The "phy-mode" property of devicetree indicates whether the PCB has
delay now, which means the mac needs to modify the PHY mode based
on whether there is an internal delay in the mac.

This modification is similar for many ethernet drivers. To simplify
code, define the helper phy_fix_phy_mode_for_mac_delays(speed, mac_txid,
mac_rxid) to fix PHY mode based on whether mac adds internal delay.

Signed-off-by: Inochi Amaoto <inochiama@gmail.com>
---
 drivers/net/phy/phy-core.c | 43 ++++++++++++++++++++++++++++++++++++++
 include/linux/phy.h        |  3 +++
 2 files changed, 46 insertions(+)

diff --git a/drivers/net/phy/phy-core.c b/drivers/net/phy/phy-core.c
index 605ca20ae192..4f258fb409da 100644
--- a/drivers/net/phy/phy-core.c
+++ b/drivers/net/phy/phy-core.c
@@ -101,6 +101,49 @@ const char *phy_rate_matching_to_str(int rate_matching)
 }
 EXPORT_SYMBOL_GPL(phy_rate_matching_to_str);

+/**
+ * phy_fix_phy_mode_for_mac_delays - Convenience function for fixing PHY
+ * mode based on whether mac adds internal delay
+ *
+ * @interface: The current interface mode of the port
+ * @mac_txid: True if the mac adds internal tx delay
+ * @mac_rxid: True if the mac adds internal rx delay
+ *
+ * Return fixed PHY mode, or PHY_INTERFACE_MODE_NA if the interface can
+ * not apply the internal delay
+ */
+phy_interface_t phy_fix_phy_mode_for_mac_delays(phy_interface_t interface,
+						bool mac_txid, bool mac_rxid)
+{
+	if (!phy_interface_mode_is_rgmii(interface))
+		return interface;
+
+	if (mac_txid && mac_rxid) {
+		if (interface == PHY_INTERFACE_MODE_RGMII_ID)
+			return PHY_INTERFACE_MODE_RGMII;
+		return PHY_INTERFACE_MODE_NA;
+	}
+
+	if (mac_txid) {
+		if (interface == PHY_INTERFACE_MODE_RGMII_ID)
+			return PHY_INTERFACE_MODE_RGMII_RXID;
+		if (interface == PHY_INTERFACE_MODE_RGMII_TXID)
+			return PHY_INTERFACE_MODE_RGMII;
+		return PHY_INTERFACE_MODE_NA;
+	}
+
+	if (mac_rxid) {
+		if (interface == PHY_INTERFACE_MODE_RGMII_ID)
+			return PHY_INTERFACE_MODE_RGMII_TXID;
+		if (interface == PHY_INTERFACE_MODE_RGMII_RXID)
+			return PHY_INTERFACE_MODE_RGMII;
+		return PHY_INTERFACE_MODE_NA;
+	}
+
+	return interface;
+}
+EXPORT_SYMBOL_GPL(phy_fix_phy_mode_for_mac_delays);
+
 /**
  * phy_interface_num_ports - Return the number of links that can be carried by
  *			     a given MAC-PHY physical link. Returns 0 if this is
diff --git a/include/linux/phy.h b/include/linux/phy.h
index 3c7634482356..0bc00a4cceb2 100644
--- a/include/linux/phy.h
+++ b/include/linux/phy.h
@@ -1813,6 +1813,9 @@ static inline bool phy_is_pseudo_fixed_link(struct phy_device *phydev)
 	return phydev->is_pseudo_fixed_link;
 }

+phy_interface_t phy_fix_phy_mode_for_mac_delays(phy_interface_t interface,
+						bool mac_txid, bool mac_rxid);
+
 int phy_save_page(struct phy_device *phydev);
 int phy_select_page(struct phy_device *phydev, int page);
 int phy_restore_page(struct phy_device *phydev, int oldpage, int ret);
--
2.51.1.dirty

On Mon, Oct 20, 2025 at 05:54:58PM +0800, Inochi Amaoto wrote:
> The "phy-mode" property of devicetree indicates whether the PCB has
> delay now, which means the mac needs to modify the PHY mode based
> on whether there is an internal delay in the mac.
> 
> This modification is similar for many ethernet drivers. To simplify
> code, define the helper phy_fix_phy_mode_for_mac_delays(speed, mac_txid,
> mac_rxid) to fix PHY mode based on whether mac adds internal delay.
> 
> Signed-off-by: Inochi Amaoto <inochiama@gmail.com>
> ---
>  drivers/net/phy/phy-core.c | 43 ++++++++++++++++++++++++++++++++++++++
>  include/linux/phy.h        |  3 +++
>  2 files changed, 46 insertions(+)
> 
> diff --git a/drivers/net/phy/phy-core.c b/drivers/net/phy/phy-core.c
> index 605ca20ae192..4f258fb409da 100644
> --- a/drivers/net/phy/phy-core.c
> +++ b/drivers/net/phy/phy-core.c
> @@ -101,6 +101,49 @@ const char *phy_rate_matching_to_str(int rate_matching)
>  }
>  EXPORT_SYMBOL_GPL(phy_rate_matching_to_str);
> 
> +/**
> + * phy_fix_phy_mode_for_mac_delays - Convenience function for fixing PHY
> + * mode based on whether mac adds internal delay
> + *
> + * @interface: The current interface mode of the port
> + * @mac_txid: True if the mac adds internal tx delay
> + * @mac_rxid: True if the mac adds internal rx delay
> + *
> + * Return fixed PHY mode, or PHY_INTERFACE_MODE_NA if the interface can
> + * not apply the internal delay
> + */

I think a helper like this is a good idea. But there are a couple of
things i don't like about this implementation.

I don't like returning PHY_INTERFACE_MODE_NA on error. I would prefer
-EINVAL.  of_get_phy_mode() passed a phy_interface_t *, and returns an
errno. The same would be good here.

I find:

phy_fix_phy_mode_for_mac_delays(interface, true, false)

hard to read. You cannot see what these true/false mean. Which is Rx
and which is Tx?

Rather than true false, how about passing an
PHY_INTERFACE_MODE_RGMII_* values?

PHY_INTERFACE_MODE_RGMII_ID would indicate the MAC is doing both
delays.  PHY_INTERFACE_MODE_RGMII_RXID the MAC is implementing the RX
delay? I'm open to other ideas here.

	Andrew