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Date: Tue, 26 May 2020 18:53:05 +0100 From: Russell King - ARM Linux admin <linux@...linux.org.uk> To: Jeremy Linton <jeremy.linton@....com> Cc: Andrew Lunn <andrew@...n.ch>, Heiner Kallweit <hkallweit1@...il.com>, Florian Fainelli <f.fainelli@...il.com>, netdev@...r.kernel.org Subject: Re: [PATCH RFC 4/7] net: phy: add support for probing MMDs >= 8 for devices-in-package On Tue, May 26, 2020 at 12:20:10PM -0500, Jeremy Linton wrote: > Hi, > > On 5/26/20 12:14 PM, Russell King - ARM Linux admin wrote: > > On Tue, May 26, 2020 at 03:31:16PM +0100, Russell King wrote: > > > Add support for probing MMDs above 7 for a valid devices-in-package > > > specifier. > > > > > > Signed-off-by: Russell King <rmk+kernel@...linux.org.uk> > > > --- > > > drivers/net/phy/phy_device.c | 39 ++++++++++++++++++++++++++++++++++-- > > > include/linux/phy.h | 2 ++ > > > 2 files changed, 39 insertions(+), 2 deletions(-) > > > > > > diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c > > > index 0d6b6ca66216..fa9164ac0f3d 100644 > > > --- a/drivers/net/phy/phy_device.c > > > +++ b/drivers/net/phy/phy_device.c > > > @@ -659,6 +659,28 @@ struct phy_device *phy_device_create(struct mii_bus *bus, int addr, u32 phy_id, > > > } > > > EXPORT_SYMBOL(phy_device_create); > > > +/* phy_c45_probe_present - checks to see if a MMD is present in the package > > > + * @bus: the target MII bus > > > + * @prtad: PHY package address on the MII bus > > > + * @devad: PHY device (MMD) address > > > + * > > > + * Read the MDIO_STAT2 register, and check whether a device is responding > > > + * at this address. > > > + * > > > + * Returns: negative error number on bus access error, zero if no device > > > + * is responding, or positive if a device is present. > > > + */ > > > +static int phy_c45_probe_present(struct mii_bus *bus, int prtad, int devad) > > > +{ > > > + int stat2; > > > + > > > + stat2 = mdiobus_c45_read(bus, prtad, devad, MDIO_STAT2); > > > + if (stat2 < 0) > > > + return stat2; > > > + > > > + return (stat2 & MDIO_STAT2_DEVPRST) == MDIO_STAT2_DEVPRST_VAL; > > > +} > > > + > > > /* get_phy_c45_devs_in_pkg - reads a MMD's devices in package registers. > > > * @bus: the target MII bus > > > * @addr: PHY address on the MII bus > > > @@ -709,12 +731,25 @@ static int get_phy_c45_ids(struct mii_bus *bus, int addr, u32 *phy_id, > > > { > > > const int num_ids = ARRAY_SIZE(c45_ids->device_ids); > > > u32 *devs = &c45_ids->devices_in_package; > > > - int i, phy_reg; > > > + int i, ret, phy_reg; > > > /* Find first non-zero Devices In package. Device zero is reserved > > > * for 802.3 c45 complied PHYs, so don't probe it at first. > > > */ > > > - for (i = 1; i < num_ids && *devs == 0; i++) { > > > + for (i = 1; i < MDIO_MMD_NUM && *devs == 0; i++) { > > > + if (i >= 8) { > > > + /* Only probe for the devices-in-package if there > > > + * is a PHY reporting as present here; this avoids > > > + * picking up on PHYs that implement non-IEEE802.3 > > > + * compliant register spaces. > > > + */ > > > + ret = phy_c45_probe_present(bus, addr, i); > > > + if (ret < 0) > > > + return -EIO; > > > + > > > + if (!ret) > > > + continue; > > > + } > > > > A second look at 802.3, this can't be done for all MMDs (which becomes > > visible when I look at the results from the 88x3310.) Only MMDs 1, 2, > > 3, 4, 5, 30 and 31 are defined to have this register with the "Device > > Present" bit pair. > > > > I'm not sure it helps, but my thought process following some of the > discussion last night was: > > something to the effect: > > for (i = 1; i < MDIO_MMD_NUM && *devs == 0; i++) { > + if (i & RESERVED_MMDS) > + continue; > > where RESERVED_MMDS was a hardcoded bitfield matching the IEEE reserved > MMDs. or maybe a "IGNORE_MMDS" which also includes BIT0 and other MMDs the > code doesn't understand. That seems to be walking into a mine field - which MMDs are reserved depends on which revision of the IEEE 802.3 specification you look at: Spec version Reserved MMDs 2012, 2015 0, 12-28 2018 0, 14-28 and as technology progresses, it's likely more MMDs will no longer be reserved. There is another problem: 802.3 explicitly defines the devices in package registers for MMD 1, 2, 3, 4, 5, 6, 7, and 29, but then goes on to say: "Each MMD contains registers 5 and 6, as defined in Table 45-2." which seems rather contradictory. There is also the problem that some PHYs have different values in their devices-in-package register for each MMD: MMD devices-in-package 1,3,7 c000009a 4 4000001a 30 00000000 (device present = not present) 31 fffe0000 (device present = not present) What fun. Thankfully, MMD1 will be read first, so it doesn't cause us a problem. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTC for 0.8m (est. 1762m) line in suburbia: sync at 13.1Mbps down 424kbps up
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