[PATCH net-next v3 2/4] net: mdio: add PTP offset compensation to mdiobus_write_sts
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STALE2622d
From: Hubert Feurstein <hidden>
Date: 2019-08-20 08:49:07
Also in:
lkml
Subsystem:
ethernet phy library, networking drivers, the rest · Maintainers:
Andrew Lunn, Heiner Kallweit, Andrew Lunn, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds
Revision v3 (3 revisions archived).
Revisions (3)
- v1
- v2 [diff against previous]
- v3 current [diff against previous]
From: Hubert Feurstein <redacted> The slow MDIO access introduces quite a big offset (~13us) to the PTP system time synchronisation. With this patch the driver has the possibility to set the correct offset which can then be compensated. Signed-off-by: Hubert Feurstein <redacted> --- drivers/net/phy/mdio_bus.c | 12 ++++++++++++ include/linux/phy.h | 8 ++++++++ 2 files changed, 20 insertions(+)
diff --git a/drivers/net/phy/mdio_bus.c b/drivers/net/phy/mdio_bus.c
index 4dba2714495e..50a37cf46f96 100644
--- a/drivers/net/phy/mdio_bus.c
+++ b/drivers/net/phy/mdio_bus.c@@ -739,6 +739,18 @@ int __mdiobus_write_sts(struct mii_bus *bus, int addr, u32 regnum, u16 val, if (!(bus->flags & MII_BUS_F_PTP_STS_SUPPORTED)) ptp_read_system_postts(sts); + /* PTP offset compensation: + * After the MDIO access is completed (from the chip perspective), the + * switch chip will snapshot the PHC timestamp. To make sure our system + * timestamp corresponds to the PHC timestamp, we have to add the + * duration of this MDIO access to sts->post_ts. Linuxptp's phc2sys + * takes the average of pre_ts and post_ts to calculate the final + * system timestamp. With this in mind, we have to add ptp_sts_offset + * twice to post_ts, in order to not introduce an constant time offset. + */ + if (sts) + timespec64_add_ns(&sts->post_ts, 2 * bus->ptp_sts_offset); + return retval; } EXPORT_SYMBOL(__mdiobus_write_sts);
diff --git a/include/linux/phy.h b/include/linux/phy.h
index 0b33662e0320..615df9c7f2c3 100644
--- a/include/linux/phy.h
+++ b/include/linux/phy.h@@ -283,8 +283,16 @@ struct mii_bus { * The ptp_read_system_*ts functions already check the ptp_sts pointer. * The MII_BUS_F_PTP_STS_SUPPORTED-bit must be set in flags, when the * MDIO bus driver takes the timestamps as described above. + * + * @ptp_sts_offset: This is the compensation offset for the system + * timestamp which is introduced by the slow MDIO access duration. An + * MDIO access consists of 32 clock cycles. Usually the MDIO bus runs + * at ~2.5MHz, so we have to compensate ~12800ns offset. + * Set the ptp_sts_offset to the exact duration of one MDIO frame + * (= 32 * clock-period) in nano-seconds. */ struct ptp_system_timestamp *ptp_sts; + u32 ptp_sts_offset; }; #define to_mii_bus(d) container_of(d, struct mii_bus, dev)
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2.22.1