[PATCH] drm/rcar-du: dsi: Handle both DRM_MODE_FLAG_N.SYNC and !DRM_MODE_FLAG_P.SYNC

[PATCH] drm/rcar-du: dsi: Handle both DRM_MODE_FLAG_N.SYNC and !DRM_MODE_FLAG_P.SYNC

[Marek Vasut]

Since commit 94fe479fae96 ("drm/rcar-du: dsi: Clean up handling of DRM mode flags")
the driver does not set TXVMVPRMSET0R_VSPOL_LOW and TXVMVPRMSET0R_HSPOL_LOW
for modes which set neither DRM_MODE_FLAG_[PN].SYNC. The previous behavior
was to assume that neither flag means DRM_MODE_FLAG_N.SYNC . Restore the
previous behavior for maximum compatibility.

Fixes: 94fe479fae96 ("drm/rcar-du: dsi: Clean up handling of DRM mode flags")
Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
---
Cc: David Airlie <airlied@gmail.com>
Cc: Geert Uytterhoeven <geert+renesas@glider.be>
Cc: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Cc: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Magnus Damm <magnus.damm@gmail.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Simona Vetter <simona@ffwll.ch>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Tomi Valkeinen <tomi.valkeinen+renesas@ideasonboard.com>
Cc: dri-devel@lists.freedesktop.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-renesas-soc@vger.kernel.org
---
 drivers/gpu/drm/renesas/rcar-du/rcar_mipi_dsi.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/renesas/rcar-du/rcar_mipi_dsi.c b/drivers/gpu/drm/renesas/rcar-du/rcar_mipi_dsi.c
index 9413b76d0bfce..98bd7f40adbea 100644
--- a/drivers/gpu/drm/renesas/rcar-du/rcar_mipi_dsi.c
+++ b/drivers/gpu/drm/renesas/rcar-du/rcar_mipi_dsi.c
@@ -492,9 +492,11 @@ static void rcar_mipi_dsi_set_display_timing(struct rcar_mipi_dsi *dsi,
 
 	/* Configuration for Video Parameters, input is always RGB888 */
 	vprmset0r = TXVMVPRMSET0R_BPP_24;
-	if (mode->flags & DRM_MODE_FLAG_NVSYNC)
+	if ((mode->flags & DRM_MODE_FLAG_NVSYNC) ||
+	    !(mode->flags & DRM_MODE_FLAG_PVSYNC))
 		vprmset0r |= TXVMVPRMSET0R_VSPOL_LOW;
-	if (mode->flags & DRM_MODE_FLAG_NHSYNC)
+	if ((mode->flags & DRM_MODE_FLAG_NHSYNC) ||
+	    !(mode->flags & DRM_MODE_FLAG_PHSYNC))
 		vprmset0r |= TXVMVPRMSET0R_HSPOL_LOW;
 
 	vprmset1r = TXVMVPRMSET1R_VACTIVE(mode->vdisplay)
-- 
2.51.0

Re: [PATCH] drm/rcar-du: dsi: Handle both DRM_MODE_FLAG_N.SYNC and !DRM_MODE_FLAG_P.SYNC

[Laurent Pinchart]

On Sat, Nov 08, 2025 at 12:04:10AM +0100, Marek Vasut wrote:
> Since commit 94fe479fae96 ("drm/rcar-du: dsi: Clean up handling of DRM mode flags")
> the driver does not set TXVMVPRMSET0R_VSPOL_LOW and TXVMVPRMSET0R_HSPOL_LOW
> for modes which set neither DRM_MODE_FLAG_[PN].SYNC.

Could you please explain what broke ? What panel are you using ?

