On Fri, Nov 15, 2019 at 09:42:03PM +0200, Ville Syrjala wrote:
> From: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
>
> The early return in drm_atomic_set_mode_for_crtc() isn't quite
> right. It would mistakenly return and fail to update
> crtc_state->enable if someone actually tried to set a zeroed
> mode on a currently disabled crtc. That should never actually
> happen in response to any userspace request as the zeroed mode
> would get rejected earlier. However there is some chance of this
> happening internally (eg. during hw state readout) so it seems
> best to not let the state become totally inconsistent.
>
> Additionally the early return will not be taken if we're trying to
> disable an already disabled crtc. While that is not actually
> harmful it is inconsistent, so let's handle that case as well.
>
> Testcase: igt/kms_selftest/check_atomic_set_mode_for_crtc
> Testcase: igt/kms_selftest/check_atomic_set_zeroed_mode_fort_crtc
> Reviewed-by: Daniel Vetter <daniel@xxxxxxxx>
> Signed-off-by: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
> ---
> drivers/gpu/drm/drm_atomic_uapi.c | 9 +++++++--
> 1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_atomic_uapi.c b/drivers/gpu/drm/drm_atomic_uapi.c
> index 0d466d3b0809..a3a6a8137af4 100644
> --- a/drivers/gpu/drm/drm_atomic_uapi.c
> +++ b/drivers/gpu/drm/drm_atomic_uapi.c
> @@ -68,8 +68,13 @@ int drm_atomic_set_mode_for_crtc(struct drm_crtc_state *state,
> struct drm_mode_modeinfo umode;
>
> /* Early return for no change. */
> - if (mode && memcmp(&state->mode, mode, sizeof(*mode)) == 0)
> - return 0;
> + if (state->enable) {
Hm I think this would be clearer if you go with
if (state->enable == !!mode &&
(!mode || memcmp(&state->mode, mode, sizeof(*mode)) == 0))
return 0;
But also somewhat a bikeshed. I'm also wondering whether we shouldn't just
declare this a driver bug (it means enable and mode are already out of
sync), but I guess hw state readout is special sometimes.
Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
> + if (mode && memcmp(&state->mode, mode, sizeof(*mode)) == 0)
> + return 0;
> + } else {
> + if (!mode)
> + return 0;
> + }
>
> drm_property_blob_put(state->mode_blob);
> state->mode_blob = NULL;
> --
> 2.23.0
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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