RE: [PATCH 5/9] drm/bridge: synopsys: dw-mipi-dsi: Use pixel clock rate to calculate lbcc

Ying Liu
2023-10-17T10:15:49Z

On Tuesday, October 17, 2023 2:15 AM, Heiko Stübner <heiko@sntech.de> wrote:
> Hi,

Hi,

>
> Am Montag, 17. Juli 2023, 08:18:27 CEST schrieb Liu Ying:
> > To get better accuration, use pixel clock rate to calculate lbcc instead of
> > lane_mbps since the pixel clock rate is in KHz while lane_mbps is in MHz.
> > Without this, distorted image can be seen on a HDMI monitor connected
> with
> > i.MX93 11x11 EVK through ADV7535 DSI to HDMI bridge in 1920x1080p@60
> video
> > mode.
> >
> > Signed-off-by: Liu Ying <victor.liu@nxp.com>
>
> looks like I'm late to the party, but this change breaks the display output
> my px30 minievb with the xinpeng xpp055c272 dsi display [0].

Hmm, I asked for a test, but anyway sorry for the breakage.

The panel driver sets MIPI_DSI_MODE_VIDEO_BURST.
And, it seems that rockchip dsi driver [1] only supports the burst mode,
because it takes 1/0.8 = 1.25 faster lane_mbps than "bandwidth of RGB".

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/gpu/drm/rockchip/dw-mipi-dsi-rockchip.c#n568

>
> Found this commit via git bisection and added a bit of debug output to
> compare the value differences for the old and new calculation:
>
> [ 34.810722] dw_mipi_dsi_get_hcomponent_lbcc: old lbcc: 810 * 480 * 1000
> / 8
> [ 34.810749] dw_mipi_dsi_get_hcomponent_lbcc: new lbcc: 810 * 64000 *
> 24 / (4 * 8)
> [ 34.810756] dw_mipi_dsi_get_hcomponent_lbcc: old lbcc: 48600000, new
> lbcc: 38880000
> [ 34.810762] dw_mipi_dsi_get_hcomponent_lbcc: old lbcc: 10 * 480 * 1000 /
> 8
> [ 34.810767] dw_mipi_dsi_get_hcomponent_lbcc: new lbcc: 10 * 64000 * 24
> / (4 * 8)
> [ 34.810773] dw_mipi_dsi_get_hcomponent_lbcc: old lbcc: 600000, new lbcc:
> 480000
> [ 34.810778] dw_mipi_dsi_get_hcomponent_lbcc: old lbcc: 40 * 480 * 1000 /
> 8
> [ 34.810783] dw_mipi_dsi_get_hcomponent_lbcc: new lbcc: 40 * 64000 * 24
> / (4 * 8)
> [ 34.810789] dw_mipi_dsi_get_hcomponent_lbcc: old lbcc: 2400000, new
> lbcc: 1920000

Old lbcc / new lbcc is always 1.25.

The new lbcc is for non-burst modes(sync pulse/sync event), IIUC.
At least, it works for i.MX93 with the RM67191 panel and ADV7535 in
sync pulse mode.

>
> With the new lbcc I get a blank dsi panel and just going back to the old
> calculation of lbcc restores the image.
>
> I don't have that much in-depth knowledge about dsi stuff and the original
> panel times also "just" came from the vendor tree, but I really would like
> to keep that display working ;-) .
>
> Do you have any idea which way to go to fix this?

Can you please test the below patch for your case?

