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

[Marek Vasut <marex@denx.de>]

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/e845274b0f22ba3b24813ffd6bb3cb88ab4b67e4
>>> and
>>> https://github.com/aford173/linux/commit/3f90057eb608f96d106029ef639813475241936f
>>>
>>> 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.