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

[Jagan Teki]

On Thu, Jul 13, 2023 at 11:39 PM Abhinav Kumar
<quic_abhinavk at quicinc.com> wrote:
>
>
>
> On 7/12/2023 10:41 AM, Marek Vasut wrote:
> > On 7/9/23 03:03, Abhinav Kumar wrote:
> >>
> >>
> >> On 7/7/2023 1:47 AM, 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 think there's a mismatch, where on one side this flags sets the
> >>> link in LP-11 while
> >>> in HSA/HFP/HPB while on the other it completely removes those
> >>> blanking packets.
> >>>
> >>> The name MIPI_DSI_MODE_VIDEO_NO_HBP suggests removal of HPB, not
> >>> LP-11 while HPB.
> >>> the registers used in both controllers are different:
> >>> - samsung-dsim: DSIM_HBP_DISABLE_MODE
> >>> - msm dsi: DSI_VID_CFG0_HBP_POWER_STOP
> >>>
> >>> The first one suggest removing the packet, while the second one
> >>> suggests powering
> >>> off the line while in the blanking packet period.
> >>>
> >>> @Abhinav, can you comment on that ?
> >>>
> >>
> >> I dont get what it means by completely removes blanking packets in DSIM.
> >
> > MIPI_DSI_MODE_VIDEO_NO_HFP means the HBP period is just skipped by DSIM.
> >
> > Maybe there is a need for new set of flags which differentiate between
> > HBP skipped (i.e. NO HBP) and HBP LP11 ?
> >
>
> No, the section of the MIPI DSI spec I posted below clearly states there
> are two options:
>
> 1) send blanking packets during those periods
> 2) transition to LP11 during those periods
>
> There is no 3rd option in the spec of not doing both like what you are
> suggesting. So DSIM should also be only transitioning to LP11 during
> those periods if its not sending the blanking packets with those flags set.
>
> So, there is no need for any new set of flags to differentiate.
>
> The flags and their interpretation is correct in MSM driver. I cannot
> comment on what exactly DSIM does with those flags.

As many of them know all these flags are generic across controllers
I'm trying to add these flag notations from DSIM controller and how
they handle the driver.

HBP/HFP/HSA mode bits in i.MX8M Mini/Nano/Plus Processor Reference
Manuals specify a naming conversion as 'disable mode bit' due to its
bit definition,  0 = Enable and 1 = Disable.

Example HBP (HbpDisableMode)- Specifies HBP disable mode. If this bit
set, DSI master ignores HBP area in Video mode.
 0 = Enables
 1 = Disables

 if (dsi->mode_flags & MIPI_DSI_MODE_VIDEO_NO_HFP)
           reg |= DSIM_HFP_DISABLE_MODE;
 if (dsi->mode_flags & MIPI_DSI_MODE_VIDEO_NO_HBP)
           reg |= DSIM_HBP_DISABLE_MODE;
 if (dsi->mode_flags & MIPI_DSI_MODE_VIDEO_NO_HSA)
            reg |= DSIM_HSA_DISABLE_MODE;

I'm hoping this will give some information.

Thanks,
Jagan.