Re: [Intel-gfx] [PATCH] drm/i915: Don't oops in dumb_create ioctl if we have no crtcs

[Chris Wilson <chris@chris-wilson.co.uk>]

Quoting Ville Syrjala (2019-11-06 17:23:49)
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> 
> Make sure we have a crtc before probing its primary plane's
> max stride. Initially I thought we can't get this far without
> crtcs, but looks like we can via the dumb_create ioctl.
> 
> Not sure if we shouldn't disable dumb buffer support entirely
> when we have no crtcs, but that would require some amount of work
> as the only thing currently being checked is dev->driver->dumb_create
> which we'd have to convert to some device specific dynamic thing.
> 
> Cc: stable@vger.kernel.org
> Reported-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
> Fixes: aa5ca8b7421c ("drm/i915: Align dumb buffer stride to 4k to allow for gtt remapping")
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_display.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
> index 1f93860fb897..331030765ca9 100644
> --- a/drivers/gpu/drm/i915/display/intel_display.c
> +++ b/drivers/gpu/drm/i915/display/intel_display.c
> @@ -2543,6 +2543,9 @@ u32 intel_plane_fb_max_stride(struct drm_i915_private *dev_priv,
>          * the highest stride limits of them all.
>          */
>         crtc = intel_get_crtc_for_pipe(dev_priv, PIPE_A);
> +       if (!crtc)
> +               return 0;
> +

Callers:
intel_fb_max_stride -> intel_framebuffer_init, not used if no display
intel_fb_stride_alignment,
	0 -> intel_tile_size() alignment. ok ->
	intel_framebuffer_init, not used as no display

-> i915_gem_dumb_create -> args->pitch = PAGE_ALIGN()

Ok, not as horrible as I feared when I saw return 0 from max_stride!

Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
-Chris