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

[Adam Ford <aford173@gmail.com>]

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.

adam