On 8/28/19 8:41 AM, Ong, Boon Leong wrote: >> 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 & Florian, thanks for your review on this patch and insights on it. > We will look into the implementation as suggested as follow. > > - for each bit clear in mii_bus::phy_mask, scan it as C22 > - for each bit clear in mii_bus::phy_c45_mask, scan it as C45 > > We will work on this and resubmit soonest.
Sounds good. If you do not need to scan the MDIO bus, another approach is to call get_phy_device() by passing the is_c45 boolean to true in order to connect directly to a C45 device for which you already know the address. Assuming this is done for the stmmac PCI changes that you have submitted, and that those cards have a fixed set of addresses for their PHYs, maybe scanning the bus is overkill? -- Florian