On Tue, Aug 14, 2018 at 10:00:33AM -0400, Sean Paul wrote: > On Tue, Aug 14, 2018 at 04:59:31PM +0530, spanda@xxxxxxxxxxxxxx wrote: > > On 2018-08-14 03:00, Sean Paul wrote: > > > From: Sean Paul <seanpaul@xxxxxxxxxxxx> > > > > > > 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@xxxxxxxxxxxxxx> > > > Signed-off-by: Sean Paul <seanpaul@xxxxxxxxxxxx> > > > --- > > > 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. > > > + */ > > > > Is this newly found issue? Specific to any board config? > > It's specific to cheza. Well, I suppose I shouldn't say that since I've not tried the bridge on another board. I should say, it reproduces on cheza. Sean > This was found with swboyd changed the panel regulator > from always-on/boot-on to toggle. > > I've pushed the tag "mtp-testing-0813" to dpu-staging so you can play around > with it. Without this delay, link training fails. > > Sean > > > > > > + msleep(70); > > > + > > > /* DSI_A lane config */ > > > val = CHA_DSI_LANES(4 - pdata->dsi->lanes); > > > regmap_update_bits(pdata->regmap, SN_DSI_LANES_REG, > > -- > Sean Paul, Software Engineer, Google / Chromium OS -- Sean Paul, Software Engineer, Google / Chromium OS _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
