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

[Marek Vasut]

On 12/18/22 05:23, Adam Ford wrote:
> On Sat, Dec 17, 2022 at 5:56 PM Marek Vasut <marex at 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/