> The previous behavior
> was to assume that neither flag means DRM_MODE_FLAG_N.SYNC . Restore the
> previous behavior for maximum compatibility.
> 
> Fixes: 94fe479fae96 ("drm/rcar-du: dsi: Clean up handling of DRM mode flags")
> Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
> ---
> Cc: David Airlie <airlied@gmail.com>
> Cc: Geert Uytterhoeven <geert+renesas@glider.be>
> Cc: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
> Cc: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> Cc: Magnus Damm <magnus.damm@gmail.com>
> Cc: Maxime Ripard <mripard@kernel.org>
> Cc: Simona Vetter <simona@ffwll.ch>
> Cc: Thomas Zimmermann <tzimmermann@suse.de>
> Cc: Tomi Valkeinen <tomi.valkeinen+renesas@ideasonboard.com>
> Cc: dri-devel@lists.freedesktop.org
> Cc: linux-kernel@vger.kernel.org
> Cc: linux-renesas-soc@vger.kernel.org
> ---
>  drivers/gpu/drm/renesas/rcar-du/rcar_mipi_dsi.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/renesas/rcar-du/rcar_mipi_dsi.c b/drivers/gpu/drm/renesas/rcar-du/rcar_mipi_dsi.c
> index 9413b76d0bfce..98bd7f40adbea 100644
> --- a/drivers/gpu/drm/renesas/rcar-du/rcar_mipi_dsi.c
> +++ b/drivers/gpu/drm/renesas/rcar-du/rcar_mipi_dsi.c
> @@ -492,9 +492,11 @@ static void rcar_mipi_dsi_set_display_timing(struct rcar_mipi_dsi *dsi,
>  
>  	/* Configuration for Video Parameters, input is always RGB888 */
>  	vprmset0r = TXVMVPRMSET0R_BPP_24;
> -	if (mode->flags & DRM_MODE_FLAG_NVSYNC)
> +	if ((mode->flags & DRM_MODE_FLAG_NVSYNC) ||
> +	    !(mode->flags & DRM_MODE_FLAG_PVSYNC))
>  		vprmset0r |= TXVMVPRMSET0R_VSPOL_LOW;

I don't think this restores the previous behaviour. You would need to
write

	if (!(mode->flags & DRM_MODE_FLAG_PVSYNC))
		vprmset0r |= TXVMVPRMSET0R_VSPOL_LOW;

> -	if (mode->flags & DRM_MODE_FLAG_NHSYNC)
> +	if ((mode->flags & DRM_MODE_FLAG_NHSYNC) ||
> +	    !(mode->flags & DRM_MODE_FLAG_PHSYNC))
>  		vprmset0r |= TXVMVPRMSET0R_HSPOL_LOW;

Same here.

>  
>  	vprmset1r = TXVMVPRMSET1R_VACTIVE(mode->vdisplay)

-- 
Regards,

Laurent Pinchart

Re: [PATCH] drm/rcar-du: dsi: Handle both DRM_MODE_FLAG_N.SYNC and !DRM_MODE_FLAG_P.SYNC

[Marek Vasut]

On 11/8/25 12:23 AM, Laurent Pinchart wrote:
> On Sat, Nov 08, 2025 at 12:04:10AM +0100, Marek Vasut wrote:
>> Since commit 94fe479fae96 ("drm/rcar-du: dsi: Clean up handling of DRM mode flags")
>> the driver does not set TXVMVPRMSET0R_VSPOL_LOW and TXVMVPRMSET0R_HSPOL_LOW
>> for modes which set neither DRM_MODE_FLAG_[PN].SYNC.
> 
> Could you please explain what broke ?

Consider mode->flags, V-ones for simplicity:

Before 94fe479fae96 :

DRM_MODE_FLAG_PVSYNC => vprmset0r |= 0
DRM_MODE_FLAG_NVSYNC => vprmset0r |= TXVMVPRMSET0R_VSPOL_LOW
Neither DRM_MODE_FLAG_[PN]VSYNC => vprmset0r |= TXVMVPRMSET0R_VSPOL_LOW

After 94fe479fae96 :

DRM_MODE_FLAG_PVSYNC => vprmset0r |= 0
DRM_MODE_FLAG_NVSYNC => vprmset0r |= TXVMVPRMSET0R_VSPOL_LOW
Neither DRM_MODE_FLAG_[PN]VSYNC => vprmset0r |= 0 <---------- This broke

The "Neither" case behavior is different. I did not realize that:

DRM_MODE_FLAG_N[HV]SYNC is not equivalent !DRM_MODE_FLAG_P[HV]SYNC

They really are not equivalent .

