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

[Neil Armstrong]

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 ?

Neil

> 
> Regards,
> Amit Pundir
> [1] https://people.linaro.org/~amit.pundir/db845c-userdebug/v6.5-broken-display/PXL_20230704_150156326.jpg
> 
>>
>> --
>> With best wishes
>> Dmitry