[PATCH 2/2] drm/bridge: lt9611: Do not generate HFP/HBP/HSA and EOT packet

[Dmitry Baryshkov]

On Sat, 8 Jul 2023 at 22:39, Marek Vasut <marex at denx.de> wrote:
>
> On 7/8/23 17:53, Dmitry Baryshkov wrote:
> > On 08/07/2023 18:40, Marek Vasut wrote:
> >> On 7/7/23 10:47, Neil Armstrong wrote:
> >>> On 07/07/2023 09:18, Neil Armstrong wrote:
> >>>> Hi,
> >>>>
> >>>> On 06/07/2023 11:20, Amit Pundir wrote:
> >>>>> On Wed, 5 Jul 2023 at 11:09, Dmitry Baryshkov
> >>>>> <dmitry.baryshkov at linaro.org> wrote:
> >>>>>>
> >>>>>> [Adding freedreno@ to cc list]
> >>>>>>
> >>>>>> On Wed, 5 Jul 2023 at 08:31, Jagan Teki
> >>>>>> <jagan at amarulasolutions.com> wrote:
> >>>>>>>
> >>>>>>> Hi Amit,
> >>>>>>>
> >>>>>>> On Wed, Jul 5, 2023 at 10:15 AM Amit Pundir
> >>>>>>> <amit.pundir at linaro.org> wrote:
> >>>>>>>>
> >>>>>>>> Hi Marek,
> >>>>>>>>
> >>>>>>>> On Wed, 5 Jul 2023 at 01:48, Marek Vasut <marex at denx.de> wrote:
> >>>>>>>>>
> >>>>>>>>> Do not generate the HS front and back porch gaps, the HSA gap and
> >>>>>>>>> EOT packet, as these packets are not required. This makes the
> >>>>>>>>> bridge
> >>>>>>>>> work with Samsung DSIM on i.MX8MM and i.MX8MP.
> >>>>>>>>
> >>>>>>>> This patch broke display on Dragonboard 845c (SDM845) devboard
> >>>>>>>> running
> >>>>>>>> AOSP. This is what I see
> >>>>>>>> https://people.linaro.org/~amit.pundir/db845c-userdebug/v6.5-broken-display/PXL_20230704_150156326.jpg.
> >>>>>>>> Reverting this patch fixes this regression for me.
> >>>>>>>
> >>>>>>> Might be msm dsi host require proper handling on these updated
> >>>>>>> mode_flags? did they?
> >>>>>>
> >>>>>> The msm DSI host supports those flags. Also, I'd like to point out
> >>>>>> that the patch didn't change the rest of the driver code. So even if
> >>>>>> drm/msm ignored some of the flags, it should not have caused the
> >>>>>> issue. Most likely the issue is on the lt9611 side. I's suspect that
> >>>>>> additional programming is required to make it work with these flags.
> >>>>>
> >>>>> I spent some time today on smoke testing these flags (individually and
> >>>>> in limited combination) on DB845c, to narrow down this breakage to one
> >>>>> or more flag(s) triggering it. Here are my observations in limited
> >>>>> testing done so far.
> >>>>>
> >>>>> There is no regression with MIPI_DSI_MODE_NO_EOT_PACKET when enabled
> >>>>> alone and system boots to UI as usual.
> >>>>>
> >>>>> MIPI_DSI_MODE_VIDEO_NO_HFP always trigger the broken display as in the
> >>>>> screenshot[1] shared earlier as well.
> >>>>>
> >>>>> Adding either of MIPI_DSI_MODE_VIDEO_NO_HSA and
> >>>>> MIPI_DSI_MODE_VIDEO_NO_HBP always result in no display, unless paired
> >>>>> with MIPI_DSI_MODE_VIDEO_NO_HFP and in that case we get the broken
> >>>>> display as reported.
> >>>>>
> >>>>> In short other than MIPI_DSI_MODE_NO_EOT_PACKET flag, all other flags
> >>>>> added in this commit break the display on DB845c one way or another.
> >>>>
> >>>> I think the investigation would be to understand why samsung-dsim
> >>>> requires
> >>>> such flags and/or what are the difference in behavior between MSM
> >>>> DSI and samsung DSIM
> >>>> for those flags ?
> >>>>
> >>>> If someone has access to the lt9611 datasheet, so it requires
> >>>> HSA/HFP/HBP to be
> >>>> skipped ? and does MSM DSI and samsung DSIM skip them in the same way ?
> >>
> >> I don't have the LT9611 datasheet, no.
> >
> > I also don't have an lt9611 datasheet, unfortunately. I was using the
> > existing third-party drivers as a source.
> >
> >>
> >> The MX8M DSI (samsung-dsim) skips the HSA/HFP/HBP completely (see
> >> i.MX8MP RM 13.6.2.7.2 RGB Interface , there is infographics on the
> >> following pages).
> >
> > Do you know, why did you have to disable HPB/HSA/HFP on your platform?
> > What was the result otherwise?
>
> No image on the HDMI monitor at all. This flags change has fixed the
> problem for multiple other bridges too btw, not just the LT9611, but
> also TI SN65DSI83 and ICN6211. The flags were likely not set in all
> those bridge drivers because no DSI host implemented them so far.

MSM DSI host have had those implemented for ages, but we never needed
them AFAIR.

-- 
With best wishes
Dmitry