[...]

>>   	/* Configuration for Video Parameters, input is always RGB888 */
>>   	vprmset0r = TXVMVPRMSET0R_BPP_24;
>> -	if (mode->flags & DRM_MODE_FLAG_NVSYNC)
>> +	if ((mode->flags & DRM_MODE_FLAG_NVSYNC) ||
>> +	    !(mode->flags & DRM_MODE_FLAG_PVSYNC))
>>   		vprmset0r |= TXVMVPRMSET0R_VSPOL_LOW;
> 
> I don't think this restores the previous behaviour. You would need to
> write
> 
> 	if (!(mode->flags & DRM_MODE_FLAG_PVSYNC))
> 		vprmset0r |= TXVMVPRMSET0R_VSPOL_LOW;
This patch covers both the N[HV]SYNC and !P[HV]SYNC , so that should 
restore the behavior to "Before" and explicitly be clear that N[HV]SYNC 
and !P[HV]SYNC are not the same thing.

Re: [PATCH] drm/rcar-du: dsi: Handle both DRM_MODE_FLAG_N.SYNC and !DRM_MODE_FLAG_P.SYNC

[Laurent Pinchart]

Hi Marek,

On Tue, Nov 25, 2025 at 09:13:02PM +0100, Marek Vasut wrote:
> On 11/8/25 12:23 AM, Laurent Pinchart wrote:
> > On Sat, Nov 08, 2025 at 12:04:10AM +0100, Marek Vasut wrote:
> >> Since commit 94fe479fae96 ("drm/rcar-du: dsi: Clean up handling of DRM mode flags")
> >> the driver does not set TXVMVPRMSET0R_VSPOL_LOW and TXVMVPRMSET0R_HSPOL_LOW
> >> for modes which set neither DRM_MODE_FLAG_[PN].SYNC.
> > 
> > Could you please explain what broke ?

Sorry, I wasn't clear. I meant could you summarize the explanation in
the commit message ?

> Consider mode->flags, V-ones for simplicity:
> 
> Before 94fe479fae96 :
> 
> DRM_MODE_FLAG_PVSYNC => vprmset0r |= 0
> DRM_MODE_FLAG_NVSYNC => vprmset0r |= TXVMVPRMSET0R_VSPOL_LOW
> Neither DRM_MODE_FLAG_[PN]VSYNC => vprmset0r |= TXVMVPRMSET0R_VSPOL_LOW
> 
> After 94fe479fae96 :
> 
> DRM_MODE_FLAG_PVSYNC => vprmset0r |= 0
> DRM_MODE_FLAG_NVSYNC => vprmset0r |= TXVMVPRMSET0R_VSPOL_LOW
> Neither DRM_MODE_FLAG_[PN]VSYNC => vprmset0r |= 0 <---------- This broke
> 
> The "Neither" case behavior is different. I did not realize that:
> 
> DRM_MODE_FLAG_N[HV]SYNC is not equivalent !DRM_MODE_FLAG_P[HV]SYNC
> 
> They really are not equivalent .
> 
> [...]
> 
> >>   	/* Configuration for Video Parameters, input is always RGB888 */
> >>   	vprmset0r = TXVMVPRMSET0R_BPP_24;
> >> -	if (mode->flags & DRM_MODE_FLAG_NVSYNC)
> >> +	if ((mode->flags & DRM_MODE_FLAG_NVSYNC) ||
> >> +	    !(mode->flags & DRM_MODE_FLAG_PVSYNC))
> >>   		vprmset0r |= TXVMVPRMSET0R_VSPOL_LOW;
> > 
> > I don't think this restores the previous behaviour. You would need to
> > write
> > 
> > 	if (!(mode->flags & DRM_MODE_FLAG_PVSYNC))
> > 		vprmset0r |= TXVMVPRMSET0R_VSPOL_LOW;
>
> This patch covers both the N[HV]SYNC and !P[HV]SYNC , so that should 
> restore the behavior to "Before" and explicitly be clear that N[HV]SYNC 
> and !P[HV]SYNC are not the same thing.

