Re: [PATCH 1/2] drm/i915/joiner: Make joiner "nomodeset" state copy independent of pipe order

[Jani Nikula <jani.nikula@intel.com>]

On Wed, 08 Apr 2026, Ville Syrjala <ville.syrjala@linux.intel.com> wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
>
> Currently the joiner primary->secondary hw state copy still happens from
> the main compute_config loop alongside the primary uapi->hw state copy.
> The primary uapi->hw state copy must therefore happen first, or else
> we'll end up copying stale junk into the secondary.
>
> We have a WARN in intel_atomic_check_joiner() to make sure the CRTCs
> will be walked in the correct order. The plan is to reoder the CRTCs,
> which would mess up the order, unless we also adjust the iterators
> to keep the pipe order. The actual plan is to do both, so technically
> we should be able to just remove the WARN and call it a day.
>
> But relying on the iteration order like this is fragile and confusing,
> so let's move the "nomodeset" joiner state copy into the later loop
> where the "modeset" state copy is also done. The first loop having
> completely finished, we are guaranteed to have up to date hw state
> on the primary when we do the copy to the secondary.

I find the number of loops in the forest of intel_atomic_check*
functions confusing too. But this looks like progress.

Reviewed-by: Jani Nikula <jani.nikula@intel.com>

I'm wondering about merging this, along with the pipe reordering, to a
topic branch that could be merged to drm-next at Dave's discretion,
instead of cherry-picks which might be a bit cumbersome for patches this
size. So please hold off on merging while I figure this out.


>
> Cc: Jani Nikula <jani.nikula@intel.com>
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_display.c | 20 +++++---------------
>  1 file changed, 5 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
> index 58a654ca0d20..674a4ece6d0f 100644
> --- a/drivers/gpu/drm/i915/display/intel_display.c
> +++ b/drivers/gpu/drm/i915/display/intel_display.c
> @@ -5914,17 +5914,6 @@ static int intel_atomic_check_joiner(struct intel_atomic_state *state,
>  			return -EINVAL;
>  		}
>  
> -		/*
> -		 * The state copy logic assumes the primary crtc gets processed
> -		 * before the secondary crtc during the main compute_config loop.
> -		 * This works because the crtcs are created in pipe order,
> -		 * and the hardware requires primary pipe < secondary pipe as well.
> -		 * Should that change we need to rethink the logic.
> -		 */
> -		if (WARN_ON(drm_crtc_index(&primary_crtc->base) >
> -			    drm_crtc_index(&secondary_crtc->base)))
> -			return -EINVAL;
> -
>  		drm_dbg_kms(display->drm,
>  			    "[CRTC:%d:%s] Used as secondary for joiner primary [CRTC:%d:%s]\n",
>  			    secondary_crtc->base.base.id, secondary_crtc->base.name,
> @@ -6302,9 +6291,7 @@ static int intel_atomic_check_config(struct intel_atomic_state *state,
>  
>  	for_each_new_intel_crtc_in_state(state, crtc, new_crtc_state, i) {
>  		if (!intel_crtc_needs_modeset(new_crtc_state)) {
> -			if (intel_crtc_is_joiner_secondary(new_crtc_state))
> -				copy_joiner_crtc_state_nomodeset(state, crtc);
> -			else
> +			if (!intel_crtc_is_joiner_secondary(new_crtc_state))
>  				intel_crtc_copy_uapi_to_hw_state_nomodeset(state, crtc);
>  			continue;
>  		}
> @@ -6439,8 +6426,11 @@ int intel_atomic_check(struct drm_device *dev,
>  		goto fail;
>  
>  	for_each_new_intel_crtc_in_state(state, crtc, new_crtc_state, i) {
> -		if (!intel_crtc_needs_modeset(new_crtc_state))
> +		if (!intel_crtc_needs_modeset(new_crtc_state)) {
> +			if (intel_crtc_is_joiner_secondary(new_crtc_state))
> +				copy_joiner_crtc_state_nomodeset(state, crtc);
>  			continue;
> +		}
>  
>  		if (intel_crtc_is_joiner_secondary(new_crtc_state)) {
>  			drm_WARN_ON(display->drm, new_crtc_state->uapi.enable);

-- 
Jani Nikula, Intel