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 14:14:27 -0800
From:   Kuogee Hsieh <quic_khsieh@...cinc.com>
To:     Stephen Boyd <swboyd@...omium.org>, <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


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?

>>>>>>>> +        */
>>>>>>>> +       if (dp->dp_display.connector_type == DRM_MODE_CONNECTOR_eDP)
>>>>>>>> +               dp_display_host_phy_init(dp);
>>>>>>>>
>>>>>>>> -       dp_power_init(dp->power, flip);
>>>>>>>> -       dp_ctrl_host_init(dp->ctrl, flip, reset);
>>>>>>>>             dp_aux_init(dp->aux);
>>>>>>>>             dp->core_initialized = true;
>>>>>>>>      }
>>>>>>>> @@ -1306,20 +1330,23 @@ static int dp_pm_resume(struct device *dev)
>>>>>>>>             dp->hpd_state = ST_DISCONNECTED;
>>>>>>>>
>>>>>>>>             /* turn on dp ctrl/phy */
>>>>>>>> -       dp_display_host_init(dp, true);
>>>>>>>> +       dp_display_host_init(dp);
>>>>>>>>
>>>>>>>>             dp_catalog_ctrl_hpd_config(dp->catalog);
>>>>>>>>
>>>>>>>> -       /*
>>>>>>>> -        * set sink to normal operation mode -- D0
>>>>>>>> -        * before dpcd read
>>>>>>>> -        */
>>>>>>>> -       dp_link_psm_config(dp->link, &dp->panel->link_info, false);
>>>>>>>>
>>>>>>>>             if (dp_catalog_link_is_connected(dp->catalog)) {
>>>>>>>> +               /*
>>>>>>>> +                * set sink to normal operation mode -- D0
>>>>>>>> +                * before dpcd read
>>>>>>>> +                */
>>>>>>>> +               dp_display_host_phy_init(dp);
>>>>>>>> +               dp_link_psm_config(dp->link, &dp->panel->link_info, false);
>>>>>>>>                     sink_count = drm_dp_read_sink_count(dp->aux);
>>>>>>>>                     if (sink_count < 0)
>>>>>>>>                             sink_count = 0;
>>>>>>>> +
>>>>>>>> +               dp_display_host_phy_exit(dp);
>>>>>>> Why is the phy exited on resume when the link is still connected? Is
>>>>>>> this supposed to be done only when the sink_count is 0? And how does
>>>>>>> this interact with eDP where the phy is initialized by the call to
>>>>>>> dp_display_host_init() earlier in this function.
>> At beginning of dp_pm_resume bot core_initialized and phy_initialized
>> should be off.
>>
>> However at the case of dongle still connected to DUT, we have to read
>> dongle dpcd to decided any hdmi connect to dongle (sink_count != 0). in
>> this case, we have to turn on phy to perform dpcd read and  turn off phy
>> after read so the following plugged-in interrupt can be handled correctly.
>>
> That looks like a lot of wasted work. Why can't we turn on the core,
> turn on the phy, check if it's connected, and then turn off the phy if
> it isn't? At the least, please put a comment above this phy_exit() call
> indicating that we'll turn the phy back on while processing a plugged in
> interrupt.