[PATCH 1/2] phy: hdmi: Add optional FRL TxFFE config options

[Cristian Ciocaltea]

During HDMI 2.1 FRL link training, the source and sink can negotiate a
Transmitter Feed Forward Equalizer (TxFFE) level to compensate for
signal quality degradation.  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.

It's worth noting 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 flag-based approach reflects an important invariant in the link
training process: whenever the FRL rate or lane count changes, the TxFFE
level must be reset to zero.  A separate phy_configure() call with
set_ffe_level can only follow after the rate has been established,
making the two operations deliberately distinct.

Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@xxxxxxxxxxxxx>
---
 include/linux/phy/phy-hdmi.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/include/linux/phy/phy-hdmi.h b/include/linux/phy/phy-hdmi.h
index d4cf4430ee8f..1d4b62475079 100644
--- a/include/linux/phy/phy-hdmi.h
+++ b/include/linux/phy/phy-hdmi.h
@@ -19,6 +19,10 @@ enum phy_hdmi_mode {
  * @tmds_char_rate: HDMI TMDS Character Rate in Hertz.
  * @frl.rate_per_lane: HDMI FRL Rate per Lane in Gbps.
  * @frl.lanes: HDMI FRL lanes count.
+ * @frl.ffe_level: Transmitter Feed Forward Equalizer Level.
+ *	Optional, only meaningful when set_ffe_level flag is on.
+ * @frl.set_ffe_level: Flag indicating whether or not to reconfigure ffe_level.
+ *	All the other struct fields must be ignored when this is used.
  *
  * This structure is used to represent the configuration state of a HDMI phy.
  */
@@ -29,6 +33,8 @@ struct phy_configure_opts_hdmi {
 		struct {
 			u8 rate_per_lane;
 			u8 lanes;
+			u8 ffe_level;
+			u8 set_ffe_level : 1;
 		} frl;
 	};
 };

-- 
2.52.0