Re: [RFC PATCH v3 2/2] drm/i915/display: Synchronize crtc_state for initial commit

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

On Wed, 21 Jan 2026, Juasheem Sultan <jdsultan@google.com> wrote:
> When attempting the initial commit, there is a mismatch between
> the new crtc_state and the old crtc_state. This causes us to fail the
> pipe_config comparison and force a modeset. In the case where we are
> inheriting an initialized state, we can sync the new and the old state
> to pass the comparison and allow us to do a fastset and achieve an
> uninterrupted handoff to userspace.
>
> Signed-off-by: Juasheem Sultan <jdsultan@google.com>
> ---
>  drivers/gpu/drm/i915/display/intel_display.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
> index 0d527cf22866..6eef4bd2e251 100644
> --- a/drivers/gpu/drm/i915/display/intel_display.c
> +++ b/drivers/gpu/drm/i915/display/intel_display.c
> @@ -5736,6 +5736,25 @@ static void intel_crtc_check_fastset(const struct intel_crtc_state *old_crtc_sta
>  	if (old_crtc_state->vrr.in_range != new_crtc_state->vrr.in_range)
>  		new_crtc_state->update_lrr = false;
>  
> +	/* Copying crtc state if inheriting an old state for commit */
> +	if (old_crtc_state->inherited) {
> +		new_crtc_state->hw = old_crtc_state->hw;
> +
> +		new_crtc_state->port_clock = old_crtc_state->port_clock;
> +		new_crtc_state->pipe_bpp = old_crtc_state->pipe_bpp;
> +		new_crtc_state->cpu_transcoder = old_crtc_state->cpu_transcoder;
> +		new_crtc_state->lane_count = old_crtc_state->lane_count;
> +		new_crtc_state->output_types = old_crtc_state->output_types;
> +		new_crtc_state->dp_m_n = old_crtc_state->dp_m_n;
> +		new_crtc_state->framestart_delay = old_crtc_state->framestart_delay;
> +		new_crtc_state->pixel_multiplier = old_crtc_state->pixel_multiplier;
> +		new_crtc_state->pixel_rate = old_crtc_state->pixel_rate;
> +		new_crtc_state->enhanced_framing = old_crtc_state->enhanced_framing;
> +		new_crtc_state->dpll_hw_state = old_crtc_state->dpll_hw_state;
> +		new_crtc_state->intel_dpll = old_crtc_state->intel_dpll;
> +		new_crtc_state->vrr.guardband = old_crtc_state->vrr.guardband;

I'd like to see logs of what the differences are.

BR,
Jani.

> +	}
> +
>  	if (!intel_pipe_config_compare(old_crtc_state, new_crtc_state, true)) {
>  		drm_dbg_kms(display->drm, "[CRTC:%d:%s] fastset requirement not met, forcing full modeset\n",
>  			    crtc->base.base.id, crtc->base.name);

-- 
Jani Nikula, Intel