Thanks Andrew and Jeremy for the detailed discussion! On Fri, May 08, 2020 at 08:13:01PM +0200, Andrew Lunn wrote: > > > It does have a numeric version defined for EISA types. OTOH I suspect that > > > your right. If there were a "PHY\VEN_IDvvvv&ID_DDDD" definition, it may not > > > be ideal to parse it. Instead the normal ACPI model of exactly matching the > > > complete string in the phy driver might be more appropriate. > > > > IMO, it should be fine to parse the string to extract the phy_id. Is there any > > reason why we cannot do this? > > Some background here, about what the PHY core does. > > PHYs have two ID registers. This contains vendor, device, and often > revision of the PHY. Only the vendor part is standardised, vendors can > decide how to use the device part, but it is common for the lowest > nibble to be revision. The core will read these ID registers, and then > go through all the PHY drivers registered and ask them if they support > this ID. The drivers provide a table of IDs and masks. The mask is > applied, and then if the ID matches, the driver is used. The mask > allows the revision to be ignored, etc. > > There is a very small number of devices where the vendor messed up, > and did not put valid contents in the ID registers. In such cases, we > can read the IDs from device tree. These are then used in exactly the > same way as if they were read from the device. > > If you want the ACPI model to be used, an exact match on the string, > you are going to have to modify the core and the drivers. They > currently don't have any string, and have no idea about different > revisions which are out in the wild. I don't think ACPI mandates that OS driver use exact string match and not parse the string. First of all, I would suggest that we use "compatible" property instead of _CID. Not sure of a reason why we cannot. This will simplify implementation of fwnode APIs. Already I've pointed out couple of ASL files in tianocore where they are already used. one eg:https://github.com/tianocore/edk2-platforms/blob/master/Silicon/Marvell/Armada7k8k/AcpiTables/Armada80x0McBin/Dsdt.asl#L280 Even if we use _CID, I'm not sure we are prohibited from extracting characters (phy_id) from it. If we decide to use _CID, then we need to define somewhere and standardize exactly how we are going to use it. I'm not sure where we can do this. > > > > Similarly to how I suspect the next patch's use of "compatible" isn't ideal > > > either, because whether a device is c45 or not, should tend to be fixed to a > > > particular vendor/device implementation and not a firmware provided > > > property. > > Not exactly true. It is the combination of can the bus master do C45 > and can the device do C45. Unfortunately, we have no knowledge of the > bus masters capabilities, if it can do C45. And many MDIO drivers will > do a C22 transaction when asked to perform a C45 transaction. All new > submissions for MDIO drivers i ask for EOPNOTSUPP to be returned if > C45 is not supported. But we cannot rely on that. Too much history. Makes sense to me. > > > > I tend to agree with you on this. Even for DT, ideal case, IMO should be: > > > > 1) mdiobus_scan scans the mdiobus for c22 devices by reading phy id from > > registers 2 and 3 > > 2) if not found scan for c45 devices <= looks like this is missing in Linux > > 3) look for phy_id from compatible string. > > It is somewhat more complex, in that there are a small number of > devices which will respond to both C22 and C45. Generally, you want to > use C45 if supported. So you would want to do the C45 scan first. But > then the earlier problem comes to play, you have no idea if the bus > master actually correctly supports C45. > > Given the issues, we assume all bus masters and PHY devices are C22 > unless DT says the bus master and PHY combination is compatible with > C45. Makes sense to me.
