[PATCH net-next 2/5] net: phy: broadcom: use timestamped MDIO writes in gettimex64

[James Clark <jjc@jclark.com>]

Use __phy_write_sts() to obtain tighter system timestamp bounds in
gettimex64 by timestamping completion of the write that triggers
capture of the PHC time.

The PHY captures its time a short delay after the end of the write.
End-to-end measurements show that the delay is small, within the
measurement accuracy of a few tenths of a microsecond.

This patch does not try to fix the error handling in the existing
framesync code, which ignores MDIO write errors.

Signed-off-by: James Clark <jjc@jclark.com>
Assisted-by: LLM
---
Does Broadcom know the delay from the end of the MDIO write to the
framesync capture in the BCM54210PE? If so, I can add compensation
for it.

 drivers/net/phy/bcm-phy-lib.c | 25 +++++++++++++++++++++++++
 drivers/net/phy/bcm-phy-lib.h |  7 +++++++
 drivers/net/phy/bcm-phy-ptp.c | 27 +++++++++++++++++++++------
 3 files changed, 53 insertions(+), 6 deletions(-)

diff --git a/drivers/net/phy/bcm-phy-lib.c b/drivers/net/phy/bcm-phy-lib.c
index b64beade8dd..022f5e5e6ce 100644
--- a/drivers/net/phy/bcm-phy-lib.c
+++ b/drivers/net/phy/bcm-phy-lib.c
@@ -42,6 +42,31 @@ int bcm_phy_write_exp(struct phy_device *phydev, u16 reg, u16 val)
 }
 EXPORT_SYMBOL_GPL(bcm_phy_write_exp);
 
+static int __bcm_phy_write_exp_sts(struct phy_device *phydev, u16 reg, u16 val,
+				   struct ptp_system_timestamp *sts)
+{
+	int rc;
+
+	rc = __phy_write(phydev, MII_BCM54XX_EXP_SEL, reg);
+	if (rc < 0)
+		return rc;
+
+	return __phy_write_sts(phydev, MII_BCM54XX_EXP_DATA, val, sts);
+}
+
+int bcm_phy_write_exp_sts(struct phy_device *phydev, u16 reg, u16 val,
+			  struct ptp_system_timestamp *sts)
+{
+	int rc;
+
+	phy_lock_mdio_bus(phydev);
+	rc = __bcm_phy_write_exp_sts(phydev, reg, val, sts);
+	phy_unlock_mdio_bus(phydev);
+
+	return rc;
+}
+EXPORT_SYMBOL_GPL(bcm_phy_write_exp_sts);
+
 int __bcm_phy_read_exp(struct phy_device *phydev, u16 reg)
 {
 	int val;
diff --git a/drivers/net/phy/bcm-phy-lib.h b/drivers/net/phy/bcm-phy-lib.h
index bba94ce9619..365cb3d1c32 100644
--- a/drivers/net/phy/bcm-phy-lib.h
+++ b/drivers/net/phy/bcm-phy-lib.h
@@ -34,6 +34,8 @@ int __bcm_phy_write_exp(struct phy_device *phydev, u16 reg, u16 val);
 int __bcm_phy_read_exp(struct phy_device *phydev, u16 reg);
 int __bcm_phy_modify_exp(struct phy_device *phydev, u16 reg, u16 mask, u16 set);
 int bcm_phy_write_exp(struct phy_device *phydev, u16 reg, u16 val);
+int bcm_phy_write_exp_sts(struct phy_device *phydev, u16 reg, u16 val,
+			  struct ptp_system_timestamp *sts);
 int bcm_phy_read_exp(struct phy_device *phydev, u16 reg);
 int bcm_phy_modify_exp(struct phy_device *phydev, u16 reg, u16 mask, u16 set);
 
@@ -48,6 +50,11 @@ static inline int bcm_phy_read_exp_sel(struct phy_device *phydev, u16 reg)
 	return bcm_phy_read_exp(phydev, reg | MII_BCM54XX_EXP_SEL_ER);
 }
 
+static inline bool bcm_phy_supports_write_exp_sts(struct phy_device *phydev)
+{
+	return phy_supports_write_sts(phydev);
+}
+
 int bcm54xx_auxctl_write(struct phy_device *phydev, u16 regnum, u16 val);
 int bcm54xx_auxctl_read(struct phy_device *phydev, u16 regnum);
 
diff --git a/drivers/net/phy/bcm-phy-ptp.c b/drivers/net/phy/bcm-phy-ptp.c
index 65d609ed69f..2d8b377010b 100644
--- a/drivers/net/phy/bcm-phy-ptp.c
+++ b/drivers/net/phy/bcm-phy-ptp.c
@@ -214,22 +214,34 @@ static void bcm_ptp_framesync(struct phy_device *phydev, u16 ctrl)
 	bcm_phy_write_exp(phydev, NSE_CTRL, ctrl | NSE_CPU_FRAMESYNC);
 }
 
+static int bcm_ptp_framesync_sts(struct phy_device *phydev, u16 ctrl,
+				 struct ptp_system_timestamp *sts)
+{
+	return bcm_phy_write_exp_sts(phydev, NSE_CTRL,
+				     ctrl | NSE_CPU_FRAMESYNC, sts);
+}
+
 static int bcm_ptp_framesync_ts(struct phy_device *phydev,
 				struct ptp_system_timestamp *sts,
 				struct timespec64 *ts,
 				u16 orig_ctrl)
 {
 	u16 ctrl, reg;
-	int i;
+	int i, err = 0;
 
 	ctrl = bcm_ptp_framesync_disable(phydev, orig_ctrl);
 
-	ptp_read_system_prets(sts);
-
 	/* trigger framesync + capture */
-	bcm_ptp_framesync(phydev, ctrl | NSE_CAPTURE_EN);
-
-	ptp_read_system_postts(sts);
+	if (sts && bcm_phy_supports_write_exp_sts(phydev)) {
+		/* cannot ignore error since sts may be uninitialized,
+		 * but still poll for any triggered capture
+		 */
+		err = bcm_ptp_framesync_sts(phydev, ctrl | NSE_CAPTURE_EN, sts);
+	} else {
+		ptp_read_system_prets(sts);
+		bcm_ptp_framesync(phydev, ctrl | NSE_CAPTURE_EN);
+		ptp_read_system_postts(sts);
+	}
 
 	/* poll for FSYNC interrupt from TS capture */
 	for (i = 0; i < 10; i++) {
@@ -242,6 +254,9 @@ static int bcm_ptp_framesync_ts(struct phy_device *phydev,
 
 	bcm_ptp_framesync_restore(phydev, orig_ctrl);
 
+	if (err)
+		return err;
+
 	return reg & INTC_FSYNC ? 0 : -ETIMEDOUT;
 }
 
-- 
2.56.0