--------------------------------------------------------8<---------------------------------------------------------------------
--- a/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c
+++ b/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c
@@ -774,13 +774,19 @@ static u32 dw_mipi_dsi_get_hcomponent_lbcc(struct dw_mipi_dsi *dsi,
u32 frac, lbcc, minimum_lbcc;
int bpp;

- bpp = mipi_dsi_pixel_format_to_bpp(dsi->format);
- if (bpp < 0) {
- dev_err(dsi->dev, "failed to get bpp\n");
- return 0;
- }
+ if (dsi->mode_flags & MIPI_DSI_MODE_VIDEO_BURST) {
+ /* lbcc based on lane_mbps */
+ lbcc = hcomponent * dsi->lane_mbps * MSEC_PER_SEC / 8;
+ } else {
+ /* lbcc based on pixel clock */
+ bpp = mipi_dsi_pixel_format_to_bpp(dsi->format);
+ if (bpp < 0) {
+ dev_err(dsi->dev, "failed to get bpp\n");
+ return 0;
+ }

- lbcc = div_u64((u64)hcomponent * mode->clock * bpp, dsi->lanes * 8);
+ lbcc = div_u64((u64)hcomponent * mode->clock * bpp, dsi->lanes * 8);
+ }

frac = lbcc % mode->clock;
lbcc = lbcc / mode->clock;
--------------------------------------------------------8<---------------------------------------------------------------------

It kind of keeps the old lbcc for burst mode, except for the minimum lbcc check
I introduced.

It seems that meson supports non-burst modes only and stm supports both
non-burst modes and burst mode. With the patch, I still worry about non-burst
modes for stm, assuming the minimum lbcc check is ok and everything works
for meson since I guess Neil has already tested the patch set on meson.

Should we go with the above patch? If yes, I may send it out.

Regards,
Liu Ying

>
>
> Thanks
> Heiko
>
>
> [0]
> https://git.ker/
> nel.org%2Fpub%2Fscm%2Flinux%2Fkernel%2Fgit%2Ftorvalds%2Flinux.git%2F
> tree%2Farch%2Farm64%2Fboot%2Fdts%2Frockchip%2Fpx30-
> evb.dts%23n138&data=05%7C01%7Cvictor.liu%40nxp.com%7C8f712ad41720
> 4ba7411808dbce73ce63%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%7C0
> %7C638330769044424464%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLj
> AwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%
> 7C%7C&sdata=effPCbPOk3GGuO8mR%2FSlcjFJfDUEZmq082simvjkux0%3D&r
> eserved=0
> https://git.ker/
> nel.org%2Fpub%2Fscm%2Flinux%2Fkernel%2Fgit%2Ftorvalds%2Flinux.git%2F
> tree%2Fdrivers%2Fgpu%2Fdrm%2Fpanel%2Fpanel-xinpeng-
> xpp055c272.c&data=05%7C01%7Cvictor.liu%40nxp.com%7C8f712ad417204b
> a7411808dbce73ce63%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%7C0%7
> C638330769044424464%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAw
> MDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C
> %7C&sdata=bAgcLnJpIEQaYZZUI1CnUsgP7rMiNV6wKKg%2Bl8%2FlN40%3D&r
> eserved=0
>
> > ---
> > drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c | 10 +++++++++-
> > 1 file changed, 9 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c
> b/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c
> > index c754d55f71d1..332388fd86da 100644
> > --- a/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c
> > +++ b/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c
> > @@ -12,6 +12,7 @@
> > #include <linux/component.h>
> > #include <linux/debugfs.h>
> > #include <linux/iopoll.h>
> > +#include <linux/math64.h>
> > #include <linux/media-bus-format.h>
> > #include <linux/module.h>
> > #include <linux/of_device.h>
> > @@ -762,8 +763,15 @@ static u32
> dw_mipi_dsi_get_hcomponent_lbcc(struct dw_mipi_dsi *dsi,
> > u32 hcomponent)
> > {
> > u32 frac, lbcc;
> > + int bpp;
> >
> > - lbcc = hcomponent * dsi->lane_mbps * MSEC_PER_SEC / 8;
> > + bpp = mipi_dsi_pixel_format_to_bpp(dsi->format);
> > + if (bpp < 0) {
> > + dev_err(dsi->dev, "failed to get bpp\n");
> > + return 0;
> > + }
> > +
> > + lbcc = div_u64((u64)hcomponent * mode->clock * bpp, dsi->lanes *
> 8);