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

[Adam Ford]

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.

adam