linux-kernel - Re: [RFT PATCH v2 1/3] drm/bridge: tc358762: Set pre_enable_prev

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Date:   Mon, 27 Feb 2023 16:26:47 -0800
From:   Doug Anderson <dianders@...omium.org>
To:     Dave Stevenson <dave.stevenson@...pberrypi.com>
Cc:     dri-devel@...ts.freedesktop.org, Rob Clark <robdclark@...il.com>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        freedreno@...ts.freedesktop.org,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Jonas Karlman <jonas@...boo.se>, linux-arm-msm@...r.kernel.org,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Robert Foss <robert.foss@...aro.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Vinod Koul <vkoul@...nel.org>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Andrzej Hajda <andrzej.hajda@...el.com>,
        Sean Paul <sean@...rly.run>, linux-kernel@...r.kernel.org
Subject: Re: [RFT PATCH v2 1/3] drm/bridge: tc358762: Set pre_enable_prev_first

Hi,

On Wed, Feb 1, 2023 at 1:51 AM Dave Stevenson
<dave.stevenson@...pberrypi.com> wrote:
>
> On Tue, 31 Jan 2023 at 22:22, Douglas Anderson <dianders@...omium.org> wrote:
> >
> > Set the "pre_enable_prev_first" as provided by commit 4fb912e5e190
> > ("drm/bridge: Introduce pre_enable_prev_first to alter bridge init
> > order"). This should allow us to revert commit ec7981e6c614
> > ("drm/msm/dsi: don't powerup at modeset time for parade-ps8640") and
> > commit 7d8e9a90509f ("drm/msm/dsi: move DSI host powerup to modeset
> > time").
>
> I see no reference in the TC358762 datasheet to requiring the DSI
> interface to be in any particular state.
> However, setting this flag does mean that the DSI host doesn't need to
> power up and down for each host_transfer request from
> tc358762_pre_enable/tc358762_init, so on that basis I'm good with it.
>
> Reviewed-by: Dave Stevenson <dave.stevenson@...pberrypi.com>
>
> > Cc: Dave Stevenson <dave.stevenson@...pberrypi.com>
> > Cc: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
> > Cc: Abhinav Kumar <quic_abhinavk@...cinc.com>
> > Signed-off-by: Douglas Anderson <dianders@...omium.org>
> > ---
> >
> > (no changes since v1)
> >
> >  drivers/gpu/drm/bridge/tc358762.c | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/drivers/gpu/drm/bridge/tc358762.c b/drivers/gpu/drm/bridge/tc358762.c
> > index 0b6a28436885..77f7f7f54757 100644
> > --- a/drivers/gpu/drm/bridge/tc358762.c
> > +++ b/drivers/gpu/drm/bridge/tc358762.c
> > @@ -229,6 +229,7 @@ static int tc358762_probe(struct mipi_dsi_device *dsi)
> >         ctx->bridge.funcs = &tc358762_bridge_funcs;
> >         ctx->bridge.type = DRM_MODE_CONNECTOR_DPI;
> >         ctx->bridge.of_node = dev->of_node;
> > +       ctx->bridge.pre_enable_prev_first = true;
> >
> >         drm_bridge_add(&ctx->bridge);

Abhinav asked what the plan was for landing this [1]. Since this isn't
urgent, I guess the plan is to land patch #1 in drm-misc-next. Then we
sit and wait until it percolates into mainline and, once it does, then
patch #2 and #3 can land.

Since I have Dave's review I can commit this to drm-misc-next myself.
My plan will be to wait until Thursday or Friday of this week (to give
people a bit of time to object) and then land patch #1. Then I'll
snooze things for a while and poke Abhinav and Dmitry to land patch #2
/ #3 when I notice it in mainline. If, at any point, someone comes out
of the woodwork and yells that this is breaking them then, worst case,
we can revert.

[1] https://lore.kernel.org/r/1f204585-88e2-abae-1216-92f739ac9e91@quicinc.com/