[BUG] HDMI monitor shows no signal when the refresh rate is higher than the default 60Hz

[BUG] HDMI monitor shows no signal when the refresh rate is higher than the default 60Hz

[hgfdgjn]

Hi maintainers:

  After updating to v6.19.6 on Arch Linux, if I set the refresh rate
higher than 60Hz, the monitor displays "No Signal".
I tried bisecting and found:
> # first bad commit: [3471b9a31ce352ffb343cf02a991261880aac3a7] drm/amd/display: Rework HDMI data channel reads

This issue on my machine was caused by this change:

diff --git a/drivers/gpu/drm/amd/display/dc/link/protocols/link_ddc.c
b/drivers/gpu/drm/amd/display/dc/link/protocols/link_ddc.c
index 267180e7bc48..5d2bcce2f669 100644
--- a/drivers/gpu/drm/amd/display/dc/link/protocols/link_ddc.c
+++ b/drivers/gpu/drm/amd/display/dc/link/protocols/link_ddc.c
@@ -549,7 +549,8 @@ void write_scdc_data(struct ddc_service *ddc_service,
     /*Lower than 340 Scramble bit from SCDC caps*/

     if (ddc_service->link->local_sink &&
-        ddc_service->link->local_sink->edid_caps.panel_patch.skip_scdc_overwrite)
+        (ddc_service->link->local_sink->edid_caps.panel_patch.skip_scdc_overwrite
||
+        !ddc_service->link->local_sink->edid_caps.scdc_present))
         return;

     link_query_ddc_data(ddc_service, slave_address, &offset,


It appears that scdc_present is always false on my device.
I reverted the change to write_scdc_data(), and the monitor works
normally at high refresh rates.

Re: [BUG] HDMI monitor shows no signal when the refresh rate is higher than the default 60Hz

[Greg KH]

On Sun, Mar 08, 2026 at 05:42:39PM +0800, hgfdgjn wrote:
> Hi maintainers:
> 
>   After updating to v6.19.6 on Arch Linux, if I set the refresh rate
> higher than 60Hz, the monitor displays "No Signal".
> I tried bisecting and found:
> > # first bad commit: [3471b9a31ce352ffb343cf02a991261880aac3a7] drm/amd/display: Rework HDMI data channel reads
> 
> This issue on my machine was caused by this change:
> 
> diff --git a/drivers/gpu/drm/amd/display/dc/link/protocols/link_ddc.c
> b/drivers/gpu/drm/amd/display/dc/link/protocols/link_ddc.c
> index 267180e7bc48..5d2bcce2f669 100644
> --- a/drivers/gpu/drm/amd/display/dc/link/protocols/link_ddc.c
> +++ b/drivers/gpu/drm/amd/display/dc/link/protocols/link_ddc.c
> @@ -549,7 +549,8 @@ void write_scdc_data(struct ddc_service *ddc_service,
>      /*Lower than 340 Scramble bit from SCDC caps*/
> 
>      if (ddc_service->link->local_sink &&
> -        ddc_service->link->local_sink->edid_caps.panel_patch.skip_scdc_overwrite)
> +        (ddc_service->link->local_sink->edid_caps.panel_patch.skip_scdc_overwrite
> ||
> +        !ddc_service->link->local_sink->edid_caps.scdc_present))
>          return;
> 
>      link_query_ddc_data(ddc_service, slave_address, &offset,
> 
> 
> It appears that scdc_present is always false on my device.
> I reverted the change to write_scdc_data(), and the monitor works
> normally at high refresh rates.

Can you cc: the developers and maintainers of this change to let them
know?  Otherwise they will not notice it.  Also, does 7.0-rc2 show this
issue?

thanks,

greg k-h

Re: [BUG] HDMI monitor shows no signal when the refresh rate is higher than the default 60Hz

[hgfdgjn]

7.0-rc2 can also reproduce it; after locating the issue, it was
reproduced using the stable upstream master branch.


>
> On Sun, Mar 08, 2026 at 05:42:39PM +0800, hgfdgjn wrote:
> > Hi maintainers:
> >
> >   After updating to v6.19.6 on Arch Linux, if I set the refresh rate
> > higher than 60Hz, the monitor displays "No Signal".
> > I tried bisecting and found:
> > > # first bad commit: [3471b9a31ce352ffb343cf02a991261880aac3a7] drm/amd/display: Rework HDMI data channel reads
> >
> > This issue on my machine was caused by this change:
> >
> > diff --git a/drivers/gpu/drm/amd/display/dc/link/protocols/link_ddc.c
> > b/drivers/gpu/drm/amd/display/dc/link/protocols/link_ddc.c
> > index 267180e7bc48..5d2bcce2f669 100644
> > --- a/drivers/gpu/drm/amd/display/dc/link/protocols/link_ddc.c
> > +++ b/drivers/gpu/drm/amd/display/dc/link/protocols/link_ddc.c
> > @@ -549,7 +549,8 @@ void write_scdc_data(struct ddc_service *ddc_service,
> >      /*Lower than 340 Scramble bit from SCDC caps*/
> >
> >      if (ddc_service->link->local_sink &&
> > -        ddc_service->link->local_sink->edid_caps.panel_patch.skip_scdc_overwrite)
> > +        (ddc_service->link->local_sink->edid_caps.panel_patch.skip_scdc_overwrite
> > ||
> > +        !ddc_service->link->local_sink->edid_caps.scdc_present))
> >          return;
> >
> >      link_query_ddc_data(ddc_service, slave_address, &offset,
> >
> >
> > It appears that scdc_present is always false on my device.
> > I reverted the change to write_scdc_data(), and the monitor works
> > normally at high refresh rates.
>
> Can you cc: the developers and maintainers of this change to let them
> know?  Otherwise they will not notice it.  Also, does 7.0-rc2 show this
> issue?
>
> thanks,
>
> greg k-h