linux-kernel - Re: [PATCH v6 8/8] drm/msm/dp: Handle eDP mode

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Date:   Thu, 31 Mar 2022 16:24:07 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     "Sankeerth Billakanti (QUIC)" <quic_sbillaka@...cinc.com>
Cc:     "dmitry.baryshkov@...aro.org" <dmitry.baryshkov@...aro.org>,
        "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>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "robdclark@...il.com" <robdclark@...il.com>,
        "seanpaul@...omium.org" <seanpaul@...omium.org>,
        "swboyd@...omium.org" <swboyd@...omium.org>,
        quic_kalyant <quic_kalyant@...cinc.com>,
        "Abhinav Kumar (QUIC)" <quic_abhinavk@...cinc.com>,
        "Kuogee Hsieh (QUIC)" <quic_khsieh@...cinc.com>,
        "bjorn.andersson@...aro.org" <bjorn.andersson@...aro.org>,
        "sean@...rly.run" <sean@...rly.run>,
        "airlied@...ux.ie" <airlied@...ux.ie>,
        "daniel@...ll.ch" <daniel@...ll.ch>,
        quic_vproddut <quic_vproddut@...cinc.com>,
        "Aravind Venkateswaran (QUIC)" <quic_aravindh@...cinc.com>
Subject: Re: [PATCH v6 8/8] drm/msm/dp: Handle eDP mode_valid differently from dp

Hi,

On Wed, Mar 30, 2022 at 11:02 PM Sankeerth Billakanti (QUIC)
<quic_sbillaka@...cinc.com> wrote:
>
> Hi Dmitry,
>
> > On Wed, 30 Mar 2022 at 19:04, Sankeerth Billakanti
> > <quic_sbillaka@...cinc.com> wrote:
> > >
> > > The panel-edp driver modes needs to be validated differently from DP
> > > because the link capabilities are not available for EDP by that time.
> > >
> > > Signed-off-by: Sankeerth Billakanti <quic_sbillaka@...cinc.com>
> >
> > This should not be necessary after
> > https://patchwork.freedesktop.org/patch/479261/?series=101682&rev=1.
> > Could you please check?
> >
>
> The check for DP_MAX_PIXEL_CLK_KHZ is not necessary anymore but we need
> to return early for eDP because unlike DP, eDP context will not have the information
> about the number of lanes and link clock.
>
> So, I will modify the patch to return after the DP_MAX_PIXEL_CLK_KHZ check if is_eDP is set.

I haven't walked through all the relevant code but something you said
above sounds strange. You say that for eDP we don't have info about
the number of lanes? We _should_.

It's certainly possible to have a panel that supports _either_ 1 or 2
lanes but then only physically connect 1 lane to it. ...or you could
have a panel that supports 2 or 4 lanes and you only connect 1 lane.
See, for instance, ti_sn_bridge_parse_lanes. There we assume 4 lanes
but if a "data-lanes" property is present then we can use that to know
that fewer lanes are physically connected.

It's also possible to connect more lanes to a panel than it supports.
You could connect 2 lanes to it but then it only supports 1. This case
needs to be handled as well...


-Doug