[PATCH 1/2] drm/msm/dsi: fix bits_per_pclk

[PATCH 1/2] drm/msm/dsi: fix bits_per_pclk

[Pengyu Luo]

mipi_dsi_pixel_format_to_bpp return dst bpp not src bpp, dst bpp may
not be the uncompressed data size. use src bpc * 3 to get src bpp,
this aligns with pclk rate calculation.

Fixes: ac47870fd795 ("drm/msm/dsi: fix hdisplay calculation when programming dsi registers")
Signed-off-by: Pengyu Luo <mitltlatltl@gmail.com>
---
 drivers/gpu/drm/msm/dsi/dsi_host.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c b/drivers/gpu/drm/msm/dsi/dsi_host.c
index e8e83ee61e..7c16216e8b 100644
--- a/drivers/gpu/drm/msm/dsi/dsi_host.c
+++ b/drivers/gpu/drm/msm/dsi/dsi_host.c
@@ -1030,7 +1030,7 @@ static void dsi_timing_setup(struct msm_dsi_host *msm_host, bool is_bonded_dsi)
 		 */
 		h_total -= hdisplay;
 		if (wide_bus_enabled)
-			bits_per_pclk = mipi_dsi_pixel_format_to_bpp(msm_host->format);
+			bits_per_pclk = dsc->bits_per_component * 3;
 		else
 			bits_per_pclk = 24;
 
-- 
2.53.0

[PATCH 2/2] drm/msm/dsi: fix hdisplay calculation for CMD mode panel

[Pengyu Luo]

ac47870fd795 incorrecly broke hdisplay calculation for CMD mode, fix
it.

Fixes: ac47870fd795 ("drm/msm/dsi: fix hdisplay calculation when programming dsi registers")
Signed-off-by: Pengyu Luo <mitltlatltl@gmail.com>
---
 drivers/gpu/drm/msm/dsi/dsi_host.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c b/drivers/gpu/drm/msm/dsi/dsi_host.c
index 7c16216e8b..f63165c7ce 100644
--- a/drivers/gpu/drm/msm/dsi/dsi_host.c
+++ b/drivers/gpu/drm/msm/dsi/dsi_host.c
@@ -1016,8 +1016,9 @@ static void dsi_timing_setup(struct msm_dsi_host *msm_host, bool is_bonded_dsi)
 		/*
 		 * DPU sends 3 bytes per pclk cycle to DSI. If widebus is
 		 * enabled, MDP always sends out 48-bit compressed data per
-		 * pclk and on average, DSI consumes an amount of compressed
-		 * data equivalent to the uncompressed pixel depth per pclk.
+		 * pclk and on average, for video mode, DSI consumes only an
+		 * amount of compressed data equivalent to the uncompressed
+		 * pixel depth per pclk.
 		 *
 		 * Calculate the number of pclks needed to transmit one line of
 		 * the compressed data.
@@ -1029,10 +1030,14 @@ static void dsi_timing_setup(struct msm_dsi_host *msm_host, bool is_bonded_dsi)
 		 * unused anyway.
 		 */
 		h_total -= hdisplay;
-		if (wide_bus_enabled)
-			bits_per_pclk = dsc->bits_per_component * 3;
-		else
+		if (wide_bus_enabled) {
+			if (msm_host->mode_flags & MIPI_DSI_MODE_VIDEO)
+				bits_per_pclk = dsc->bits_per_component * 3;
+			else
+				bits_per_pclk = 48;
+		} else {
 			bits_per_pclk = 24;
+		}
 
 		hdisplay = DIV_ROUND_UP(msm_dsc_get_bytes_per_line(msm_host->dsc) * 8, bits_per_pclk);
 
-- 
2.53.0

Re: [PATCH 1/2] drm/msm/dsi: fix bits_per_pclk

[Dmitry Baryshkov]

On Sat, Mar 07, 2026 at 07:12:48PM +0800, Pengyu Luo wrote:
> mipi_dsi_pixel_format_to_bpp return dst bpp not src bpp, dst bpp may
> not be the uncompressed data size. use src bpc * 3 to get src bpp,
> this aligns with pclk rate calculation.
> 
> Fixes: ac47870fd795 ("drm/msm/dsi: fix hdisplay calculation when programming dsi registers")
> Signed-off-by: Pengyu Luo <mitltlatltl@gmail.com>
> ---
>  drivers/gpu/drm/msm/dsi/dsi_host.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Pengyu, what is your target platform?

