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

Heiko Stübner
2023-10-16T18:15:21Z

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].

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

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?

Thanks
Heiko

[0]
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm64/boot/dts/rockchip/px30-evb.dts#n138
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/gpu/drm/panel/panel-xinpeng-xpp055c272.c

> ---
> 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);