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

[Rob Clark <rob.clark@oss.qualcomm.com>]

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.

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
>