On Tuesday 23 of July 2013 10:37:05 Alan Stern wrote: > On Tue, 23 Jul 2013, Tomasz Figa wrote: > > On Tuesday 23 of July 2013 09:29:32 Tomasz Figa wrote: > > > Hi Alan, > > Thanks for helping to clarify the issues here. > > > > > Okay. Are PHYs _always_ platform devices? > > > > > > They can be i2c, spi or any other device types as well. > > In those other cases, presumably there is no platform data associated > with the PHY since it isn't a platform device. Then how does the > kernel know which controller is attached to the PHY? Is this spelled > out in platform data associated with the PHY's i2c/spi/whatever parent? > > > > > > > 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.) > > I don't understand, because I don't know what "a PHY lookup" does.
I have provided a code example in [1]. Feel free to ask questions about those code snippets. [1] http://thread.gmane.org/gmane.linux.ports.arm.kernel/252813/focus=20889 > > > > 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 > > No, that's not what I said. Neither the PHY driver nor the controller > driver exports anything to the other. Instead, both drivers use data > exported by the board file. It's still a random, driver-specific global symbol exported from board file to drivers. > > > 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. > > You're right; the scheme was too simple. Instead, the board file must > export two types of data structures, one for PHYs and one for > controllers. Like this: > > struct phy_info { > /* Info for the controller attached to this PHY */ > struct controller_info *hinfo; > }; > > struct controller_info { > /* Info for the PHY which this controller is attached to */ > struct phy_info *pinfo; > }; > > The board file for SoC A would contain: > > struct phy_info phy1 = {&host1); > EXPORT_SYMBOL(phy1); > struct controller_info host1 = {&phy1}; > EXPORT_SYMBOL(host1); > > The board file for SoC B would contain: > > struct phy_info phy1 = {&host2); > EXPORT_SYMBOL(phy1); > struct controller_info host2 = {&phy1}; > EXPORT_SYMBOL(host2); > > And so on. This explicitly gives the connection between PHYs and > controllers. The PHY providers would use &phy1 or &phy2, and the PHY > consumers would use &host1 or &host2. This could work assuming that only one SoC and one board is supported in single kernel image. However it's not the case. We've used to support multiple boards since a long time already and now for selected platforms we even support multiplatform, i.e. multiple SoCs in single zImage. Such solution will not work. Best regards, Tomasz -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
