Re: [Intel-gfx] [PATCH v2 2/6] drm/i915: Fix bw atomic check when switching between SAGV vs. no SAGV

["Lisovskiy, Stanislav" <stanislav.lisovskiy@intel.com>]

On Wed, Feb 16, 2022 at 07:42:46PM +0200, Ville Syrjala wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> 
> If the only thing that is changing is SAGV vs. no SAGV but
> the number of active planes and the total data rates end up
> unchanged we currently bail out of intel_bw_atomic_check()
> early and forget to actually compute the new WGV point
> mask and thus won't actually enable/disable SAGV as requested.
> This ends up poorly if we end up running with SAGV enabled
> when we shouldn't. Usually ends up in underruns.
> To fix this let's go through the QGV point mask computation
> if anyone else already added the bw state for us.
> 
> Cc: stable@vger.kernel.org
> Cc: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
> Fixes: 20f505f22531 ("drm/i915: Restrict qgv points which don't have enough bandwidth.")
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>


Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>

> ---
>  drivers/gpu/drm/i915/display/intel_bw.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_bw.c b/drivers/gpu/drm/i915/display/intel_bw.c
> index 23aa8e06de18..d72ccee7d53b 100644
> --- a/drivers/gpu/drm/i915/display/intel_bw.c
> +++ b/drivers/gpu/drm/i915/display/intel_bw.c
> @@ -846,6 +846,13 @@ int intel_bw_atomic_check(struct intel_atomic_state *state)
>  	if (num_psf_gv_points > 0)
>  		mask |= REG_GENMASK(num_psf_gv_points - 1, 0) << ADLS_PSF_PT_SHIFT;
>  
> +	/*
> +	 * If we already have the bw state then recompute everything
> +	 * even if pipe data_rate / active_planes didn't change.
> +	 * Other things (such as SAGV) may have changed.
> +	 */
> +	new_bw_state = intel_atomic_get_new_bw_state(state);
> +
>  	for_each_oldnew_intel_crtc_in_state(state, crtc, old_crtc_state,
>  					    new_crtc_state, i) {
>  		unsigned int old_data_rate =
> -- 
> 2.34.1
>