[Fixed address of devicetree mailing list and added more people on CC.] For reference, full thread can be found under following link: http://thread.gmane.org/gmane.linux.ports.arm.kernel/252813 Best regards, Tomasz On Tuesday 23 of July 2013 09:29:32 Tomasz Figa wrote: > Hi Alan, > > On Monday 22 of July 2013 10:44:39 Alan Stern wrote: > > On Mon, 22 Jul 2013, Kishon Vijay Abraham I wrote: > > > > The PHY and the controller it is attached to are both physical > > > > devices. > > > > > > > > The connection between them is hardwired by the system > > > > manufacturer and cannot be changed by software. > > > > > > > > PHYs are generally described by fixed system-specific board > > > > files or by Device Tree information. Are they ever discovered > > > > dynamically? > > > > > > No. They are created just like any other platform devices are > > > created. > > > > Okay. Are PHYs _always_ platform devices? > > They can be i2c, spi or any other device types as well. > > > > > Is the same true for the controllers attached to the PHYs? > > > > If not -- if both a PHY and a controller are discovered > > > > dynamically -- how does the kernel know whether they are > > > > connected to each other? > > > > > > No differences here. Both PHY and controller will have dt > > > information > > > or hwmod data using which platform devices will be created. > > > > > > > The kernel needs to know which controller is attached to which > > > > PHY. Currently this information is represented by name or ID > > > > strings embedded in platform data. > > > > > > right. It's embedded in the platform data of the controller. > > > > It must also be embedded in the PHY's platform data somehow. > > Otherwise, how would the kernel know which PHY to use? > > By using a PHY lookup as Stephen and I suggested in our previous > replies. Without any extra data in platform data. (I have even posted a > code example.) > > > > > The PHY's driver (the supplier) uses the platform data to > > > > construct a platform_device structure that represents the PHY. > > > > > > Currently the driver assigns static labels (corresponding to the > > > label > > > used in the platform data of the controller). > > > > > > > Until this is done, the controller's driver (the client) cannot > > > > use the PHY. > > > > > > right. > > > > > > > Since there is no parent-child relation between the PHY and the > > > > controller, there is no guarantee that the PHY's driver will be > > > > ready when the controller's driver wants to use it. A deferred > > > > probe may be needed. > > > > > > right. > > > > > > > The issue (or one of the issues) in this discussion is that > > > > Greg does not like the idea of using names or IDs to associate > > > > PHYs with controllers, because they are too prone to > > > > duplications or other errors. Pointers are more reliable. > > > > > > > > But pointers to what? Since the only data known to be > > > > available to both the PHY driver and controller driver is the > > > > platform data, the obvious answer is a pointer to platform data > > > > (either for the PHY or for the controller, or maybe both). > > > > > > hmm.. it's not going to be simple though as the platform device for > > > the PHY and controller can be created in entirely different places. > > > e.g., in some cases the PHY device is a child of some mfd core > > > device > > > (the device will be created in drivers/mfd) and the controller > > > driver > > > (usually) is created in board file. I guess then we have to come up > > > with something to share a pointer in two different files. > > > > The ability for two different source files to share a pointer to a > > data > > item defined in a third source file has been around since long before > > the C language was invented. :-) > > > > In this case, it doesn't matter where the platform_device structures > > are created or where the driver source code is. Let's take a simple > > example. Suppose the system design includes a PHY named "foo". Then > > the board file could contain: > > > > struct phy_info { ... } phy_foo; > > EXPORT_SYMBOL_GPL(phy_foo); > > > > and a header file would contain: > > > > extern struct phy_info phy_foo; > > > > The PHY supplier could then call phy_create(&phy_foo), and the PHY > > client could call phy_find(&phy_foo). Or something like that; make up > > your own structure tags and function names. > > > > It's still possible to have conflicts, but now two PHYs with the same > > name (or a misspelled name somewhere) will cause an error at link > > time. > > This is incorrect, sorry. First of all it's a layering violation - you > export random driver-specific symbols from one driver to another. Then > imagine 4 SoCs - A, B, C, D. There are two PHY types PHY1 and PHY2 and > there are two types of consumer drivers (e.g. USB host controllers). Now > consider following mapping: > > SoC PHY consumer > A PHY1 HOST1 > B PHY1 HOST2 > C PHY2 HOST1 > D PHY2 HOST2 > > So we have to be able to use any of the PHYs with any of the host > drivers. This means you would have to export symbol with the same name > from both PHY drivers, which obviously would not work in this case, > because having both drivers enabled (in a multiplatform aware > configuration) would lead to linking conflict. > > Best regards, > Tomasz -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