Before commit 94fe479fae96 we had

	vprmset0r = (mode->flags & DRM_MODE_FLAG_PVSYNC ?
		     TXVMVPRMSET0R_VSPOL_HIG : TXVMVPRMSET0R_VSPOL_LOW)
		  | (mode->flags & DRM_MODE_FLAG_PHSYNC ?
		     TXVMVPRMSET0R_HSPOL_HIG : TXVMVPRMSET0R_HSPOL_LOW)
		  | TXVMVPRMSET0R_CSPC_RGB | TXVMVPRMSET0R_BPP_24;

Considering the vertical sync for simplicity, this gives us

NVSYNC \ PVSYNC		0		1
 0			VSPOL_LOW	VSPOL_HIG
 1			VSPOL_LOW	VSPOL_HIG

With this patch, the code becomes

	/* Configuration for Video Parameters, input is always RGB888 */
	vprmset0r = TXVMVPRMSET0R_BPP_24;
	if ((mode->flags & DRM_MODE_FLAG_NVSYNC) ||
	    !(mode->flags & DRM_MODE_FLAG_PVSYNC))
		vprmset0r |= TXVMVPRMSET0R_VSPOL_LOW;
	if ((mode->flags & DRM_MODE_FLAG_NHSYNC) ||
	    !(mode->flags & DRM_MODE_FLAG_PHSYNC))
		vprmset0r |= TXVMVPRMSET0R_HSPOL_LOW;

which gives us

NVSYNC \ PVSYNC		0		1
 0			VSPOL_LOW	VSPOL_HIG
 1			VSPOL_LOW	VSPOL_LOW

This is a different behaviour. Granted, we should never have both NVSYNC
and PVSYNC set together (unless I'm missing something), so the
difference in behaviour shouldn't matter. I'm fine with that if you
explain it in the commit message, however I think that writing

 	if (!(mode->flags & DRM_MODE_FLAG_PVSYNC))
 		vprmset0r |= TXVMVPRMSET0R_VSPOL_LOW;
 	if (!(mode->flags & DRM_MODE_FLAG_PHSYNC))
 		vprmset0r |= TXVMVPRMSET0R_HSPOL_LOW;

would both restore the previous behaviour in all cases, and be simpler.

-- 
Regards,

Laurent Pinchart

Re: [PATCH] drm/rcar-du: dsi: Handle both DRM_MODE_FLAG_N.SYNC and !DRM_MODE_FLAG_P.SYNC

[Marek Vasut]

On 12/1/25 7:09 AM, Laurent Pinchart wrote:

