linux-kernel - Re: [V3 PATCH 1/2] ACPI / scan: Add support for ACPI

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Date:	Tue, 10 Feb 2015 11:59:32 +0200
From:	Mika Westerberg <mika.westerberg@...ux.intel.com>
To:	"Suthikulpanit, Suravee" <Suravee.Suthikulpanit@....com>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"lenb@...nel.org" <lenb@...nel.org>,
	"hdegoede@...hat.com" <hdegoede@...hat.com>,
	"tj@...nel.org" <tj@...nel.org>, "arnd@...db.de" <arnd@...db.de>,
	"mjg59@...f.ucam.org" <mjg59@...f.ucam.org>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	"hanjun.guo@...aro.org" <hanjun.guo@...aro.org>,
	"al.stone@...aro.org" <al.stone@...aro.org>,
	"graeme.gregory@...aro.org" <graeme.gregory@...aro.org>,
	"Duran, Leo" <leo.duran@....com>,
	"linux-ide@...r.kernel.org" <linux-ide@...r.kernel.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linaro-acpi@...ts.linaro.org" <linaro-acpi@...ts.linaro.org>,
	Lv Zheng <lv.zheng@...el.com>
Subject: Re: [V3 PATCH 1/2] ACPI / scan: Add support for ACPI _CLS device
 matching

On Mon, Feb 09, 2015 at 09:02:11PM +0000, Suthikulpanit, Suravee wrote:
> On 2/9/15, 19:15, "Mika Westerberg" <mika.westerberg@...ux.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@....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. Besides, how do you
support modules with this? Or did I miss something?
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