Re: [PATCH v5 05/10] drm/bridge: dw-hdmi-qp: Add HDMI 2.0 SCDC scrambling and high TMDS clock ratio support

Dmitry Baryshkov
2026-05-05T00:45:09Z

On Tue, Apr 28, 2026 at 04:51:46PM +0300, Cristian Ciocaltea wrote:
> Hi Dmitry,
>
> Thanks for taking the time to review the series!
>
> On 4/28/26 4:38 AM, Dmitry Baryshkov wrote:
> > On Sun, Apr 26, 2026 at 03:20:17AM +0300, Cristian Ciocaltea wrote:
> >> Enable HDMI 2.0 display modes (e.g. 4K@60Hz) by adding SCDC management
> >> for the high TMDS clock ratio and scrambling, required when the TMDS
> >> character rate exceeds the 340 MHz HDMI 1.4b limit.
> >>
> >> A periodic work item monitors the sink's scrambling status to recover
> >> from sink-side resets. On hotplug detect, if SCDC scrambling state is
> >> out of sync with the driver, trigger a CRTC reset to re-establish the
> >> link.
> >>
> >> Reject modes requiring TMDS rates above 600 MHz, as those fall in the
> >> HDMI 2.1 FRL domain which is not supported. In no_hpd configurations,
> >> further restrict to 340 MHz since SCDC requires a connected sink.
> >>
> >> Tested-by: Diederik de Haas <diederik@cknow-tech.com>
> >> Tested-by: Maud Spierings <maud_spierings@hotmail.com>
> >> Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
> >> ---
> >> drivers/gpu/drm/bridge/synopsys/dw-hdmi-qp.c | 188 ++++++++++++++++++++++++---
> >> 1 file changed, 172 insertions(+), 16 deletions(-)
> >
> > My main issue with this patch (sorry) is that this adds yet another copy
> > of SCDC-related helpers into the driver which already OP_HDMI and other
> > helpers.
> >

>
> >> +
> >> + drm_atomic_helper_connector_hdmi_hotplug(connector,
> >> + connector_status_connected);
> >
> > I don't see a forced hotplug event in the existing drivers. Why is it
> > necessary? This function is being called from the detect() path.
>
> For some reason, without it, the connector seems to lose its state after reset:
>
> [ 2142.982967] dwhdmiqp-rockchip fde80000.hdmi: resetting crtc
> [ 2142.994132] rockchip-drm display-subsystem: [drm] HDMI Sink doesn't support RGB, something's wrong.
> [ 2143.140827] dwhdmiqp-rockchip fde80000.hdmi: dw_hdmi_qp_bridge_atomic_enable mode=DVI
>
> Will recheck if that's still the case after the HPD handling rework.

I think so. If it doesn't help, please check that
drm_bridge_connector_detect() is called for each hotplug event from the
hardware. It should take care of parsing EDID (and thus updating HDMI
Sink properties).

--
With best wishes
Dmitry