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.
