On Tue, Aug 27, 2019 at 03:23:34PM +0000, Voon, Weifeng wrote: > > > > Make mdiobus_scan() to try harder to look for any PHY that only > > talks C45. > > > If you are not using Device Tree or ACPI, and you are letting the MDIO > > > bus be scanned, it sounds like there should be a way for you to > > > provide a hint as to which addresses should be scanned (that's > > > mii_bus::phy_mask) and possibly enhance that with a mask of possible > > > C45 devices? > > > > Yes, i don't like this unconditional c45 scanning. A lot of MDIO bus > > drivers don't look for the MII_ADDR_C45. They are going to do a C22 > > transfer, and maybe not mask out the MII_ADDR_C45 from reg, causing an > > invalid register write. Bad things can then happen. > > > > With DT and ACPI, we have an explicit indication that C45 should be used, > > so we know on this platform C45 is safe to use. We need something > > similar when not using DT or ACPI. > > > > Andrew > > Florian and Andrew, > The mdio c22 is using the start-of-frame ST=01 while mdio c45 is using ST=00 > as identifier. So mdio c22 device will not response to mdio c45 protocol. > As in IEEE 802.1ae-2002 Annex 45A.3 mention that: > " Even though the Clause 45 MDIO frames using the ST=00 frame code > will also be driven on to the Clause 22 MII Management interface, > the Clause 22 PHYs will ignore the frames. " > > Hence, I am not seeing any concern that the c45 scanning will mess up with > c22 devices.
Hi Voon Take for example mdio-hisi-femac.c static int hisi_femac_mdio_read(struct mii_bus *bus, int mii_id, int regnum) { struct hisi_femac_mdio_data *data = bus->priv; int ret; ret = hisi_femac_mdio_wait_ready(data); if (ret) return ret; writel((mii_id << BIT_PHY_ADDR_OFFSET) | regnum, data->membase + MDIO_RWCTRL); There is no check here for MII_ADDR_C45. So it will perform a C22 transfer. And regnum will still have MII_ADDR_C45 in it, so the writel() is going to set bit 30, since #define MII_ADDR_C45 (1<<30). What happens on this hardware under these conditions? You cannot unconditionally ask an MDIO driver to do a C45 transfer. Some drivers are going to do bad things. Andrew