[PATCH v3 7/7] drm/bridge: ti-sn65dsi86: Add mystery delay to enable()
Sean Paul
sean at poorly.run
Mon Aug 27 15:28:00 UTC 2018
On Mon, Aug 27, 2018 at 07:40:05AM +0530, spanda at codeaurora.org wrote:
> On 2018-08-14 03:00, Sean Paul wrote:
> > From: Sean Paul <seanpaul at chromium.org>
> >
> > This patch adds a 70ms mystery delay to the bridge driver in enable.
> > By experimentation, it seems like it can go anywhere up until we
> > initiate semi-auto link training. If we don't have the delay, link
> > training fails.
> >
> > I tried to root cause this as best I could, but neither the datasheet
> > for the panel nor the bridge mention a delay of this magnitude in their
> > timing requirements. So for now, add the mystery delay until someone
> > figures out a better fix.
> >
> > Changes in v3:
> > - Added to the set
> >
> > Cc: Sandeep Panda <spanda at codeaurora.org>
> > Signed-off-by: Sean Paul <seanpaul at chromium.org>
> > ---
> > drivers/gpu/drm/bridge/ti-sn65dsi86.c | 12 ++++++++++++
> > 1 file changed, 12 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> > b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> > index d3e27e52ea759..f8a931cf3665e 100644
> > --- a/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> > +++ b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> > @@ -458,6 +458,18 @@ static void ti_sn_bridge_enable(struct drm_bridge
> > *bridge)
> > unsigned int val;
> > int ret;
> >
> > + /*
> > + * FIXME:
> > + * This 70ms was found necessary by experimentation. If it's not
> > + * present, link training fails. It seems like it can go anywhere from
> > + * pre_enable() up to semi-auto link training initiation below.
> > + *
> > + * Neither the datasheet for the bridge nor the panel tested mention a
> > + * delay of this magnitude in the timing requirements. So for now, add
> > + * the mystery delay until someone figures out a better fix.
> > + */
> > + msleep(70);
> > +
> > /* DSI_A lane config */
> > val = CHA_DSI_LANES(4 - pdata->dsi->lanes);
> > regmap_update_bits(pdata->regmap, SN_DSI_LANES_REG,
>
> Reviewed-by: Sandeep Panda <spanda at codeaurora.org>
Pushed to -misc-next, thanks for your reviews.
Sean
--
Sean Paul, Software Engineer, Google / Chromium OS
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