> 
> diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c b/drivers/gpu/drm/msm/dsi/dsi_host.c
> index e8e83ee61e..7c16216e8b 100644
> --- a/drivers/gpu/drm/msm/dsi/dsi_host.c
> +++ b/drivers/gpu/drm/msm/dsi/dsi_host.c
> @@ -1030,7 +1030,7 @@ static void dsi_timing_setup(struct msm_dsi_host *msm_host, bool is_bonded_dsi)
>  		 */
>  		h_total -= hdisplay;
>  		if (wide_bus_enabled)
> -			bits_per_pclk = mipi_dsi_pixel_format_to_bpp(msm_host->format);
> +			bits_per_pclk = dsc->bits_per_component * 3;
>  		else
>  			bits_per_pclk = 24;
>  
> -- 
> 2.53.0
> 

-- 
With best wishes
Dmitry

Re: [PATCH 1/2] drm/msm/dsi: fix bits_per_pclk

[Pengyu Luo]

On Fri, Mar 20, 2026 at 9:48 AM Dmitry Baryshkov
<dmitry.baryshkov@oss.qualcomm.com> wrote:
>
> On Sat, Mar 07, 2026 at 07:12:48PM +0800, Pengyu Luo wrote:
> > mipi_dsi_pixel_format_to_bpp return dst bpp not src bpp, dst bpp may
> > not be the uncompressed data size. use src bpc * 3 to get src bpp,
> > this aligns with pclk rate calculation.
> >
> > Fixes: ac47870fd795 ("drm/msm/dsi: fix hdisplay calculation when programming dsi registers")
> > Signed-off-by: Pengyu Luo <mitltlatltl@gmail.com>
> > ---
> >  drivers/gpu/drm/msm/dsi/dsi_host.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
>
> Pengyu, what is your target platform?
>

SM8750, my device is lenovo legion y700 gen4, the display is a native
10-bit video mode panel.
Recently, in 10-bit input bpc/30-bit src bpp with 8-bit output
bpc/24-bit dst bpp mode, works well
on this device with some hacks to intf block. full 10-bit input and
output won't work for now.

Once I added this comment in ac47870fd795 ("drm/msm/dsi: fix hdisplay
calculation when programming dsi registers")
> DSI consumes an amount of compressed data equivalent to the uncompressed pixel depth per pclk.
This explanation is picked up from the downstream msm kernel, since
there is no public datasheet for the hardware.
And this should be the video mode case, cmd mode should consume 6
bytes. (It seems no explanation)

If we follow the downstream, then the uncompressed pixel depth per
pclk should be 3 * bits_per_component.
This is what this patch fixed.

About the test, I did it on the video mode panel, I have no cmd panel
device with dsc/widen bus enabled. And I overlooked something, I
thought
cmd panel didn't use hdisplay, then I removed the right value for the
cmd panel case, I fixed it in patch 2/2.

Best wishes,
Pengyu


> >
> > diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c b/drivers/gpu/drm/msm/dsi/dsi_host.c
> > index e8e83ee61e..7c16216e8b 100644
> > --- a/drivers/gpu/drm/msm/dsi/dsi_host.c
> > +++ b/drivers/gpu/drm/msm/dsi/dsi_host.c
> > @@ -1030,7 +1030,7 @@ static void dsi_timing_setup(struct msm_dsi_host *msm_host, bool is_bonded_dsi)
> >                */
> >               h_total -= hdisplay;
> >               if (wide_bus_enabled)
> > -                     bits_per_pclk = mipi_dsi_pixel_format_to_bpp(msm_host->format);
> > +                     bits_per_pclk = dsc->bits_per_component * 3;
> >               else
> >                       bits_per_pclk = 24;
> >
> > --
> > 2.53.0
> >
>
> --
> With best wishes
> Dmitry

Re: [PATCH 1/2] drm/msm/dsi: fix bits_per_pclk

[Dmitry Baryshkov]

On Sat, 07 Mar 2026 19:12:48 +0800, Pengyu Luo wrote:
> mipi_dsi_pixel_format_to_bpp return dst bpp not src bpp, dst bpp may
> not be the uncompressed data size. use src bpc * 3 to get src bpp,
> this aligns with pclk rate calculation.

Applied to msm-next, thanks!

[1/2] drm/msm/dsi: fix bits_per_pclk
      https://gitlab.freedesktop.org/lumag/msm/-/commit/2d51cfb77daa
[2/2] drm/msm/dsi: fix hdisplay calculation for CMD mode panel
      https://gitlab.freedesktop.org/lumag/msm/-/commit/82159db4371f

Best regards,
-- 
With best wishes
Dmitry

Re: [PATCH 2/2] drm/msm/dsi: fix hdisplay calculation for CMD mode panel

[Marijn Suijten]

On 2026-03-07 19:12:49, Pengyu Luo wrote:
> ac47870fd795 incorrecly broke hdisplay calculation for CMD mode, fix
> it.

Where's the what/how/why?  This commit message explains exactly nothing while a
description is a requirement for submitting patches upstream:

https://docs.kernel.org/process/submitting-patches.html#describe-your-changes

Take my version of this patch as an example.

