From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Rafael J. Wysocki" Subject: Re: [PATCH 2/3] spi / ACPI: add ACPI enumeration support Date: Tue, 06 Nov 2012 23:28:37 +0100 Message-ID: <1996776.cC14CHafyR@vostro.rjw.lan> References: <1351928793-14375-1-git-send-email-mika.westerberg@linux.intel.com> <1815967.2MF0PyW36l@vostro.rjw.lan> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7Bit Return-path: In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Bjorn Helgaas 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 List-Id: linux-acpi@vger.kernel.org On Tuesday, November 06, 2012 01:35:56 PM Bjorn Helgaas wrote: > 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. However, for example expanding ACPI_RESOURCE_TYPE_EXTENDED_IRQ into an array of struct resource objects before anyone actually needs it seems a bit wasteful to me. Let alone registering GSI for the interrupts while we're parsing those resources. > I want to expand on what I said before about _CRS being the domain of > the core, not drivers. Well, I see a difference between _evaluating_ _CRS and _parsing_ its output. In particular, I don't see a reason to do those two things in one operation. In fact, I see reasons to do otherwise. :-) > 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. OK, but then we need to pass the information obtained from _CRS (presumably after some adjustments through _SRS) to drivers, or rather to things like the SPI core, I2C core etc. so that they can create device objects for drivers to bind to and quite frankly I don't see why not to use ACPI resources for that. Thanks, Rafael -- I speak only for myself. Rafael J. Wysocki, Intel Open Source Technology Center.