Re: [PATCH 6/8] drm/i915: Allow fastboot to fix up the vblank delay

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

On Thu, 16 Jan 2025, Ville Syrjala <ville.syrjala@linux.intel.com> wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
>
> GOP might not agree with our idea of what the vblank delay should be.
> Reuse the LRR codepaths to fix that up via a fastset.
>
> The relevant registers aren't actually double buffered so this is a
> little bit dodgy. While I've not seen any real issues from frobbing
> these live, let's limit this to just the fastboot case (by only
> allowing it when old_crtc_state->inherited==true).
>
> Cc: Paz Zcharya <pazz@chromium.org>
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_display.c | 26 +++++++++++++++++---
>  1 file changed, 22 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
> index 9b42d980ed7e..471fe7d80f30 100644
> --- a/drivers/gpu/drm/i915/display/intel_display.c
> +++ b/drivers/gpu/drm/i915/display/intel_display.c
> @@ -5358,6 +5358,19 @@ pipe_config_cx0pll_mismatch(struct drm_printer *p, bool fastset,
>  	intel_cx0pll_dump_hw_state(display, b);
>  }
>  
> +static bool allow_vblank_delay_fastset(const struct intel_crtc_state *old_crtc_state)
> +{
> +	struct intel_display *display = to_intel_display(old_crtc_state);
> +
> +	/*
> +	 * Allow fastboot to fix up vblank delay (handled via LRR
> +	 * codepaths), a bit dodgy as the registers aren't
> +	 * double buffered but seems to be working more or less...
> +	 */
> +	return HAS_LRR(display) && old_crtc_state->inherited &&
> +		!intel_crtc_has_type(old_crtc_state, INTEL_OUTPUT_DSI);
> +}
> +
>  bool
>  intel_pipe_config_compare(const struct intel_crtc_state *current_config,
>  			  const struct intel_crtc_state *pipe_config,
> @@ -5490,7 +5503,8 @@ intel_pipe_config_compare(const struct intel_crtc_state *current_config,
>  	PIPE_CONF_CHECK_I(name.crtc_hsync_start); \
>  	PIPE_CONF_CHECK_I(name.crtc_hsync_end); \
>  	PIPE_CONF_CHECK_I(name.crtc_vdisplay); \
> -	PIPE_CONF_CHECK_I(name.crtc_vblank_start); \
> +	if (!fastset || !allow_vblank_delay_fastset(current_config)) \
> +		PIPE_CONF_CHECK_I(name.crtc_vblank_start); \

Side note, part of me wants to change fastset to some variation of "full
modeset" because *all* the compare checks are for !fastset.

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

>  	PIPE_CONF_CHECK_I(name.crtc_vsync_start); \
>  	PIPE_CONF_CHECK_I(name.crtc_vsync_end); \
>  	if (!fastset || !pipe_config->update_lrr) { \
> @@ -6084,7 +6098,8 @@ static int intel_modeset_checks(struct intel_atomic_state *state)
>  static bool lrr_params_changed(const struct drm_display_mode *old_adjusted_mode,
>  			       const struct drm_display_mode *new_adjusted_mode)
>  {
> -	return old_adjusted_mode->crtc_vblank_end != new_adjusted_mode->crtc_vblank_end ||
> +	return old_adjusted_mode->crtc_vblank_start != new_adjusted_mode->crtc_vblank_start ||
> +		old_adjusted_mode->crtc_vblank_end != new_adjusted_mode->crtc_vblank_end ||
>  		old_adjusted_mode->crtc_vtotal != new_adjusted_mode->crtc_vtotal;
>  }
>  
> @@ -6098,11 +6113,14 @@ 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;
>  
> -	if (!intel_pipe_config_compare(old_crtc_state, new_crtc_state, true))
> +	if (!intel_pipe_config_compare(old_crtc_state, new_crtc_state, true)) {
>  		drm_dbg_kms(&i915->drm, "[CRTC:%d:%s] fastset requirement not met, forcing full modeset\n",
>  			    crtc->base.base.id, crtc->base.name);
> -	else
> +	} else {
> +		if (allow_vblank_delay_fastset(old_crtc_state))
> +			new_crtc_state->update_lrr = true;
>  		new_crtc_state->uapi.mode_changed = false;
> +	}
>  
>  	if (intel_compare_link_m_n(&old_crtc_state->dp_m_n,
>  				   &new_crtc_state->dp_m_n))

-- 
Jani Nikula, Intel