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

[Marek Vasut]

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.