linux-kernel - Re: [PATCH v11 1/4] drm/msm/dp: do not initialize phy until plugin interrupt received

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Date:   Thu, 13 Jan 2022 15:13:07 -0800
From:   Stephen Boyd <swboyd@...omium.org>
To:     Kuogee Hsieh <quic_khsieh@...cinc.com>, agross@...nel.org,
        airlied@...ux.ie, bjorn.andersson@...aro.org, daniel@...ll.ch,
        dmitry.baryshkov@...aro.org, dri-devel@...ts.freedesktop.org,
        robdclark@...il.com, sean@...rly.run, vkoul@...nel.org
Cc:     quic_abhinavk@...cinc.com, aravindh@...eaurora.org,
        quic_sbillaka@...cinc.com, freedreno@...ts.freedesktop.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v11 1/4] drm/msm/dp: do not initialize phy until plugin
 interrupt received

Quoting Kuogee Hsieh (2022-01-13 14:14:27)
>
> On 1/13/2022 1:52 PM, Stephen Boyd wrote:
> > Quoting Kuogee Hsieh (2022-01-13 12:44:16)
> >> On 1/13/2022 11:47 AM, Stephen Boyd wrote:
> >>> Quoting Kuogee Hsieh (2022-01-13 09:51:42)
> >>>> On 1/12/2022 8:13 PM, Stephen Boyd wrote:
> >>>>>>>> -       if (dp->usbpd->orientation == ORIENTATION_CC2)
> >>>>>>>> -               flip = true;
> >>>>>>>> +       dp_power_init(dp->power, false);
> >>>>>>>> +       dp_ctrl_reset_irq_ctrl(dp->ctrl, true);
> >>>>>>>> +
> >>>>>>>> +       /*
> >>>>>>>> +        * eDP is the embedded primary display and has its own phy
> >>>>>>>> +        * initialize phy immediately
> >>>>>>> Question still stands why we can't wait for hpd high from the eDP panel.
> >>>>>>> Also, I think "has its own phy" means that it's not part of a combo
> >>>>>>> USB+DP phy? Can you please clarify?
> >> Correct, eDP has its dedicated phy which is not part of combo phy.
> > Why does that mean we can't wait for hpd high from the eDP panel?
>
> Sorry, missed this one.
>
> Yes, it can wait for hpd high.
>
> Since it always presented, I just think it is better to show display
> sooner not later until hdp high.
>
> you like it to wait until hpd high?

Yes. The less special cases the easier it is to read and modify later. I
also worry that someone will decide to connect a DP connector to the eDP
pins and then not always drive HPD high. In that case this code would
need to change so it seems better to follow one flow instead of two.