Re: [V3 PATCH 1/2] ACPI / scan: Add support for ACPI _CLS device matching

["Rafael J. Wysocki" <rjw@rjwysocki.net>]

On Tuesday, February 10, 2015 11:59:32 AM Mika Westerberg wrote:
> On Mon, Feb 09, 2015 at 09:02:11PM +0000, Suthikulpanit, Suravee wrote:
> > On 2/9/15, 19:15, "Mika Westerberg" <mika.westerberg@linux.intel.com>
> > wrote:
> > 
> > >On Mon, Feb 09, 2015 at 12:02:43AM +0100, Rafael J. Wysocki wrote:
> > >> On Monday, February 09, 2015 12:20:03 AM Suravee Suthikulpanit wrote:
> > >> > Device drivers typically use ACPI _HIDs/_CIDs listed in struct
> > >>device_driver
> > >> > acpi_match_table to match devices. However, for generic drivers, we do
> > >> > not want to list _HID for all supported devices, and some device
> > >>classes
> > >> > do not have _CID (e.g. SATA, USB). Instead, we can leverage ACPI _CLS,
> > >> > which specifies PCI-defined class code (i.e. base-class, subclass and
> > >> > programming interface).
> > >> > 
> > >> > This patch adds support for matching ACPI devices using the _CLS
> > >>method.
> > >> > 
> > >> > Signed-off-by: Suravee Suthikulpanit <Suravee.Suthikulpanit@amd.com>
> > >> 
> > >> Greg, Mika, any problems with this?
> > >
> > >Is there some specific reason why this cannot be done in similar way
> > >than PCI already does?
> > >
> > >In other words, stuff _CLS fields to struct acpi_device_id and make
> > >match functions match against those if they are != 0.
> > 
> > That was my original thought. Then I realized that the acpi_device_id is
> > used
> > to create the device matching table, in which could contain several
> > _HID/_CID.
> > However, most of the added _CLS field would likely ended up being unused
> > and
> > taking up space.
> 
> Well, PCI is doing that already :)
> 
> > In contrast to _HID/_CID, a driver is likely to match just a single _CLS.
> > So, I think it is cleaner to have just a dedicate struct acpi_device_cls,
> > and 
> > a matching function for it.
> 
> IMHO cleaner version is the one following PCI.

I agree.

> Besides, how do you support modules with this? Or did I miss something?

Good question.


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.