> 
> Fixes: ac47870fd795 ("drm/msm/dsi: fix hdisplay calculation when programming dsi registers")
> Signed-off-by: Pengyu Luo <mitltlatltl@gmail.com>
> ---
>  drivers/gpu/drm/msm/dsi/dsi_host.c | 15 ++++++++++-----
>  1 file changed, 10 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c b/drivers/gpu/drm/msm/dsi/dsi_host.c
> index 7c16216e8b..f63165c7ce 100644
> --- a/drivers/gpu/drm/msm/dsi/dsi_host.c
> +++ b/drivers/gpu/drm/msm/dsi/dsi_host.c
> @@ -1016,8 +1016,9 @@ static void dsi_timing_setup(struct msm_dsi_host *msm_host, bool is_bonded_dsi)
>  		/*
>  		 * DPU sends 3 bytes per pclk cycle to DSI. If widebus is
>  		 * enabled, MDP always sends out 48-bit compressed data per
> -		 * pclk and on average, DSI consumes an amount of compressed
> -		 * data equivalent to the uncompressed pixel depth per pclk.
> +		 * pclk and on average, for video mode, DSI consumes only an
> +		 * amount of compressed data equivalent to the uncompressed
> +		 * pixel depth per pclk.

This needs a source and justification (in the commit message).  For most
panels where bpc is simply 8, the resulting rate is the same as when widebus is
disabled, meaning that widebus has no effect on the pclk rate in video-mode?

- Marijn

>  		 *
>  		 * Calculate the number of pclks needed to transmit one line of
>  		 * the compressed data.
> @@ -1029,10 +1030,14 @@ static void dsi_timing_setup(struct msm_dsi_host *msm_host, bool is_bonded_dsi)
>  		 * unused anyway.
>  		 */
>  		h_total -= hdisplay;
> -		if (wide_bus_enabled)
> -			bits_per_pclk = dsc->bits_per_component * 3;
> -		else
> +		if (wide_bus_enabled) {
> +			if (msm_host->mode_flags & MIPI_DSI_MODE_VIDEO)
> +				bits_per_pclk = dsc->bits_per_component * 3;
> +			else
> +				bits_per_pclk = 48;
> +		} else {
>  			bits_per_pclk = 24;
> +		}
>  
>  		hdisplay = DIV_ROUND_UP(msm_dsc_get_bytes_per_line(msm_host->dsc) * 8, bits_per_pclk);
>  
> -- 
> 2.53.0
> 

Re: [PATCH 1/2] drm/msm/dsi: fix bits_per_pclk

[Luca Weiss]

Hi all,

On Fri Mar 27, 2026 at 8:47 PM CET, Dmitry Baryshkov wrote:
> On Sat, 07 Mar 2026 19:12:48 +0800, Pengyu Luo wrote:
>> mipi_dsi_pixel_format_to_bpp return dst bpp not src bpp, dst bpp may
>> not be the uncompressed data size. use src bpc * 3 to get src bpp,
>> this aligns with pclk rate calculation.
>
> Applied to msm-next, thanks!
>
> [1/2] drm/msm/dsi: fix bits_per_pclk
>       https://gitlab.freedesktop.org/lumag/msm/-/commit/2d51cfb77daa
> [2/2] drm/msm/dsi: fix hdisplay calculation for CMD mode panel
>       https://gitlab.freedesktop.org/lumag/msm/-/commit/82159db4371f

Just wanna document this somewhere, 7.0 is quite broken on QCM6490
Fairphone 5 (8-bit cmd mode panel).

Picking these two patches plus "drm/msm/dpu: don't try using 2 LMs if
only one DSC is available" on top of 7.0 makes display work again.

Regards
Luca

Re: [PATCH 1/2] drm/msm/dsi: fix bits_per_pclk

[Dmitry Baryshkov]

On Tue, Apr 14, 2026 at 12:13:45PM +0200, Luca Weiss wrote:
> Hi all,
> 
> On Fri Mar 27, 2026 at 8:47 PM CET, Dmitry Baryshkov wrote:
> > On Sat, 07 Mar 2026 19:12:48 +0800, Pengyu Luo wrote:
> >> mipi_dsi_pixel_format_to_bpp return dst bpp not src bpp, dst bpp may
> >> not be the uncompressed data size. use src bpc * 3 to get src bpp,
> >> this aligns with pclk rate calculation.
> >
> > Applied to msm-next, thanks!
> >
> > [1/2] drm/msm/dsi: fix bits_per_pclk
> >       https://gitlab.freedesktop.org/lumag/msm/-/commit/2d51cfb77daa
> > [2/2] drm/msm/dsi: fix hdisplay calculation for CMD mode panel
> >       https://gitlab.freedesktop.org/lumag/msm/-/commit/82159db4371f
> 
> Just wanna document this somewhere, 7.0 is quite broken on QCM6490
> Fairphone 5 (8-bit cmd mode panel).
> 
> Picking these two patches plus "drm/msm/dpu: don't try using 2 LMs if
> only one DSC is available" on top of 7.0 makes display work again.

Yep. It was a bit too late for 7.0, so the plan (and hope) is for them
to be picked up into 7.0-stable.

-- 
With best wishes
Dmitry