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.
>
> 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.

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.)

BR,
-R

> ---
>  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
>