Re: [PATCH] drm: lcdif: Use adjusted_mode .clock instead of .crtc_clock

[Isaac Scott <isaac.scott@ideasonboard.com>]

On Thu, 2024-10-10 at 13:31 +0800, Liu Ying wrote:
> On 10/09/2024, Marek Vasut wrote:
> > On 10/8/24 12:07 PM, Isaac Scott wrote:
> > > On Mon, 2024-10-07 at 20:06 +0200, Marek Vasut wrote:
> > > > On 10/7/24 7:01 PM, Isaac Scott wrote:
> > > > > Hi Marek,
> > > > 
> > > > Hi,
> > > > 
> > > > > On Sat, 2024-07-06 at 02:16 +0200, Marek Vasut wrote:
> > > > > > On 6/24/24 11:19 AM, Alexander Stein wrote:
> > > > > > > Am Freitag, 31. Mai 2024, 22:27:21 CEST schrieb Marek
> > > > > > > Vasut:
> > > > > > > > In case an upstream bridge modified the required clock
> > > > > > > > frequency
> > > > > > > > in its .atomic_check callback by setting
> > > > > > > > adjusted_mode.clock
> > > > > > > > ,
> > > > > > > > make sure that clock frequency is generated by the
> > > > > > > > LCDIFv3
> > > > > > > > block.
> > > > > > > > 
> > > > > > > > This is useful e.g. when LCDIFv3 feeds DSIM which feeds
> > > > > > > > TC358767
> > > > > > > > with (e)DP output, where the TC358767 expects precise
> > > > > > > > timing
> > > > > > > > on
> > > > > > > > its input side, the precise timing must be generated by
> > > > > > > > the
> > > > > > > > LCDIF.
> > > > > > > > 
> > > > > > > > Signed-off-by: Marek Vasut <marex@denx.de>
> > > > > > > 
> > > > > > > With the other rc358767 patches in place, this does the
> > > > > > > trick.
> > > > > > > Reviewed-by: Alexander Stein
> > > > > > > <alexander.stein@ew.tq-group.com>
> > > > > > 
> > > > > > I'll pick this up next week if there is no objection.
> > > > > 
> > > > > Unfortunately, this has caused a regression that is present
> > > > > in
> > > > > v6.12-
> > > > > rc1 on the i.MX8MP PHYTEC Pollux using the
> > > > > arch/arm64/boot/dts/freescale/imx8mp-phyboard-pollux-rdk.dts.
> > > > > The
> > > > > display is the edt,etml1010g3dra panel, as per the upstream
> > > > > dts. We
> > > > > bisected to this commit, and reverting this change fixed the
> > > > > screen.
> > > > > 
> > > > > We then tried to retest this on top of v6.12-rc2, and found
> > > > > we also
> > > > > had
> > > > > to revert commit ff06ea04e4cf3ba2f025024776e83bfbdfa05155
> > > > > ("clk:
> > > > > imx:
> > > > > clk-imx8mp: Allow media_disp pixel clock reconfigure parent
> > > > > rate")
> > > > > alongside this. Reverting these two commits makes the display
> > > > > work
> > > > > again at -rc2.
> > > > > 
> > > > > Do you have any suggestions on anything we might be missing
> > > > > on our
> > > > > end?
> > > > > Please let me know if there's anything you'd like me to test
> > > > > as I'm
> > > > > not
> > > > > sure what the underlying fault was here.
> > > > I believe what is going on is that the LCDIF cannot configure
> > > > its
> > > > upstream clock because something else is already using those
> > > > clock
> > > > and
> > > > it set those clock to a specific frequency. LCDIF is now trying
> > > > to
> > > > configure those clock to match the LVDS panel, and it fails, so
> > > > it
> > > > tries
> > > > to set some approximate clock and that is not good enough for
> > > > the
> > > > LVDS
> > > > panel.
> > > > 
> > > > Can you share dump of /sys/kernel/debug/clk/clk_summary on
> > > > failing
> > > > and
> > > > working system ? You might see the difference around the
> > > > "video"
> > > > clock.
> > > > 
> > > > (I have seen this behavior before, the fix was usually a matter
> > > > of