Hello Laurent,

> On Tue, Nov 25, 2025 at 09:13:02PM +0100, Marek Vasut wrote:
>> On 11/8/25 12:23 AM, Laurent Pinchart wrote:
>>> On Sat, Nov 08, 2025 at 12:04:10AM +0100, Marek Vasut wrote:
>>>> Since commit 94fe479fae96 ("drm/rcar-du: dsi: Clean up handling of DRM mode flags")
>>>> the driver does not set TXVMVPRMSET0R_VSPOL_LOW and TXVMVPRMSET0R_HSPOL_LOW
>>>> for modes which set neither DRM_MODE_FLAG_[PN].SYNC.
>>>
>>> Could you please explain what broke ?
> 
> Sorry, I wasn't clear. I meant could you summarize the explanation in
> the commit message ?
> 
>> Consider mode->flags, V-ones for simplicity:
>>
>> Before 94fe479fae96 :
>>
>> DRM_MODE_FLAG_PVSYNC => vprmset0r |= 0
>> DRM_MODE_FLAG_NVSYNC => vprmset0r |= TXVMVPRMSET0R_VSPOL_LOW
>> Neither DRM_MODE_FLAG_[PN]VSYNC => vprmset0r |= TXVMVPRMSET0R_VSPOL_LOW
>>
>> After 94fe479fae96 :
>>
>> DRM_MODE_FLAG_PVSYNC => vprmset0r |= 0
>> DRM_MODE_FLAG_NVSYNC => vprmset0r |= TXVMVPRMSET0R_VSPOL_LOW
>> Neither DRM_MODE_FLAG_[PN]VSYNC => vprmset0r |= 0 <---------- This broke
>>
>> The "Neither" case behavior is different. I did not realize that:
>>
>> DRM_MODE_FLAG_N[HV]SYNC is not equivalent !DRM_MODE_FLAG_P[HV]SYNC
>>
>> They really are not equivalent .
>>
>> [...]
>>
>>>>    	/* Configuration for Video Parameters, input is always RGB888 */
>>>>    	vprmset0r = TXVMVPRMSET0R_BPP_24;
>>>> -	if (mode->flags & DRM_MODE_FLAG_NVSYNC)
>>>> +	if ((mode->flags & DRM_MODE_FLAG_NVSYNC) ||
>>>> +	    !(mode->flags & DRM_MODE_FLAG_PVSYNC))
>>>>    		vprmset0r |= TXVMVPRMSET0R_VSPOL_LOW;
>>>
>>> I don't think this restores the previous behaviour. You would need to
>>> write
>>>
>>> 	if (!(mode->flags & DRM_MODE_FLAG_PVSYNC))
>>> 		vprmset0r |= TXVMVPRMSET0R_VSPOL_LOW;
>>
>> This patch covers both the N[HV]SYNC and !P[HV]SYNC , so that should
>> restore the behavior to "Before" and explicitly be clear that N[HV]SYNC
>> and !P[HV]SYNC are not the same thing.
> 
> Before commit 94fe479fae96 we had
> 
> 	vprmset0r = (mode->flags & DRM_MODE_FLAG_PVSYNC ?
> 		     TXVMVPRMSET0R_VSPOL_HIG : TXVMVPRMSET0R_VSPOL_LOW)
> 		  | (mode->flags & DRM_MODE_FLAG_PHSYNC ?
> 		     TXVMVPRMSET0R_HSPOL_HIG : TXVMVPRMSET0R_HSPOL_LOW)
> 		  | TXVMVPRMSET0R_CSPC_RGB | TXVMVPRMSET0R_BPP_24;
> 
> Considering the vertical sync for simplicity, this gives us
> 
> NVSYNC \ PVSYNC		0		1
>   0			VSPOL_LOW	VSPOL_HIG
>   1			VSPOL_LOW	VSPOL_HIG
> 
> With this patch, the code becomes
> 
> 	/* Configuration for Video Parameters, input is always RGB888 */
> 	vprmset0r = TXVMVPRMSET0R_BPP_24;
> 	if ((mode->flags & DRM_MODE_FLAG_NVSYNC) ||
> 	    !(mode->flags & DRM_MODE_FLAG_PVSYNC))
> 		vprmset0r |= TXVMVPRMSET0R_VSPOL_LOW;
> 	if ((mode->flags & DRM_MODE_FLAG_NHSYNC) ||
> 	    !(mode->flags & DRM_MODE_FLAG_PHSYNC))
> 		vprmset0r |= TXVMVPRMSET0R_HSPOL_LOW;
> 
> which gives us
> 
> NVSYNC \ PVSYNC		0		1
>   0			VSPOL_LOW	VSPOL_HIG
>   1			VSPOL_LOW	VSPOL_LOW
> 
> This is a different behaviour. Granted, we should never have both NVSYNC
> and PVSYNC set together (unless I'm missing something), so the
> difference in behaviour shouldn't matter. I'm fine with that if you
> explain it in the commit message, however I think that writing
> 
>   	if (!(mode->flags & DRM_MODE_FLAG_PVSYNC))
>   		vprmset0r |= TXVMVPRMSET0R_VSPOL_LOW;
>   	if (!(mode->flags & DRM_MODE_FLAG_PHSYNC))
>   		vprmset0r |= TXVMVPRMSET0R_HSPOL_LOW;
> 
> would both restore the previous behaviour in all cases, and be simpler.
I sent a V2 which addresses both, the commit message update and this 
comment.