Re: [PATCH v8 04/39] drm/connector: Add HDMI 2.0 scrambler infrastructure

[Dmitry Baryshkov]

On Thu, Jul 16, 2026 at 03:50:29PM +0200, Maxime Ripard wrote:
> On Wed, Jul 15, 2026 at 01:46:12PM +0300, Cristian Ciocaltea wrote:
> > On 7/15/26 11:55 AM, Maxime Ripard wrote:
> > > On Mon, Jul 13, 2026 at 01:23:00PM +0300, Cristian Ciocaltea wrote:
> > >> On 7/13/26 11:50 AM, Maxime Ripard wrote:
> > >>> On Thu, Jul 09, 2026 at 10:25:54PM +0300, Cristian Ciocaltea wrote:
> > >>>> On 7/3/26 11:54 PM, Cristian Ciocaltea wrote:
> > >>>>> On 7/3/26 5:34 PM, Dmitry Baryshkov wrote:
> > >>>>>> On Thu, Jul 02, 2026 at 05:46:17PM +0300, Cristian Ciocaltea wrote:
> > >>>>>>> Add the connector-level infrastructure to support HDMI 2.0 scrambling:
> > >>>>>>>
> > >>>>>>> - A scrambler_supported flag to indicate whether the source supports the
> > >>>>>>>   scrambling capability, in which case the newly introduced
> > >>>>>>>   .scrambler_{enable|disable}() callbacks in drm_connector_hdmi_funcs
> > >>>>>>>   are mandatory
> > >>>>>>
> > >>>>>> Do we need a flag? What would it mean if the flag is set, but the
> > >>>>>> callbacks are not? Can we drop the flag and use the presence of the
> > >>>>>> callbacks as a way to identify that scrambler is enabled?
> > >>>>>
> > >>>>> The flag is intended to be set only within drmm_connector_hdmi_init_with_caps()
> > >>>>> when drivers advertise HDMI 2.x capability, in which case it also ensures the
> > >>>>> callbacks are provided.  
> > >>>>>
> > >>>>> We could drop the flag and instead have the init helper clear the callbacks if
> > >>>>> they were provided for HDMI 1.x.  This might slightly reduce code readability,
> > >>>>> as it relies on checking the presence of individual callbacks - especially since
> > >>>>> we plan to extend this further with HDMI 2.1 support, providing four or five
> > >>>>> additional FRL-specific callbacks.
> > >>>>
> > >>>> I tried to replace the flag with a helper that checks the presence of (one of)
> > >>>> the callbacks, but it's not straightforward to unset those for non-HDMI 2.x
> > >>>> cases since the hdmi_funcs argument is immutable.
> > >>>
> > >>> I'm not sure why we would need to unset them. If the driver states that
> > >>> it support HDMI 2.0, then it needs to be there, if it doesn't, then who
> > >>> cares? it's not going to be used. We can log a warning that it's
> > >>> inconsistent I guess, but there's no need to actively remove it.
> > >>
> > >> I was trying to address the use case where drivers provide the scrambler
> > >> callbacks despite not supporting HDMI 2.0.
> > > 
> > > Scrambling got introduced with HDMI 2.0. That doesn't make sense, but
> > > it's not a total deal breaker, it's just going to be here unused. Hence
> > > why I was suggesting to put a warning there if you wanted to.
> > > 
> > >> If we replace the scrambler_supported flag with a helper checking the
> > >> presence of the scrambler callbacks, then we would need to ensure the
> > >> callbacks do not exist in this case.
> > > 
> > > Keep it simple:
> > > 
> > > if (hdmi_version >= HDMI_VERSION_2_0)
> > >    if (funcs->scrambler_enable)
> > >       hdmi->scramblers_supported = true
> > >    else
> > >       return -EINVAL
> > > else
> > >     drm_warn(warn, "Inconsistent HDMI version");
> > > 
> > > We don't need anything more than that.
> > 
> > I dropped the scrambler_supported flag and introduced a helper:
> > 
> > static inline bool
> > drm_connector_hdmi_scrambler_supported(struct drm_connector *connector)
> > {
> > 	return connector->hdmi.funcs && connector->hdmi.funcs->scrambler_enable;
> 
> I'd add disable to that test

I'd make it an error, if there is only scrambler_enable without
scrambler_disable (or vice versa).

> 
> > }
> > 
> > Therefore we need to ensure the callbacks are not set in the HDMI 1.x cases:
> > 
> > int drmm_connector_hdmi_init_with_caps()
> > {
> > 	...
> > 	if (caps->supported_hdmi_ver >= HDMI_VERSION_2_0) {
> > 		if (!hdmi_funcs->scrambler_enable ||
> > 		    !hdmi_funcs->scrambler_disable)
> > 			return -EINVAL;
> > 
> > 		connector->hdmi.max_tmds_char_rate = HDMI_2_0_TMDS_CHAR_RATE_MAX_HZ;
> > 	} else {
> > 		/*
> > 		 * Scrambler callbacks are only valid for connectors advertising
> > 		 * HDMI 2.0 capability. drm_connector_hdmi_scrambler_supported()
> > 		 * relies on their presence to report scrambling support.
> > 		 */
> > 		if (hdmi_funcs->scrambler_enable ||
> > 		    hdmi_funcs->scrambler_disable)
> > 			return -EINVAL;
> > 
> > 		if (caps->supported_hdmi_ver >= HDMI_VERSION_1_3) {
> > 			connector->hdmi.max_tmds_char_rate = HDMI_1_3_TMDS_CHAR_RATE_MAX_HZ;
> > 		} else if (caps->supported_hdmi_ver >= HDMI_VERSION_1_0) {
> > 			connector->hdmi.max_tmds_char_rate = HDMI_1_0_TMDS_CHAR_RATE_MAX_HZ;
> > 		}
> > 	}
> 
> Drivers might have a lower limit than the max allowed by the spec. It
> should be provided by the driver, possibly optionally with a fallback to
> what the spec states?

Yes, likely it can be handled with the if !connector->hdmi.max_tmds_char_rate.

-- 
With best wishes
Dmitry