[PATCH] net: ti: am65-cpsw-nuss: allow skipping phy_config() for speed

[Siddharth Vadapalli]

Currently, phy_config() is invoked every time during am65_cpsw_start()
which guarantees robustness and also allows recovering from link
failures by resetting the Ethernet PHY. While this is beneficial for
system stability, for use-cases where speed is prioritized over
robustness, the existing implementation is insufficient.

To support use-cases prioritizing speed while continuing to retain the
existing behavior for robustness, sample the environment variable named
"am65_cpsw_phy_config_once" to determine whether phy_config() should
continue to be invoked once per invocation of am65_cpsw_start(), OR, it
should only be invoked across invocations. Since the environment variable
is not set by default, robustness is prioritized over speed. Use-cases
which require speed can set "am65_cpsw_phy_config_once" to any of:
'1', 'y', 'Y', 't' and 'T'
based on the implementation of the env_get_yesno() helper function.

Signed-off-by: Siddharth Vadapalli <s-vadapalli at ti.com>
---

Hello,

This patch is based on commit
3cdce049f90 erge tag 'u-boot-rockchip-20260610' of https://source.denx.de/u-boot/custodians/u-boot-rockchip
of the master branch of U-Boot.

Patch has been tested on J784S4 EVM which uses MCU CPSW2G for Ethernet
functionality. The following test logs demonstrate the default behavior
being retained in the absence of 'am65_cpsw_phy_config_once' environment
variable being set to a logical true, followed by setting the environment
variable to a logical true ('y') and observing the PHY Autonegotiation
process being skipped, followed by setting the environment variable to a
logical false ('n' but could be anything that isn't logically true based
on the env_get_yesno() helper function) and verifying that we go back to
the default behavior of performing PHY Autonegotiation again:
https://gist.github.com/Siddharth-Vadapalli-at-TI/6229b5a3b7d80cd0c2037a6364406bbe

Regards,
Siddharth.

 drivers/net/ti/am65-cpsw-nuss.c | 32 +++++++++++++++++++++++++++-----
 1 file changed, 27 insertions(+), 5 deletions(-)

diff --git a/drivers/net/ti/am65-cpsw-nuss.c b/drivers/net/ti/am65-cpsw-nuss.c
index 84a3e44ecbc..a5cca52f674 100644
--- a/drivers/net/ti/am65-cpsw-nuss.c
+++ b/drivers/net/ti/am65-cpsw-nuss.c
@@ -18,6 +18,7 @@
 #include <dm/pinctrl.h>
 #include <dma-uclass.h>
 #include <dm/of_access.h>
+#include <env.h>
 #include <miiphy.h>
 #include <net.h>
 #include <phy.h>
@@ -104,6 +105,7 @@ struct am65_cpsw_port {
 	fdt_addr_t	macsl_base;
 	bool		disabled;
 	u32		mac_control;
+	bool            phy_configured;
 };
 
 struct am65_cpsw_common {
@@ -313,7 +315,7 @@ static int am65_cpsw_start(struct udevice *dev)
 	struct am65_cpsw_port *port = &common->ports[priv->port_id];
 	struct am65_cpsw_port *port0 = &common->ports[0];
 	struct ti_udma_drv_chan_cfg_data *dma_rx_cfg_data;
-	int ret, i;
+	int ret, i, skip_phy_config_env;
 
 	if (common->started)
 		return 0;
@@ -426,10 +428,30 @@ static int am65_cpsw_start(struct udevice *dev)
 		       port->port_sgmii_base + AM65_CPSW_SGMII_CONTROL_REG);
 	}
 
-	ret = phy_config(priv->phydev);
-	if (ret < 0) {
-		dev_err(dev, "phy_config failed: %d", ret);
-		goto err_dis_rx;
+	/*
+	 * Invoking phy_config() every time that am65_cpsw_start() is executed will
+	 * make the link robust. However, it delays every networking command such as
+	 * 'dhcp' and 'tftp'. For use-cases that prioritize speed over robustness,
+	 * phy_config() should be invoked only once. To support both use-cases,
+	 * sample the environment variable 'am65_cpsw_phy_config_once' to switch
+	 * between:
+	 * a) Invoke phy_config() every time - Default behavior for robustness
+	 * b) Invoke phy_config() once per driver probe - User configurable behavior
+	 *    for speed.
+	 */
+	skip_phy_config_env = env_get_yesno("am65_cpsw_phy_config_once");
+
+	/* If environment variable is not defined, assume it to be false. */
+	if (skip_phy_config_env == -1)
+		skip_phy_config_env = 0;
+
+	if (!port->phy_configured || !skip_phy_config_env) {
+		ret = phy_config(priv->phydev);
+		if (ret < 0) {
+			dev_err(dev, "phy_config failed: %d", ret);
+			goto err_dis_rx;
+		}
+		port->phy_configured = true;
 	}
 
 	ret = phy_startup(priv->phydev);
-- 
2.51.1