[RFC PATCH v2 net-next 02/15] phy: introduce the PHY_MODE_ETHTOOL mode for phy_set_mode_ext()

[Vladimir Oltean]

In networking, we have 2 distinct data types:

- phy_interface_t describes the link between a MAC (or MAC-side PCS) and
  an attached PHY or SFP cage

- enum ethtool_link_mode_bit_indices describes the link between a local
  PHY and a remote PHY (for example, gigabit RJ45 twisted copper pairs)

Currently, phy_set_mode_ext(PHY_MODE_ETHERNET) takes arguments of the
phy_interface_t type, and there is no way to pass an argument of the
enum ethtool_link_mode_bit_indices type. The new PHY_MODE_ETHTOOL
intends to address that.

It is true that there is currently some overlap between these data
types, namely:

 phy_interface_t                enum ethtool_link_mode_bit_indices
 -----------------------------------------------------------------
 PHY_INTERFACE_MODE_10GKR       ETHTOOL_LINK_MODE_10000baseKR_Full_BIT
 PHY_INTERFACE_MODE_1000BASEKX  ETHTOOL_LINK_MODE_1000baseKX_Full_BIT

but those overlaps were deemed to be mistakes, and PHY-to-PHY link modes
should only be added to ethtool_link_mode_bit_indices going forward.
Thus, I believe that the distinction is necessary, rather than hacking
more improper PHY modes. Some of the PHY-to-PHY link modes which may be
added in the future (to ethtool_link_mode_bit_indices and not to
phy_interface_t) are:

	ETHTOOL_LINK_MODE_100000baseKP4_Full_BIT
	ETHTOOL_LINK_MODE_100000baseCR10_Full_BIT
	ETHTOOL_LINK_MODE_25000baseKR_S_Full_BIT
	ETHTOOL_LINK_MODE_25000baseCR_S_Full_BIT

One user of PHY_MODE_ETHTOOL will be the MTIP backplane AN/LT + Lynx
SerDes PHY combo, where the backplane autoneg protocol (IEEE 802.3
clause 73) selects the operating PHY-to-PHY link mode.

There are electrical differences between the PHY-to-PHY backplane link
modes (like ETHTOOL_LINK_MODE_10000baseKR_Full_BIT) and their
non-backplane counterparts (like PHY_INTERFACE_MODE_10GBASER), namely
the number of TX signal equalization taps and their configurability.
This further justifies distinguishing between them in the generic PHY
API.

Signed-off-by: Vladimir Oltean <vladimir.oltean@xxxxxxx>
---
v1->v2: rename PHY_MODE_ETHERNET_PHY to PHY_MODE_ETHTOOL at Russell's
suggestion

 include/linux/phy/phy.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/linux/phy/phy.h b/include/linux/phy/phy.h
index 6be348f1fa0e..72ef4afcda81 100644
--- a/include/linux/phy/phy.h
+++ b/include/linux/phy/phy.h
@@ -39,6 +39,7 @@ enum phy_mode {
 	PHY_MODE_UFS_HS_B,
 	PHY_MODE_PCIE,
 	PHY_MODE_ETHERNET,
+	PHY_MODE_ETHTOOL,
 	PHY_MODE_MIPI_DPHY,
 	PHY_MODE_SATA,
 	PHY_MODE_LVDS,
@@ -52,7 +53,7 @@ enum phy_media {
 };
 
 enum phy_status_type {
-	/* Valid for PHY_MODE_ETHERNET */
+	/* Valid for PHY_MODE_ETHERNET and PHY_MODE_ETHTOOL */
 	PHY_STATUS_CDR_LOCK,
 };
 
-- 
2.34.1