linux-kernel - RE: [PATCH v6 5/8] drm/msm/dp: prevent multiple votes for dp resources

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Date:   Fri, 8 Apr 2022 17:12:49 +0000
From:   Sankeerth Billakanti <sbillaka@....qualcomm.com>
To:     "dmitry.baryshkov@...aro.org" <dmitry.baryshkov@...aro.org>,
        Doug Anderson <dianders@...omium.org>,
        "Sankeerth Billakanti (QUIC)" <quic_sbillaka@...cinc.com>
CC:     dri-devel <dri-devel@...ts.freedesktop.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        freedreno <freedreno@...ts.freedesktop.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, Rob Clark <robdclark@...il.com>,
        Sean Paul <seanpaul@...omium.org>,
        Stephen Boyd <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 Paul <sean@...rly.run>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        quic_vproddut <quic_vproddut@...cinc.com>,
        "Aravind Venkateswaran (QUIC)" <quic_aravindh@...cinc.com>
Subject: RE: [PATCH v6 5/8] drm/msm/dp: prevent multiple votes for dp
 resources

> > On Wed, Mar 30, 2022 at 9:04 AM Sankeerth Billakanti
> > <quic_sbillaka@...cinc.com> wrote:
> >>
> >> The aux_bus support with the dp_display driver will enable the dp
> >> resources during msm_dp_modeset_init. The host_init has to return
> >> early if the core is already initialized to prevent putting an
> >> additional vote for the dp controller resources.
> >>
> >> Signed-off-by: Sankeerth Billakanti <quic_sbillaka@...cinc.com>
> >> ---
> >>   drivers/gpu/drm/msm/dp/dp_display.c | 10 ++++++++++
> >>   1 file changed, 10 insertions(+)
> >
> > I'm not a huge fan of this but I'll leave it up to Dmitry. In general
> > it feels like there should be _a_ place that enables these resources.
> > Checks like this make it feel like we just scattershot enabling
> > resources in a bunch of random places instead of coming up with the
> > design for enabling them in the right place.
> 
> I'd prefer to see a check for eDP in dp_display_config_hpd(). Or even better
> to see that this function isn't called for eDP at all.
>

This needs to be called when eDP is not using the aux_bus path. If the eDP panel is
given as a separate panel driver, then the resources need to be enabled here.

If we don't want to support eDP without aux_bus, then we can skip this function.
 
> >
> > In any case, if we do end up landing this patch, it sure feels like it
> > needs to move earlier in the patch series, right? This patch shouldn't
> > hurt even without the other patches in the series but if you apply the
> > earlier patches in the series without this one then you'll have a bug,
> > right? That means this needs to come earlier.
> >
> > -Doug
> 
> 
> --
> With best wishes
> Dmitry

Thank you,
Sankeerth