linux-kernel - RE: [RFC PATCH 2/2] drm/msm/dp: enable pm

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Message-ID: <511d7b597b68441d8596dcb51ff18a5d@quicinc.com>
Date:   Wed, 1 Mar 2023 08:19:14 +0000
From:   "Sankeerth Billakanti (QUIC)" <quic_sbillaka@...cinc.com>
To:     "Bjorn Andersson (QUIC)" <quic_bjorande@...cinc.com>
CC:     "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
        "freedreno@...ts.freedesktop.org" <freedreno@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "robdclark@...il.com" <robdclark@...il.com>,
        "seanpaul@...omium.org" <seanpaul@...omium.org>,
        "swboyd@...omium.org" <swboyd@...omium.org>,
        "Kalyan Thota (QUIC)" <quic_kalyant@...cinc.com>,
        "Abhinav Kumar (QUIC)" <quic_abhinavk@...cinc.com>,
        "dianders@...omium.org" <dianders@...omium.org>,
        "Kuogee Hsieh (QUIC)" <quic_khsieh@...cinc.com>,
        "sean@...rly.run" <sean@...rly.run>,
        "airlied@...ux.ie" <airlied@...ux.ie>,
        "daniel@...ll.ch" <daniel@...ll.ch>,
        "dmitry.baryshkov@...aro.org" <dmitry.baryshkov@...aro.org>,
        "Vishnuvardhan Prodduturi (QUIC)" <quic_vproddut@...cinc.com>
Subject: RE: [RFC PATCH 2/2] drm/msm/dp: enable pm_runtime support for dp
 driver

>> diff --git a/drivers/gpu/drm/msm/dp/dp_aux.c
>> b/drivers/gpu/drm/msm/dp/dp_aux.c
>[..]
>> +static int dp_runtime_resume(struct device *dev) {
>> +	struct platform_device *pdev = to_platform_device(dev);
>> +	struct msm_dp *dp_display = platform_get_drvdata(pdev);
>> +	struct dp_display_private *dp;
>> +
>> +	dp = container_of(dp_display, struct dp_display_private, dp_display);
>> +	dp_display_host_init(dp);
>> +
>> +	if (dp->dp_display.is_edp) {
>> +		dp_display_host_phy_init(dp);
>> +	} else {
>> +		dp_catalog_hpd_config_intr(dp->catalog,
>> +				DP_DP_HPD_PLUG_INT_MASK |
>> +				DP_DP_HPD_UNPLUG_INT_MASK,
>> +				true);
>
>I believe this is backwards.
>
>Only in the event that there's no "downstream" HPD handler should we use
>the internal HPD. This is signalled by the DRM framework by a call to
>dp_bridge_hpd_enable(). So we should use that to enable/disable the
>internal HPD handler.
>
>When this happens, we have a reason for keeping power on; i.e. call
>pm_runtime_get(). Once we have power/clocking, we'd call
>dp_catalog_hpd_config_intr(), from dp_bridge_hpd_enable().
>
>
>In the case that the internal HPD handling is not use,
>dp_bridge_hpd_enable() will not be called, instead once the downstream hpd
>handler switches state dp_bridge_hpd_notify() will be invoked.
>
>In this case, we need the DP controller to be powered/clocked between
>connector_status_connected and connector_status_disconnected.
>
>
>I believe this should allow the DP controller(s) to stay powered down in the
>case where we have external HPD handling (e.g. USB Type-C or gpio-based
>dp-connector).
>
>Regards,
>Bjorn

I agree with the approach. I am moving my dev to msm-next. Will make the changes according to the HPD handling and repost

Thank you,
Sankeerth