Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932273Ab3GVOoo (ORCPT ); Mon, 22 Jul 2013 10:44:44 -0400 Received: from iolanthe.rowland.org ([192.131.102.54]:36683 "HELO iolanthe.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S932101Ab3GVOok (ORCPT ); Mon, 22 Jul 2013 10:44:40 -0400 Date: Mon, 22 Jul 2013 10:44:39 -0400 (EDT) From: Alan Stern X-X-Sender: stern@iolanthe.rowland.org To: Kishon Vijay Abraham I cc: Sylwester Nawrocki , Greg KH , Sascha Hauer , , , , , , , , , , , , , , , , , , , , , , Subject: Re: [PATCH 01/15] drivers: phy: add generic PHY framework In-Reply-To: <51ECDE5E.3050104@ti.com> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4365 Lines: 105 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? > > 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? > > 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. > > Probably some of the details above are wrong; please indicate where I > > have gone astray. Also, I'm not clear about the role played by various > > APIs. For example, where does phy_create() fit into this picture? > > phy_create is the API by which the PHY's driver (the supplier) hook into the > PHY framework. It's like the controller driver will always interact with the > PHY driver through the PHY framework. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/