Re: [PATCH v2] drm/i915/hdmi: Poll for 200 msec for TMDS_Scrambler_Status

["Murthy, Arun R" <arun.r.murthy@intel.com>]

On 01-04-2026 18:30, Nautiyal, Ankit K wrote:
>
> On 4/1/2026 3:11 PM, Murthy, Arun R wrote:
>>
>>> -----Original Message-----
>>> From: Intel-gfx <intel-gfx-bounces@lists.freedesktop.org> On Behalf 
>>> Of Jérôme
>>> Tollet
>>> Sent: Thursday, January 8, 2026 2:38 PM
>>> To: Jani Nikula <jani.nikula@linux.intel.com>; Vivi, Rodrigo
>>> <rodrigo.vivi@intel.com>; Nautiyal, Ankit K 
>>> <ankit.k.nautiyal@intel.com>
>>> Cc: intel-gfx@lists.freedesktop.org; intel-xe@lists.freedesktop.org
>>> Subject: [PATCH v2] drm/i915/hdmi: Poll for 200 msec for
>>> TMDS_Scrambler_Status
>>>
>>> Hello,
>>> As per HDMI 2.0 specification, after scrambled video transmission 
>>> begins,  the
>>> source must poll the TMDS_Scrambler_Status bit until it reads 1 or  
>>> until a
>>> timeout of 200 ms.
>>>
>>>   Add a polling step after enabling the HDMI port to verify 
>>> scrambling  status,
>>> following the spec requirement.
>>>
>>>   Without the wait for the scrambling bit to set, some HDMI 2.0 
>>> monitors fail  to
>>> decode the signal at 4K@60Hz (594 MHz) when SCDC scrambling is not yet
>>> fully configured by the sink.
>>>
>>>   v2:
>>>    - Instead of the fixed delay, poll for TMDS scramble status for 
>>> 200 msec
>>>      as per the HDMI spec. (Ankit)
>>>
>>>   Reported-by: Jerome Tollet <jerome.tollet@gmail.com>
>>>   Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/6868
>>>   Link: https://lore.kernel.org/dri-devel/20251230091037.5603-1-
>>> jerome.tollet@gmail.com/
>>>   Signed-off-by: Jerome Tollet <jerome.tollet@gmail.com>
>>>   Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
>>>   ---
>>>    drivers/gpu/drm/i915/display/intel_ddi.c  |  2 ++
>>>    drivers/gpu/drm/i915/display/intel_hdmi.c | 25 
>>> +++++++++++++++++++++++
>>>    drivers/gpu/drm/i915/display/intel_hdmi.h |  2 ++
>>>    3 files changed, 29 insertions(+)
>>>
>>>   diff --git a/drivers/gpu/drm/i915/display/intel_ddi.c
>>> b/drivers/gpu/drm/i915/display/intel_ddi.c
>>>   index cb91d07cdaa6..c708b713f0e8 100644
>>>   --- a/drivers/gpu/drm/i915/display/intel_ddi.c
>>>   +++ b/drivers/gpu/drm/i915/display/intel_ddi.c
>>>   @@ -3506,6 +3506,8 @@ static void intel_ddi_enable_hdmi(struct
>>> intel_atomic_state *state,
>>>    }
>>>
>>>    intel_ddi_buf_enable(encoder, buf_ctl);  +  +
>>> intel_hdmi_poll_for_scrambling_enable(crtc_state, connector);
>>>    }
>>>
>>>    static void intel_ddi_enable(struct intel_atomic_state *state,  
>>> diff --git
>>> a/drivers/gpu/drm/i915/display/intel_hdmi.c
>>> b/drivers/gpu/drm/i915/display/intel_hdmi.c
>>>   index 055e68810d0d..958d939ae6ee 100644
>>>   --- a/drivers/gpu/drm/i915/display/intel_hdmi.c
>>>   +++ b/drivers/gpu/drm/i915/display/intel_hdmi.c
>>>   @@ -2694,6 +2694,31 @@ intel_hdmi_add_properties(struct intel_hdmi
>>> *intel_hdmi, struct drm_connector *_
>>> drm_connector_attach_max_bpc_property(&connector->base, 8, 12);
>>>    }
>>>
>>>   +/*
>>>   + * As Per HDMI 2.0 spec: after scrambled video transmission 
>>> begins,  + * poll
>>> TMDS_Scrambler_Status until it reads 1, for up to 200 ms.
>>>   + */
>> Can you point out to the section in the spec?
>
> HDMI Specification 2.0
>
> Section 6.1.3 Control
>
> Subsection 6.1.3.1 Scrambling Control
>
> Mentions about the polling for TMDS_Scrambler_bit for 200msec.
>
>
Please add this sec and sub-sec details in the comments.
Upon adding this

Reviewed-by: Arun R Murthy <arun.r.murthy@intel.com>


Thanks and Regards,
Arun R Murthy
--------------------