Re: [PATCH v2 1/3] phy: hdmi: Add optional FRL TxFFE config options

[Cristian Ciocaltea <cristian.ciocaltea@collabora.com>]

Hi Vinod,

On 10/3/26 11:39 PM, Vinod Koul wrote:
> On 01-09-26, 22:55, Cristian Ciocaltea wrote:
>> During HDMI 2.1 FRL link training, the source and sink can negotiate a
>> Transmitter Feed-Forward Equalization (TxFFE) level to improve the
>> signal quality.  Starting from zero, the source may increment the TxFFE
>> level up to a maximum agreed during the LTS3 stage if the sink keeps
>> reporting FLT failures.  TxFFE adjustment is optional and only attempted
>> when both the source and the connected sink support it.
>>
>> Since the existing HDMI PHY configuration API covers the FRL rate/lane
>> selection only, provide the following fields to the frl sub-struct of
>> phy_configure_opts_hdmi:
>>
>> * ffe_level: the TxFFE level to apply, only meaningful when
>>   set_ffe_level is set.
>>
>> * set_ffe_level: a 1-bit flag that changes the semantics of the
>>   phy_configure() call, i.e. when set, the PHY driver must apply the new
>>   ffe_level and ignore the other frl related fields.
> 
> The ffe_level 0 implies it is disabled, so why should we use a flag for
> this? Rather use if value valid (non zero) logic to apply..?

That's not quite possible because level 0 is valid (and the default) according
to HDMI 2.1 spec. The source is expected to reset TxFFE to default whenever a
new FRL rate is set, hence the API shall be conformant. 

Regards,
Cristian