Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752845Ab2KFUgT (ORCPT ); Tue, 6 Nov 2012 15:36:19 -0500 Received: from mail-wi0-f172.google.com ([209.85.212.172]:48736 "EHLO mail-wi0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752510Ab2KFUgS (ORCPT ); Tue, 6 Nov 2012 15:36:18 -0500 MIME-Version: 1.0 In-Reply-To: <1815967.2MF0PyW36l@vostro.rjw.lan> References: <1351928793-14375-1-git-send-email-mika.westerberg@linux.intel.com> <4052192.ry8JrGTr6H@vostro.rjw.lan> <1815967.2MF0PyW36l@vostro.rjw.lan> From: Bjorn Helgaas Date: Tue, 6 Nov 2012 13:35:56 -0700 Message-ID: Subject: Re: [PATCH 2/3] spi / ACPI: add ACPI enumeration support To: "Rafael J. Wysocki" Cc: Mika Westerberg , linux-kernel@vger.kernel.org, lenb@kernel.org, rafael.j.wysocki@intel.com, broonie@opensource.wolfsonmicro.com, grant.likely@secretlab.ca, linus.walleij@linaro.org, khali@linux-fr.org, ben-linux@fluff.org, w.sang@pengutronix.de, mathias.nyman@linux.intel.com, linux-acpi@vger.kernel.org Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4956 Lines: 95 On Tue, Nov 6, 2012 at 6:43 AM, Rafael J. Wysocki wrote: > On Monday, November 05, 2012 09:54:42 AM Bjorn Helgaas wrote: >> On Mon, Nov 5, 2012 at 3:31 AM, Rafael J. Wysocki wrote: >> > On Saturday, November 03, 2012 09:59:28 PM Rafael J. Wysocki wrote: >> >> On Saturday, November 03, 2012 10:13:10 PM Mika Westerberg wrote: >> >> > On Sat, Nov 03, 2012 at 01:42:02PM -0600, Bjorn Helgaas wrote: >> >> > > On Sat, Nov 3, 2012 at 1:46 AM, Mika Westerberg >> >> > > wrote: >> >> > > > ACPI 5 introduced SPISerialBus resource that allows us to enumerate and >> >> > > > configure the SPI slave devices behind the SPI controller. This patch adds >> >> > > > support for this to the SPI core. >> > [...] >> >> > And if the ACPI core parses the _CRS, how does it pass all the resources to >> >> > the drivers? >> >> >> >> Pretty much the same way the $subject patch does. >> >> >> >> Instead of parsing the entire subtree below an SPI controller and trying >> >> acpi_spi_add_device() for each device node in there, it could call >> >> acpi_spi_add_device() whenever it finds a device of type >> >> ACPI_RESOURCE_TYPE_SERIAL_BUS/ACPI_RESOURCE_SERIAL_TYPE_SPI. >> >> The only problem is how to pass "master" to it. >> >> >> >> So Bjorn, do you have any idea how we could pass the "master" pointer from the >> >> ACPI core to acpi_spi_add_device() in a sensible way? >> >> >> >> An alternative might be to store the information obtained from _CRS in >> >> struct acpi_device objects created by the ACPI core while parsing the >> >> namespace. We do that already for things like _PRW, so we might as well do it >> >> for _CRS. Then, the SPI core could just walk the subtree of the device hierarchy >> >> below the SPI controller's acpi_device to extract that information. >> >> Maybe that's the way to go? >> > >> > The general idea is to move the _CRS parsing routine from acpi_platform.c >> > to scan.c and make it attach resource objects to struct acpi_device. >> > >> > I'm thinking about adding a list head to struct acpi_device pointing to a >> > list of entries like: >> > >> > struct resource_list_entry { >> > struct list_head node; >> > struct resource *resources; >> > unsigned int count; >> > }; >> > >> > where "resources" is an array of resources (e.g. interrupts) in the given >> > entry and count is the size of that array. >> > >> > That list would contain common resources like ACPI_RESOURCE_TYPE_FIXED_MEMORY32, >> > ACPI_RESOURCE_TYPE_IRQ, ACPI_RESOURCE_TYPE_ADDRESS32, ACPI_RESOURCE_TYPE_EXTENDED_IRQ. >> >> This is exactly what PNPACPI already does. For every Device node in >> the namespace, pnpacpi/rsparser.c parses _CRS and builds a list of >> struct resources that correspond to it. If you put this functionality >> in acpi/scan.c, should we get rid of PNPACPI? > > Quite likely. At least this part of it, if you want the core to parse > resources. > > That said, I actually tried to abstract out resource parsing in a more generic > fashion on the basis of our new platform device support code, but quite frankly > I wasn't able to. > > The problem is that struct resource is too simple to be useful for representing > all of the information that can be encoded in ACPI resources. As a result, some > information have to be stored directly in things like struct pnp_dev, struct > platform_device etc. and if we want to represent it generically, the only way > to do that seems to be using the ACPICA resource types as defined in acrestyp.h. Really? I didn't have that impression. It might be that the new GPIO and SERIAL_BUS stuff makes it too complicated for a struct resource, but prior to that, I don't think it was. It's true that there are many different formats (IO, FIXED_IO, MEMORY24, MEMORY32, etc.), but only the core needs to be aware of the encoding of all those formats. As far as a *driver* is concerned, there are only IRQ, DMA, IO, and MEM resources, and those fit easily in a struct resource. I want to expand on what I said before about _CRS being the domain of the core, not drivers. The core must evaluate _CRS to know where devices are and avoid conflicts when assigning resources. The core must evaluate _PRS and _SRS when making resource assignments. It doesn't make sense for drivers to be using _PRS and _SRS; they don't have a global view of resources, and any assignment they make would likely cause conflicts with other devices. I think it makes sense to consolidate all _CRS, _PRS, and _SRS management in the core rather than splitting it up. This is exactly analogous to PCI BAR management, and we don't intend drivers to read and write BARs directly. Bjorn -- 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/