Messages in this thread | | | Date | Mon, 19 Aug 2019 15:17:36 +0200 | From | Andrew Lunn <> | Subject | Re: [PATCH net-next 1/3] net: mdio: add support for passing a PTP system timestamp to the mii_bus driver |
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On Fri, Aug 16, 2019 at 06:31:55PM +0200, Hubert Feurstein wrote: > In order to improve the synchronisation precision of phc2sys (from > the linuxptp project) for devices like switches which are attached > to the MDIO bus, it is necessary the get the system timestamps as > close as possible to the access which causes the PTP timestamp > register to be snapshotted in the switch hardware. Usually this is > triggered by an MDIO write access, the snapshotted timestamp is then > transferred by several MDIO reads. > > This patch adds the required infrastructure to solve the problem described > above. > > Signed-off-by: Hubert Feurstein <h.feurstein@gmail.com> > --- > drivers/net/phy/mdio_bus.c | 105 +++++++++++++++++++++++++++++++++++++ > include/linux/mdio.h | 7 +++ > include/linux/phy.h | 25 +++++++++ > 3 files changed, 137 insertions(+) > > diff --git a/drivers/net/phy/mdio_bus.c b/drivers/net/phy/mdio_bus.c > index bd04fe762056..167a21f267fa 100644 > --- a/drivers/net/phy/mdio_bus.c > +++ b/drivers/net/phy/mdio_bus.c > @@ -34,6 +34,7 @@ > #include <linux/phy.h> > #include <linux/io.h> > #include <linux/uaccess.h> > +#include <linux/ptp_clock_kernel.h> > > #define CREATE_TRACE_POINTS > #include <trace/events/mdio.h> > @@ -697,6 +698,110 @@ int mdiobus_write(struct mii_bus *bus, int addr, u32 regnum, u16 val) > } > EXPORT_SYMBOL(mdiobus_write); > > +/** > + * __mdiobus_write_sts - Unlocked version of the mdiobus_write_sts function > + * @bus: the mii_bus struct > + * @addr: the phy address > + * @regnum: register number to write > + * @val: value to write to @regnum > + * @sts: the ptp system timestamp > + * > + * Write a MDIO bus register and request the MDIO bus driver to take the > + * system timestamps when sts-pointer is valid. When the bus driver doesn't > + * support this, the timestamps are taken in this function instead. > + * > + * In order to improve the synchronisation precision of phc2sys (from > + * the linuxptp project) for devices like switches which are attached > + * to the MDIO bus, it is necessary the get the system timestamps as > + * close as possible to the access which causes the PTP timestamp > + * register to be snapshotted in the switch hardware. Usually this is > + * triggered by an MDIO write access, the snapshotted timestamp is then > + * transferred by several MDIO reads. > + * > + * Caller must hold the mdio bus lock. > + * > + * NOTE: MUST NOT be called from interrupt context. > + */ > +int __mdiobus_write_sts(struct mii_bus *bus, int addr, u32 regnum, u16 val, > + struct ptp_system_timestamp *sts) > +{ > + int retval; > + > + WARN_ON_ONCE(!mutex_is_locked(&bus->mdio_lock)); > + > + if (!bus->ptp_sts_supported) > + ptp_read_system_prets(sts);
How expensive is ptp_read_system_prets()? My original suggestion was to unconditionally call it here, and then let the driver overwrite it if it supports finer grained time stamping. MDIO is slow, so as long as ptp_read_system_prets() is not too expensive, i prefer KISS.
Andrew
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