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

On 04-10-26, 00:33, Cristian Ciocaltea wrote:

Hi Vinod,

On 10/3/26 11:39 PM, Vinod Koul wrote:

quoted

On 01-09-26, 22:55, Cristian Ciocaltea wrote:

quoted

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. 

Ah, looks like AI gave me wrong info about 0 being invalid, this is okay
then


-- 
~Vinod