Re: [Intel-gfx] [PATCH 02/26] drm/i915: Do .crtc_compute_clock() earlier

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

On Tue, 03 May 2022, Ville Syrjala <ville.syrjala@linux.intel.com> wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
>
> Currently we calculate a lot of things (pixel rate, watermarks,
> cdclk) trusting that the DPLL can generate the exact frequency
> we ask it. In practice that is not true and there can be
> certain amount of rounding involved.
>
> To allow us to eventually get accurate numbers for all our
> DPLL clock derived state we need to move the DPLL calculation
> to hapen much earlier. To that end we hoist it up to the just
> after the fastset checks. For now we just do the easy code
> motion, and the actual back feeding of the final DPLL clock
> into the state will come later.
>
> A slight change here is that now .crtc_compute_clock()
> can get called while the shared_dpll is still assigned.
> But since .crtc_compute_clock() no longer assignes new
> shared_dplls this is perfectly fine.
>
> TODO: I'd actually like to do this before the fastset check
> so that if the DPLL state should change we actually do the
> modeset. Which I think is what the video aficionados want,
> but it might not be what the fans of fastboot want. Not yet
> sure how to reconcile those conflicting requirements...
>
> v2: s/return/goto/ in error handling
>
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

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

> ---
>  drivers/gpu/drm/i915/display/intel_display.c | 9 +++++----
>  drivers/gpu/drm/i915/display/intel_dpll.c    | 3 ---
>  2 files changed, 5 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
> index 0decf3d24237..5e50e0d56088 100644
> --- a/drivers/gpu/drm/i915/display/intel_display.c
> +++ b/drivers/gpu/drm/i915/display/intel_display.c
> @@ -4905,10 +4905,6 @@ static int intel_crtc_atomic_check(struct intel_atomic_state *state,
>  		crtc_state->update_wm_post = true;
>  
>  	if (mode_changed) {
> -		ret = intel_dpll_crtc_compute_clock(state, crtc);
> -		if (ret)
> -			return ret;
> -
>  		ret = intel_dpll_crtc_get_shared_dpll(state, crtc);
>  		if (ret)
>  			return ret;
> @@ -7801,6 +7797,11 @@ static int intel_atomic_check(struct drm_device *dev,
>  					    new_crtc_state, i) {
>  		if (intel_crtc_needs_modeset(new_crtc_state)) {
>  			any_ms = true;
> +
> +			ret = intel_dpll_crtc_compute_clock(state, crtc);
> +			if (ret)
> +				goto fail;
> +
>  			continue;
>  		}
>  
> diff --git a/drivers/gpu/drm/i915/display/intel_dpll.c b/drivers/gpu/drm/i915/display/intel_dpll.c
> index c19fb075ee6e..7f0538ee2b51 100644
> --- a/drivers/gpu/drm/i915/display/intel_dpll.c
> +++ b/drivers/gpu/drm/i915/display/intel_dpll.c
> @@ -1449,9 +1449,6 @@ int intel_dpll_crtc_compute_clock(struct intel_atomic_state *state,
>  
>  	drm_WARN_ON(&i915->drm, !intel_crtc_needs_modeset(crtc_state));
>  
> -	if (drm_WARN_ON(&i915->drm, crtc_state->shared_dpll))
> -		return 0;
> -
>  	memset(&crtc_state->dpll_hw_state, 0,
>  	       sizeof(crtc_state->dpll_hw_state));

-- 
Jani Nikula, Intel Open Source Graphics Center