Re: [PATCH 2/4] drm/i915: Fix intel_dp_mst_compute_link_config

["Govindapillai, Vinod" <vinod.govindapillai@intel.com>]

Reviewed-by: Vinod Govindapillai <vinod.govindapillai@intel.com>


On Mon, 2022-08-29 at 12:58 +0300, Stanislav Lisovskiy wrote:
> We currently always exit that bpp loop because drm_dp_atomic_find_vcpi_slots
> doesn't care if we actually can fit those or not.
> I think that wasn't the initial intention here, especially when
> we keep trying with lower bpps, we are supposed to keep trying
> until we actually find some _working_ configuration, which isn't the
> case here.
> So added that drm_dp_mst_check here, so that we can make sure
> that try all the bpps before we fail.
> 
> Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_dp_mst.c | 16 ++++++++++++++--
>  1 file changed, 14 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c
> b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> index 13abe2b2170e..c4f92edbdd08 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> @@ -60,6 +60,7 @@ static int intel_dp_mst_compute_link_config(struct intel_encoder *encoder,
>                 &crtc_state->hw.adjusted_mode;
>         bool constant_n = drm_dp_has_quirk(&intel_dp->desc, DP_DPCD_QUIRK_CONSTANT_N);
>         int bpp, slots = -EINVAL;
> +       int ret = 0;
>  
>         mst_state = drm_atomic_get_mst_topology_state(state, &intel_dp->mst_mgr);
>         if (IS_ERR(mst_state))
> @@ -85,10 +86,21 @@ static int intel_dp_mst_compute_link_config(struct intel_encoder *encoder,
>                                                       connector->port, crtc_state->pbn);
>                 if (slots == -EDEADLK)
>                         return slots;
> -               if (slots >= 0)
> -                       break;
> +               if (slots >= 0) {
> +                       ret = drm_dp_mst_atomic_check(state);
> +                       /*
> +                        * If we got slots >= 0 and we can fit those based on check
> +                        * then we can exit the loop. Otherwise keep trying.
> +                        */
> +                       if (!ret)
> +                               break;
> +               }
>         }
>  
> +       /* Despite slots are non-zero, we still failed the atomic check */
> +       if (ret && slots >= 0)
> +               slots = ret;
> +
>         if (slots < 0) {
>                 drm_dbg_kms(&i915->drm, "failed finding vcpi slots:%d\n",
>                             slots);