> > > > moving one of the LCDIFs to another upstream clock like PLL3,
> > > > so it
> > > > can
> > > > pick well matching output clock instead of some horrid
> > > > approximation
> > > > which then drives the panel likely out of specification)
> > > 
> > > Hi Marek,
> > > 
> > > Please find attached the clk_summary for v6.12-rc2 before and
> > > after the
> > > reversion (the one after the reversion is 6.12-
> > > rc2_summary_postfix).
> > Thank you, this helped greatly.
> > 
> > I believe I know why it used to kind-of work for you, but I'm
> > afraid this used to work by sheer chance and it does not really
> > work correctly for the panel you use, even if the panel likely does
> > show the correct content. But, there is a way to make it work
> > properly for the panel you use.
> > 
> > First of all, the pixel clock never really matched the panel-
> > simple.c pixel clock for the edt_etml1010g3dra_timing:
> > 
> > $ grep '\<media_disp2_pix\>' 6.12-rc2_summary_postfix
> >   media_disp2_pix  1  1  0  74250000 ...
> >                             ^^^^^^^^
> > 
> > $ grep -A 1 edt_etml1010g3dra_timing drivers/gpu/drm/panel/panel-
> > simple.c
> > static const struct display_timing edt_etml1010g3dra_timing = {
> >         .pixelclock = { 66300000, 72400000, 78900000 },
> >                                   ^^^^^^^^
> > 
> > The pixel clock are within tolerance, but there is a discrepancy
> > 74250000 != 72400000 .
> > 
> > Since commit 94e6197dadc9 ("arm64: dts: imx8mp: Add LCDIF2 & LDB
> > nodes") the IMX8MP_VIDEO_PLL1_OUT is set to a very specific
> > frequency of 1039500000 Hz, which tidily divides by 2 to 519750000
> > Hz (which is your LVDS serializer frequency) and divides by 7 to
> > 74250000 Hz which is your LCDIF pixel clock.
> > 
> > This Video PLL1 configuration since moved to &media_blk_ctrl {} ,
> > but it is still in the imx8mp.dtsi . Therefore, to make your panel
> > work at the correct desired pixel clock frequency instead of some
> > random one inherited from imx8mp.dtsi, add the following to the
> > pollux DT, I believe that will fix the problem and is the correct
> > fix:
> > 
> > &media_blk_ctrl {
> >    // 506800000 = 72400000 * 7 (for single-link LVDS, this is
> > enough)
> >    // there is no need to multiply the clock by * 2
> >    assigned-clock-rates = <500000000>, <200000000>, <0>, <0>,
> > <500000000>, <506800000>;
> 
> This assigns "video_pll1" clock rate to 506.8MHz which is currently
> not
> listed in imx_pll1443x_tbl[].
> 
> Does the below patch[1] fix the regression issue? It explicitly sets
> the clock frequency of the panel timing to 74.25MHz.
> 
> [1]
> https://patchwork.freedesktop.org/patch/616905/?series=139266&rev=1
> 
> > };
> > 
> > Can you please test whether this works and the pixel clock are
> > accurate in /sys/kernel/debug/clk/clk_summary ?
> > 
> > Now ... as for the LVDS serializer clock ... that is more
> > complicated.
> > 
> > The LCDIF driver does its .atomic_enable first , configures the
> > pixel clock (and the Video PLL now) and enables the clock. The LVDS
> > LDB serializer driver does its .atomic_enable second and cannot
> > reconfigure the clock anymore, the Video PLL is stuck at /7 rate
> > set by LCDIF driver and won't budge because the clock are already
> > enabled. I'm currently trying to figure out if this can be improved
> > somehow, but I believe that would be material for next release.
> > 
> 

This patch also fixes the regression!
Tested-by: Isaac Scott <isaac.scott@ideasonboard.com>