Re: [PATCH] drm/rcar-du: dsi: Handle both DRM_MODE_FLAG_N.SYNC and !DRM_MODE_FLAG_P.SYNC
From: Marek Vasut
Date: Tue Nov 25 2025 - 15:14:43 EST
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 .
[...]
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./* 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;