[PATCH] drm/atomic: Add the crtc to affected crtc only if uapi.enable = true

[Pekka Paalanen]

On Tue,  2 Mar 2021 12:41:32 -0800
Manasi Navare <manasi.d.navare at intel.com> wrote:

> In case of a modeset where a mode gets split across mutiple CRTCs
> in the driver specific implementation (bigjoiner in i915) we wrongly count
> the affected CRTCs based on the drm_crtc_mask and indicate the stolen CRTC as
> an affected CRTC in atomic_check_only().
> This triggers a warning since affected CRTCs doent match requested CRTC.
> 
> To fix this in such bigjoiner configurations, we should only
> increment affected crtcs if that CRTC is enabled in UAPI not
> if it is just used internally in the driver to split the mode.

Hi,

I think that makes sense to me. Stealing CRTCs that are not currently
used by the userspace (display server) should be ok, as long as that
is completely invisible to userspace: meaning that it does not cause
userspace to unexpectedly e.g. receive or miss per-crtc atomic
completion events.

Can that also be asserted somehow, or does this already do that?


Thanks,
pq

> Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> Cc: Simon Ser <contact at emersion.fr>
> Cc: Pekka Paalanen <pekka.paalanen at collabora.co.uk>
> Cc: Daniel Stone <daniels at collabora.com>
> Cc: Daniel Vetter <daniel.vetter at intel.com>
> Cc: dri-devel at lists.freedesktop.org
> Signed-off-by: Manasi Navare <manasi.d.navare at intel.com>
> ---
>  drivers/gpu/drm/drm_atomic.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
> index 5b4547e0f775..d7acd6bbd97e 100644
> --- a/drivers/gpu/drm/drm_atomic.c
> +++ b/drivers/gpu/drm/drm_atomic.c
> @@ -1358,8 +1358,10 @@ int drm_atomic_check_only(struct drm_atomic_state *state)
>  		}
>  	}
>  
> -	for_each_new_crtc_in_state(state, crtc, new_crtc_state, i)
> -		affected_crtc |= drm_crtc_mask(crtc);
> +	for_each_new_crtc_in_state(state, crtc, new_crtc_state, i) {
> +		if (new_crtc_state->enable)
> +			affected_crtc |= drm_crtc_mask(crtc);
> +	}
>  
>  	/*
>  	 * For commits that allow modesets drivers can add other CRTCs to the

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