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

[Marek Vasut]

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.

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).

> 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 ?

[...]