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

[Dmitry Baryshkov]

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?

> 
>> 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 ?
>>
>> @Jagan, Andrezej So you have any documentation on what 
>> DSIM_xxx_DISABLE_MODE does ?
> 
> See above, i.MX8M M/N/P uses the samsung-dsim block .
> 
>> @Dmitry, so you have access to the lt9611 datasheet to know what's 
>> needed here ?
> 
> [...]

-- 
With best wishes
Dmitry