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

[Cristian Ciocaltea]

On 7/22/26 9:51 AM, Dmitry Baryshkov wrote:
> 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).

hdmi_init() already guaranties that both scrambler callbacks must be present
when supported_hdmi_ver indicates HDMI_VERSION_2_0, and neither of them
otherwise.

Regardless, I've already added scrambler_disable to the check above to improve
code readability.

Thanks,
Cristian