 
> We shouldn't be exposing DRIVER_RENDER on KMS-only nodes.  If msm gbm
> is allocating from a primary node, that is problematic, since there is
> no guarantee that anything but the compositor has access to the
> primary node.

We are not exposing DRIVER_RENDER for KMS-only nodes. I'll check with
the correponding colleagues, what exactly is their use case, if the
allocation is happening in the compositor or in the app. In the latter
case, I agree, the buffers should be allocated from the GPU.

> 
> BR,
> -R
> 
> >
> > Fixes: 98f11fd1cf92 ("drm/msm: Take the ioctls away from the KMS-only driver")
> > Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
> > ---
> > 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.
> > ---
> >  drivers/gpu/drm/msm/msm_drv.c | 10 ++++++++++
> >  1 file changed, 10 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/msm/msm_drv.c b/drivers/gpu/drm/msm/msm_drv.c
> > index ed2a61c66ac9..f82c9a36a166 100644
> > --- a/drivers/gpu/drm/msm/msm_drv.c
> > +++ b/drivers/gpu/drm/msm/msm_drv.c
> > @@ -799,6 +799,14 @@ static const struct drm_ioctl_desc msm_ioctls[] = {
> >         DRM_IOCTL_DEF_DRV(MSM_VM_BIND,      msm_ioctl_vm_bind,      DRM_RENDER_ALLOW),
> >  };
> >
> > +static const struct drm_ioctl_desc msm_kms_ioctls[] = {
> > +       DRM_IOCTL_DEF_DRV(MSM_GEM_NEW,      msm_ioctl_gem_new,      DRM_RENDER_ALLOW),
> > +       DRM_IOCTL_DEF_DRV(MSM_GEM_INFO,     msm_ioctl_gem_info,     DRM_RENDER_ALLOW),
> > +       DRM_IOCTL_DEF_DRV(MSM_GEM_CPU_PREP, msm_ioctl_gem_cpu_prep, DRM_RENDER_ALLOW),
> > +       DRM_IOCTL_DEF_DRV(MSM_GEM_CPU_FINI, msm_ioctl_gem_cpu_fini, DRM_RENDER_ALLOW),
> > +       DRM_IOCTL_DEF_DRV(MSM_GEM_MADVISE,  msm_ioctl_gem_madvise,  DRM_RENDER_ALLOW),
> > +};
> > +
> >  static void msm_show_fdinfo(struct drm_printer *p, struct drm_file *file)
> >  {
> >         struct drm_device *dev = file->minor->dev;
> > @@ -868,6 +876,8 @@ static const struct drm_driver msm_kms_driver = {
> >  #endif
> >         MSM_FBDEV_DRIVER_OPS,
> >         .show_fdinfo        = msm_show_fdinfo,
> > +       .ioctls             = msm_kms_ioctls,
> > +       .num_ioctls         = ARRAY_SIZE(msm_kms_ioctls),
> >         .fops               = &fops,
> >         .name               = "msm-kms",
> >         .desc               = "MSM Snapdragon DRM",
> >
> > ---
> > base-commit: ac47870fd795549f03d57e0879fc730c79119f4b
> > change-id: 20260304-msm-restore-ioctls-2a1792311a09
> >
> > Best regards,
> > --
> > With best wishes
> > Dmitry
> >

-- 
With best wishes
Dmitry