linux-kernel - Re: [PATCH v1 2/3] drm/msm/dp: decoupling dp->id out of dp controller_id at scxxxx_dp

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Date:   Sat, 25 Jun 2022 02:25:04 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Kuogee Hsieh <quic_khsieh@...cinc.com>
Cc:     Stephen Boyd <swboyd@...omium.org>, agross@...nel.org,
        airlied@...ux.ie, bjorn.andersson@...aro.org, daniel@...ll.ch,
        dianders@...omium.org, dri-devel@...ts.freedesktop.org,
        robdclark@...il.com, sean@...rly.run, vkoul@...nel.org,
        quic_abhinavk@...cinc.com, quic_aravindh@...cinc.com,
        quic_sbillaka@...cinc.com, freedreno@...ts.freedesktop.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 2/3] drm/msm/dp: decoupling dp->id out of dp
 controller_id at scxxxx_dp_cfg table

On Sat, 25 Jun 2022 at 00:17, Kuogee Hsieh <quic_khsieh@...cinc.com> wrote:
>
>
> On 6/24/2022 1:00 PM, Stephen Boyd wrote:
> > Quoting Kuogee Hsieh (2022-06-24 10:15:11)
> >> Current the index (dp->id) of DP descriptor table (scxxxx_dp_cfg[]) are tightly
> >> coupled with DP controller_id. This means DP use controller id 0 must be placed
> >> at first entry of DP descriptor table (scxxxx_dp_cfg[]). Otherwise the internal
> >> INTF will mismatch controller_id. This will cause controller kickoff wrong
> >> interface timing engine and cause dpu_encoder_phys_vid_wait_for_commit_done
> >> vblank timeout error.
> >>
> >> This patch add controller_id field into struct msm_dp_desc to break the tightly
> >> coupled relationship between index (dp->id) of DP descriptor table with DP
> >> controller_id.
> > Please no. This reverts the intention of commit bb3de286d992
> > ("drm/msm/dp: Support up to 3 DP controllers")
> >
> >      A new enum is introduced to document the connection between the
> >      instances referenced in the dpu_intf_cfg array and the controllers in
> >      the DP driver and sc7180 is updated.
> >
> > It sounds like the intent of that commit failed to make a strong enough
> > connection. Now it needs to match the INTF number as well? I can't
> > really figure out what is actually wrong, because this patch undoes that
> > intentional tight coupling. Is the next patch the important part that
> > flips the order of the two interfaces?
>
> The commit bb3de286d992have two problems,
>
> 1)  The below sc7280_dp_cfg will not work, if eDP use
> MSM_DP_CONTROLLER_2 instead of  MSM_DP_CONTROLLER_1
>
> since it have num_descs =2 but eDP is at index 2 (CONTROLLER_2) which
> never be reached.
>
> static const struct msm_dp_config sc7280_dp_cfg = {
>          .descs = (const struct msm_dp_desc[]) {
>                  [MSM_DP_CONTROLLER_2] = { .io_start = 0x0aea0000,
> .connector_type = DRM_MODE_CONNECTOR_eDP, .wide_bus_en = true },
>                  [MSM_DP_CONTROLLER_0] = { .io_start = 0x0ae90000,
> .connector_type = DRM_MODE_CONNECTOR_DisplayPort, .wide_bus_en = true },
>          },
>          .num_descs = 2,

Please change num_descs to 3. Or better eliminate it completely and
iterate up to MSM_DP_CONTROLLER_MAX, checking whether the entry
contains real values or is just a zero sentinel entry.

> };
>
> 2)  DP always has index of 0 (dp->id = 0) and the first one to call
> msm_dp_modeset_init(). This make DP always place at head of bridge chain.
>
> At next patch eDP must be placed at head of bridge chain to fix eDP
> corruption issue. This is the purpose of this patch. I will revise the
> commit text.

This text doesn't make sense to me. The dp->id has nothing to do with
the bridge chains. Each dp entry is a head of the corresponding bridge
chain. DP with dp->id = 0 and eDP with dp->id = whatever will be parts
of different encoder -> bridges -> connector chains.

-- 
With best wishes
Dmitry