linux-kernel - Re: [PATCH v3] drm/msm/dsi: only powerup at modeset time if "early

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Message-ID: <CAD=FV=UhTuhOOjG15S=bXQBq1UAskr2s5fubsD4xvnp589-8_Q@mail.gmail.com>
Date:   Thu, 12 May 2022 15:01:58 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc:     Rob Clark <robdclark@...il.com>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Dave Stevenson <dave.stevenson@...pberrypi.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>, Sean Paul <sean@...rly.run>,
        Stephen Boyd <swboyd@...omium.org>,
        Vinod Koul <vkoul@...nel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        freedreno <freedreno@...ts.freedesktop.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] drm/msm/dsi: only powerup at modeset time if
 "early_poweron" modparam

Hi,

On Thu, May 12, 2022 at 1:59 PM Dmitry Baryshkov
<dmitry.baryshkov@...aro.org> wrote:
>
> On 12/05/2022 23:52, Douglas Anderson wrote:
> > Commit 7d8e9a90509f ("drm/msm/dsi: move DSI host powerup to modeset
> > time") caused sc7180 Chromebooks that use the parade-ps8640 bridge
> > chip to fail to turn the display back on after it turns off.
> >
> > Unfortunately, it doesn't look easy to fix the parade-ps8640 driver to
> > handle the new power sequence. The Linux driver has almost nothing in
> > it and most of the logic for this bridge chip is in black-box firmware
> > that the bridge chip uses.
> >
> > Also unfortunately, reverting the patch will break "tc358762".
> >
> > The long term solution here is probably Dave Stevenson's series [1]
> > that would give more flexibility. However, that is likely not a quick
> > fix.
> >
> > For the short term, let's introduce a module parameter that selects
> > between the two behaviors. This is a short term hack but at least can
> > keep both users working. We'll default the value of the module
> > parameter to the old behavior. Given that the old behavior has existed
> > for longer it's probably a safer default.
> >
> > [1] https://lore.kernel.org/r/cover.1646406653.git.dave.stevenson@raspberrypi.com
> >
> > Fixes: 7d8e9a90509f ("drm/msm/dsi: move DSI host powerup to modeset time")
> > Suggested-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
> > Signed-off-by: Douglas Anderson <dianders@...omium.org>
>
> Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
>
> Two minor issues below.

I only saw one, so hopefully I didn't miss another request. ;-)


> > ---
> >
> > Changes in v3:
> > - No longer a revert; now a module parameter.
> >
> > Changes in v2:
> > - Remove the mud from my face.
> >
> >   drivers/gpu/drm/msm/dsi/dsi_manager.c | 10 +++++++++-
> >   1 file changed, 9 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/msm/dsi/dsi_manager.c b/drivers/gpu/drm/msm/dsi/dsi_manager.c
> > index 50b987658b1f..2bf4123ef5df 100644
> > --- a/drivers/gpu/drm/msm/dsi/dsi_manager.c
> > +++ b/drivers/gpu/drm/msm/dsi/dsi_manager.c
> > @@ -34,6 +34,10 @@ static struct msm_dsi_manager msm_dsim_glb;
> >   #define IS_SYNC_NEEDED()    (msm_dsim_glb.is_sync_needed)
> >   #define IS_MASTER_DSI_LINK(id)      (msm_dsim_glb.master_dsi_link_id == id)
> >
> > +bool early_poweron;
> > +MODULE_PARM_DESC(early_poweron, "Power DSI controller early");
> > +module_param(early_poweron, bool, 0600);
>
> Nit: dsi_early_poweron (to be clear that it related to DSI only).
>
> I thought about suggesting 'dsi_no_early_poweron' instead to catch
> possible issues with other bridges. But... I think with Dave's series
> will have to enable bridges one by one, so it doesn't make real sense.

I made the change you requested and was about to send out a v4 when
offline Rob pointed out a better way that seems to work. I can use the
`compatible` of the next bridge. I've sent out v4 as per Rob's
suggestion:

https://lore.kernel.org/r/20220512145954.v4.1.Ia196e35ad985059e77b038a41662faae9e26f411@changeid

-Doug