Re: [PATCH][RESEND] drm/bridge: ti-sn65dsi83: Check link status register after enabling the bridge

[Dave Stevenson <dave.stevenson@raspberrypi.com>]

Hi Laurent

On Tue, 5 Apr 2022 at 12:42, Laurent Pinchart
<laurent.pinchart@ideasonboard.com> wrote:
>
> Hi Marek,
>
> Thank you for the patch.
>
> On Sun, Feb 13, 2022 at 03:26:48AM +0100, Marek Vasut wrote:
> > In rare cases, the bridge may not start up correctly, which usually
> > leads to no display output. In case this happens, warn about it in
> > the kernel log.
>
> Do you know what this is caused by ? It's a bit annoying to add a 10+ms
> delay at start time just to be notified of rare cases.

The datasheet [1] section 7.4.2 Initialization Sequence states in step 2
"After power is applied and stable, the DSI CLK lanes MUST be in HS
state and the DSI data lanes MUST be driven
to LP11 state"
Data lanes shouldn't go to HS until step 8 after the DSI83 has been configured.

Configuration from the driver is being done from atomic_enable,
therefore the data lanes are likely in HS mode and sending video, not
LP11.

Deviate from the specified initialisation sequence at your peril!

The SN65DSI8[3|4|5] is one of the DSI devices that I'd been looking at
with the DSI ordering patches [2] so that we could initialise it in
the way specified in the datasheet. I've had no responses to v2 of
those patches though.

  Dave

[1] https://www.ti.com/lit/ds/symlink/sn65dsi83.pdf
[2] https://patchwork.freedesktop.org/series/100252/#rev2

> > Signed-off-by: Marek Vasut <marex@denx.de>
> > Cc: Jagan Teki <jagan@amarulasolutions.com>
> > Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> > Cc: Linus Walleij <linus.walleij@linaro.org>
> > Cc: Robert Foss <robert.foss@linaro.org>
> > Cc: Sam Ravnborg <sam@ravnborg.org>
> > Cc: dri-devel@lists.freedesktop.org
> > ---
> >  drivers/gpu/drm/bridge/ti-sn65dsi83.c | 5 +++++
> >  1 file changed, 5 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi83.c b/drivers/gpu/drm/bridge/ti-sn65dsi83.c
> > index 19daaddd29a41..1d7c154ea1d79 100644
> > --- a/drivers/gpu/drm/bridge/ti-sn65dsi83.c
> > +++ b/drivers/gpu/drm/bridge/ti-sn65dsi83.c
> > @@ -488,6 +488,11 @@ static void sn65dsi83_atomic_enable(struct drm_bridge *bridge,
> >       /* Clear all errors that got asserted during initialization. */
> >       regmap_read(ctx->regmap, REG_IRQ_STAT, &pval);
> >       regmap_write(ctx->regmap, REG_IRQ_STAT, pval);
> > +
> > +     usleep_range(10000, 12000);
> > +     regmap_read(ctx->regmap, REG_IRQ_STAT, &pval);
> > +     if (pval)
> > +             dev_err(ctx->dev, "Unexpected link status 0x%02x\n", pval);
> >  }
> >
> >  static void sn65dsi83_atomic_disable(struct drm_bridge *bridge,
>
> --
> Regards,
>
> Laurent Pinchart