Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
In-Reply-To: <1650618666-15342-4-git-send-email-quic_sbillaka@quicinc.com>
References: <1650618666-15342-1-git-send-email-quic_sbillaka@quicinc.com> <1650618666-15342-4-git-send-email-quic_sbillaka@quicinc.com>
From:   Stephen Boyd <swboyd@chromium.org>
User-Agent: alot/0.10
Date:   Fri, 22 Apr 2022 18:38:46 -0700
Message-ID: <CAE-0n520s1XdUO5k2xxX16AsJc8pCjV8yXeR-0f5BC7A5+f-Vw@mail.gmail.com>
Subject: Re: [PATCH v9 3/4] drm/msm/dp: wait for hpd high before aux transaction
To:     Sankeerth Billakanti <quic_sbillaka@quicinc.com>,
        devicetree@vger.kernel.org, dri-devel@lists.freedesktop.org,
        freedreno@lists.freedesktop.org, linux-arm-msm@vger.kernel.org,
        linux-kernel@vger.kernel.org
Cc:     robdclark@gmail.com, seanpaul@chromium.org,
        quic_kalyant@quicinc.com, quic_abhinavk@quicinc.com,
        dianders@chromium.org, quic_khsieh@quicinc.com,
        bjorn.andersson@linaro.org, sean@poorly.run, airlied@linux.ie,
        daniel@ffwll.ch, dmitry.baryshkov@linaro.org,
        quic_vproddut@quicinc.com, quic_aravindh@quicinc.com,
        steev@kali.org
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

Quoting Sankeerth Billakanti (2022-04-22 02:11:05)
> The source device should ensure the sink is ready before proceeding to
> read the sink capability or perform any aux transactions. The sink
> will indicate its readiness by asserting the HPD line. The controller
> driver needs to wait for the hpd line to be asserted by the sink before
> it performs any aux transactions.
>
> The eDP sink is assumed to be always connected. It needs power from the
> source and its HPD line will be asserted only after the panel is powered
> on. The panel power will be enabled from the panel-edp driver and only
> after that, the hpd line will be asserted.
>
> Whereas for DP, the sink can be hotplugged and unplugged anytime. The hpd
> line gets asserted to indicate the sink is connected and ready. Hence
> there is no need to wait for the hpd line to be asserted for a DP sink.
>
> Signed-off-by: Sankeerth Billakanti <quic_sbillaka@quicinc.com>
> Reviewed-by: Douglas Anderson <dianders@chromium.org>
> ---

Reviewed-by: Stephen Boyd <swboyd@chromium.org>