Re: [PATCH] arm64: dts: imx8mp: Add TC9595 bridge on DH electronics i.MX8M Plus DHCOM

[Marek Vasut <marex@denx.de>]

On 5/24/23 08:49, Alexander Stein wrote:
> Hi Marek,

Hi,

> Am Dienstag, 23. Mai 2023, 15:10:05 CEST schrieb Marek Vasut:
>> On 5/23/23 13:17, Alexander Stein wrote:
>>> Hello Marek,
>>
>> Hi,
>>
>>> Am Montag, 15. Mai 2023, 18:24:24 CEST schrieb Marek Vasut:
>>>> Add TC9595 DSI-to-DPI and DSI-to-(e)DP bridge to
>>>> DH electronics i.MX8M Plus DHCOM SoM . The bridge
>>>> is populated on the SoM, but disabled by default
>>>> unless used for display output.
>>>>
>>>> Signed-off-by: Marek Vasut <marex@denx.de>
>>>
>>> Were you actually able to access the display? E.g. reading DPCD via AUX
>>> channel?
>>
>> I only tried the full display port (the one with large plug) on the TC
>> evaluation kit, there I could use the aux channel. Are you testing this
>> bridge and running into issues ? Details please ?
> 
> Which SoC is this evaluation kit based on?

There is no SoC attached to it, it's just a breakout board for the 
bridge chip. You can attach it via DSI to whichever SoC you want. So far 
I tried STM32MP15xx and i.MX8MP.

> Yes, I'm trying to test this bridge on imx8mp based board.
> 
> AFAICS I run into a timeout during drm connector .get_modes call, see kernel
> log below.
> 
>> samsung-dsim 32e60000.dsi: [drm:samsung_dsim_host_attach [samsung_dsim]]
> Attached tc358767 device
>> tc358767 1-000f: failed to read DPCD: -110
>> tc358767 1-000f: failed to read display props: -110

How are you supplying clock to the TC358767 (or newer) ?
Do you supply clock from DSI or from Xtal ?
If DSI and if possible, switch to Xtal and see whether that helps.
Also check the Xtal frequency and make sure you define that correctly in DT.

> Looking at the AUX_CH+/- signals, I can see the native aux request and the
> (presumable) correct answer (DP_DPCD_REV register) from the display. But for
> some reason the bridge runs into a aux timeout.
> I can see in the DP0_AUXSTATUS register the bus gets busy (0x1) after starting
> transfer. But after the tc_aux_wait_busy() call DP0_AUXSTATUS his indicating a
> timeout and sync error (0x310002).
> When changing the "Aux Bit Period Calculator Threshold" to 5 (register
> AUXCFG1), the sync error is gone, but the timeout still happens.
> 
> The frequency used from the display is ~1MHz, which should be okay. So on the
> electrical side all seems okay, but the native aux transfer don't work.

I recall DPCD read timeouts, but those were usually triggered by either 
bad clock or wiring problems (the devkit wiring I used was horrible at 
the beginning) from what I can recall.