linux-kernel - Re: [V5 PATCH 1/2] ACPI / scan: Add support for ACPI

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Date:	Tue, 24 Mar 2015 16:43:46 +0200
From:	Mika Westerberg <mika.westerberg@...ux.intel.com>
To:	Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>
Cc:	rjw@...ysocki.net, lv.zheng@...el.com, hpa@...ux.intel.com,
	lenb@...nel.org, hdegoede@...hat.com, tj@...nel.org, arnd@...db.de,
	mjg59@...f.ucam.org, gregkh@...uxfoundation.org,
	hanjun.guo@...aro.org, al.stone@...aro.org,
	graeme.gregory@...aro.org, leo.duran@....com,
	linux-ide@...r.kernel.org, linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org, linaro-acpi@...ts.linaro.org
Subject: Re: [V5 PATCH 1/2] ACPI / scan: Add support for ACPI _CLS device
 matching

On Tue, Mar 24, 2015 at 09:23:47AM -0500, Suravee Suthikulpanit wrote:
> Not sure if this email went out originally. So, I am resending this.
> 
> On 3/9/15 10:20, Mika Westerberg wrote:
> >On Fri, Mar 06, 2015 at 12:11:41AM -0600, 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. Also, certain classes of devices
> >>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.
> >>
> >>To support loadable module, current design uses _HID or _CID to match device's
> >>modalias. With the new way of matching with _CLS this would requires modification
> >>to the current ACPI modalias key to include _CLS. This patch appends PCI-defined
> >>class-code to the existing ACPI modalias as following.
> >>
> >>     acpi:<HID>:<CID1>:<CID2>:..:<CIDn>:<bbsspp>:
> >>E.g:
> >>     # cat /sys/devices/platform/AMDI0600:00/modalias
> >>     acpi:AMDI0600:010601:
> >>
> >>where bb is th base-class code, ss is te sub-class code, and pp is the
> >>programming interface code
> >>
> >>Since there would not be _HID/_CID in the ACPI matching table of the driver,
> >>this patch adds a field to acpi_device_id to specify the matching _CLS.
> >>
> >>     static const struct acpi_device_id ahci_acpi_match[] = {
> >>         { "", 0, PCI_CLASS_STORAGE_SATA_AHCI },
> >
> >How about introducing macro like PCI already has and then do it like:
> >
> >	{ ACPI_DEVICE_CLASS(PCI_CLASS_STORAGE_SATA_AHCI) },
> 
> This is good.  I'll update this.
> >
> >Also should we allow mask here as well? This would allow partial match
> >if, for example we are only interested in class and subclass.
> 
> Hm, I'm not familiar with how other drivers might be benefit from this.
> Could you please give an example of a drivers that only deals with just the
> class and/or subclass of devices?

If you check for example drivers/ata/ata_generic.c it has this:

        { PCI_DEVICE_CLASS(PCI_CLASS_STORAGE_IDE << 8, 0xFFFFFF00UL),
	          .driver_data = ATA_GEN_CLASS_MATCH },

That seems to ignore programming interface.

> If so, could we use 0xFF to specify the don't care field?

In the above it seems that 0 is the don't care.

> >
> >>         {},
> >>     };
> >>
> >>In this case, the corresponded entry in modules.alias file would be:
> >>
> >>     alias acpi*:010601:* ahci_platform
> >>
> >>Signed-off-by: Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>
> >>---
> >>  drivers/acpi/acpica/acutils.h     |  3 ++
> >>  drivers/acpi/acpica/nsxfname.c    | 21 ++++++++++--
> >>  drivers/acpi/acpica/utids.c       | 71 +++++++++++++++++++++++++++++++++++++++
> >
> >I think you need to split the ACPICA part to be a separate patch. Those
> >are merged through ACPICA.
> 
> I will update this in the next patch set.
> 
> >>[....]
> >>diff --git a/include/linux/mod_devicetable.h b/include/linux/mod_devicetable.h
> >>index e530533..9a42522 100644
> >>--- a/include/linux/mod_devicetable.h
> >>+++ b/include/linux/mod_devicetable.h
> >>@@ -189,6 +189,7 @@ struct css_device_id {
> >>  struct acpi_device_id {
> >>  	__u8 id[ACPI_ID_LEN];
> >>  	kernel_ulong_t driver_data;
> >>+	__u32 cls;
> >
> >It would be nice if we could change ordering here but I understand that
> >it breaks quite many drivers. Perhaps we should consider creating
> >ACPI_DEVICE() macro and convert existing drivers to that at some point.
> 
> Yes, a roughly grep in the drivers directory showing about 112 files at the
> moment. If you think this is the right approach going forward, we can work
> on cleaning this up on a separate patch series. Please let me know what you
> think.

I think having ACPI_DEVICE() macro would be pretty useful and it avoids
things like this if we need to add new fields in the future. Rafael has
the last word, though :-)
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