Re: [PATCH v10 00/18] drm: Add Samsung MIPI DSIM bridge

[Marek Vasut <marex@denx.de>]

On 1/3/23 11:59, Alexander Stein wrote:
> Hi,
> 
> Am Sonntag, 18. Dezember 2022, 23:28:20 CET schrieb Marek Vasut:
>> On 12/18/22 23:24, Adam Ford wrote:
>>> On Sat, Dec 17, 2022 at 10:33 PM Marek Vasut <marex@denx.de> wrote:
>>>> On 12/18/22 05:23, Adam Ford wrote:
>>>>> On Sat, Dec 17, 2022 at 5:56 PM Marek Vasut <marex@denx.de> wrote:
>>>>>> On 12/16/22 14:25, Alexander Stein wrote:
>>>>>> Hi,
>>>>>>
>>>>>> [...]
>>>>>>
>>>>>>> Oh, nice, thanks for the pointer. When setting
>>>>>>>
>>>>>>>> samsung,burst-clock-frequency = <668250000>;
>>>>>>>
>>>>>>> in imx8mm.dtsi
>>>>>>> I get a non-flickering display using 4 lanes. Although admittedly this
>>>>>>> is just random guessing. I'm not sure which clock exactly has to be
>>>>>>> in the range CHA_DSI_CLK_RANGE is configured to. With 4 lanes
>>>>>>> SN65DSI84 is configured for>>>>>
>>>>>>> 205-210 MHz (0x29), while I get these PLL PMS settings on DSIM:
>>>>>>>> samsung-dsim 32e10000.dsi: PLL freq 668250000, (p 4, m 99, s 0)
>>>>>>>> samsung-dsim 32e10000.dsi: hs_clk = 668250000, byte_clk = 83531250,
>>>>>>>> esc_clk
>>>>>>>
>>>>>>> = 16706250
>>>>>>
>>>>>> If I recall it right, minimum PLL frequency is:
>>>>>>
>>>>>> fPMS=1.2*width*height*bpp*fps=1.2*800*480*24*60=663.5 MHz
>>>>>>
>>>>>> the link frequency is then
>>>>>>
>>>>>> fHS=fPMS/lanes/2=82.9 MHz (on the DDR clock lane)
>>>>>>
>>>>>> So DSI83 should be in the range of 80..85 MHz input clock if I
>>>>>> calculate
>>>>>> this right. Can you check what is the value of mode->clock, the
>>>>>> mipi_dsi_panel_format_to_bpp() return value, ctx->dsi->lanes in dsi83
>>>>>> sm65dsi83_get_dsi_range() ?
>>>>>>
>>>>>>> AFAICS DSIM bridge is configurung hs_clk, byte_clk and esc_clk just
>>>>>>> from DT
>>>>>>> properties, while SN65DSI84 is using display mode and number of lanes.
>>>>>>>
>>>>>>> Is it expected that the DSIM PLL frequencies are set in DT for a
>>>>>>> specific
>>>>>>> bridge/display setup?
>>>>>>
>>>>>> No, there should be negotiation between the host and bridge/panel, I
>>>>>> tried to propose two variants, but they were all rejected.
>>>>>
>>>>> For one of Jagan's previous revisions, I added some code to let the
>>>>> PHY auto adjust the frequencies instead of being fixed.  NXP had this
>>>>> in their downstream kernel, but with this patch and another, I was
>>>>> able to set a variety of pixel clocks from my HDMI monitor and my
>>>>> DSI83. I haven't had time to re-base my work on Jagan's latest work,
>>>>> but you can link to the patch I did for the older stuff here:
>>>>>
>>>>> https://github.com/aford173/linux/commit/e845274b0f22ba3b24813ffd6bb3cb8
>>>>> 8ab4b67e4 and
>>>>> https://github.com/aford173/linux/commit/3f90057eb608f96d106029ef6398134
>>>>> 75241936f
>>>>>
>>>>> I've been traveling a lot lately, so I haven't had time to evaluate
>>>>> his series, but I hope to get something like those re-based once the
>>>>> DSI stuff has been accepted.
>>>>
>>>> I have these two attempts, both rejected:
>>>>
>>>> https://patchwork.freedesktop.org/patch/475207/
>>>> https://patchwork.freedesktop.org/patch/496049/
>>>
>>> I have some patches re-based to Jagan's latest branch.  It doesn't
>>> impact any drivers other than the new samsung-dsim driver, and it
>>> doesn't touch any of the drm helper functions either.  It adjusts hs
>>> clock based on the connected device.  I am not sure what the impact
>>> will have on the attached Exynos devices, so I am expecting some
>>> iterations.  Right now it's working with my DSI83 chip, but I need to
>>> get it working with my adv7535 part as well.  On the older branch, I
>>> was able to sync the ad7535 with a variety of resolutions using
>>> different pixel clock rates.
>>>
>>> Once I get it working again with my adv7535 and cleaned up, I'll
>>> submit the patches to the drm group, and I'll CC you, Jagan and Marek
>>> Szyprowski with a reference to Jagan's series so people wanting to try
>>> it can apply it to his branch.
>>
>> The negotiation has to happen between the host and the bridge/panel,
>> otherwise you won't be able to support bridge/panel devices which
>> require specific clock rate on the DSI. Only the bridge/panel driver
>> knows about such requirement.
> 
> AFAICS using Adam's patch the dynamic DPHY config is done in atomic_pre_enable
> callback. So at this point the negotiation has to be finished already.
> Wouldn't it be possible to setup 'dsi->format' within a atomic_check for
> samsung_dsim? But I don't know how you would get the expected clock frequency
> from the downward bridge.

Maybe Maxime can comment on this ?