Re: [RFC PATCH v2 01/16] ACPI: Add support for device specific properties

Mika Westerberg
2014-10-06T14:32:48Z

On Mon, Oct 06, 2014 at 02:50:21PM +0100, Grant Likely wrote:
> On Tue, 16 Sep 2014 14:52:32 +0300
> , Mika Westerberg <mika.westerberg-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>
> wrote:
> > Device Tree is used in many embedded systems to describe the system
> > configuration to the OS. It supports attaching properties or name-value
> > pairs to the devices it describe. With these properties one can pass
> > additional information to the drivers that would not be available
> > otherwise.
> >
> > ACPI is another configuration mechanism (among other things) typically
> > seen, but not limited to, x86 machines. ACPI allows passing arbitrary
> > data from methods but there has not been mechanism equivalent to Device
> > Tree until the introduction of _DSD in the recent publication of the
> > ACPI 5.1 specification.
> >
> > In order to facilitate ACPI usage in systems where Device Tree is
> > typically used, it would be beneficial to standardize a way to retrieve
> > Device Tree style properties from ACPI devices, which is what we do in
> > this patch.
> >
> > If a given device described in ACPI namespace wants to export properties it
> > must implement _DSD method (Device Specific Data, introduced with ACPI 5.1)
> > that returns the properties in a package of packages. For example:
> >
> > Name (_DSD, Package () {
> > ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
> > Package () {
> > Package () {"name1", <VALUE1>},
> > Package () {"name2", <VALUE2>},
> > ...
> > }
> > })
> >
> > The UUID reserved for properties is daffd814-6eba-4d8c-8a91-bc9bbf4aa301
> > and is documented in the ACPI 5.1 companion document called "_DSD
> > Implementation Guide" [1], [2].
> >
> > We add several helper functions that can be used to extract these
> > properties and convert them to different Linux data types.
> >
> > The ultimate goal is that we only have one device property API that
> > retrieves the requested properties from Device Tree or from ACPI
> > transparent to the caller.
> >
> > [1] http://www.uefi.org/sites/default/files/resources/_DSD-implementation-guide-toplevel.htm
> > [2] http://www.uefi.org/sites/default/files/resources/_DSD-device-properties-UUID.pdf
> >
> > Reviewed-by: Hanjun Guo <hanjun.guo-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
> > Reviewed-by: Josh Triplett <josh-iaAMLnmF4UmaiuxdJuQwMA@public.gmane.org>
> > Signed-off-by: Darren Hart <dvhart-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>
> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
> > Signed-off-by: Mika Westerberg <mika.westerberg-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>
> > ---
> > drivers/acpi/Makefile | 1 +
> > drivers/acpi/internal.h | 6 +
> > drivers/acpi/property.c | 364 ++++++++++++++++++++++++++++++++++++++++++++++++
> > drivers/acpi/scan.c | 2 +
> > include/acpi/acpi_bus.h | 7 +
> > include/linux/acpi.h | 40 ++++++
> > 6 files changed, 420 insertions(+)
> > create mode 100644 drivers/acpi/property.c
> >
> > diff --git a/drivers/acpi/Makefile b/drivers/acpi/Makefile
> > index 505d4d79fe3e..ba2cafe18fe4 100644
> > --- a/drivers/acpi/Makefile
> > +++ b/drivers/acpi/Makefile
> > @@ -46,6 +46,7 @@ acpi-y += acpi_pnp.o
> > acpi-y += power.o
> > acpi-y += event.o
> > acpi-y += sysfs.o
> > +acpi-y += property.o
> > acpi-$(CONFIG_X86) += acpi_cmos_rtc.o
> > acpi-$(CONFIG_DEBUG_FS) += debugfs.o
> > acpi-$(CONFIG_ACPI_NUMA) += numa.o
> > diff --git a/drivers/acpi/internal.h b/drivers/acpi/internal.h
> > index 4c5cf77e7576..e34290c7af9f 100644
> > --- a/drivers/acpi/internal.h
> > +++ b/drivers/acpi/internal.h
> > @@ -181,4 +181,10 @@ struct platform_device *acpi_create_platform_device(struct acpi_device *adev);
> > bool acpi_osi_is_win8(void);
> > #endif
> >
> > +/*--------------------------------------------------------------------------
> > + Device properties
> > + -------------------------------------------------------------------------- */
> > +void acpi_init_properties(struct acpi_device *adev);
> > +void acpi_free_properties(struct acpi_device *adev);
> > +
> > #endif /* _ACPI_INTERNAL_H_ */
> > diff --git a/drivers/acpi/property.c b/drivers/acpi/property.c
> > new file mode 100644
> > index 000000000000..c4a3e800e82c
> > --- /dev/null
> > +++ b/drivers/acpi/property.c
> > @@ -0,0 +1,364 @@
> > +/*
> > + * ACPI device specific properties support.
> > + *
> > + * Copyright (C) 2014, Intel Corporation
> > + * All rights reserved.
> > + *
> > + * Authors: Mika Westerberg <mika.westerberg-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>
> > + * Darren Hart <dvhart-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>
> > + * Rafael J. Wysocki <rafael.j.wysocki-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
> > + *
> > + * This program is free software; you can redistribute it and/or modify
> > + * it under the terms of the GNU General Public License version 2 as
> > + * published by the Free Software Foundation.
> > + */
> > +
> > +#include <linux/acpi.h>
> > +#include <linux/device.h>
> > +#include <linux/export.h>
> > +
> > +#include "internal.h"
> > +
> > +/* ACPI _DSD device properties UUID: daffd814-6eba-4d8c-8a91-bc9bbf4aa301 */
> > +static const u8 prp_uuid[16] = {
> > + 0x14, 0xd8, 0xff, 0xda, 0xba, 0x6e, 0x8c, 0x4d,
> > + 0x8a, 0x91, 0xbc, 0x9b, 0xbf, 0x4a, 0xa3, 0x01
> > +};
>
> ?
>
> What is the encoding used here? I see the first 4 bytes for "daffd814"
> encoded in little endian (0x14 first), and then the remaining values
> encoded in big-endian for each number. Is this typical for UUID values?

The buffer format is explained in ACPI 5.1 spec, page 823.

I generated the above so that I compiled a _DSD with correct UUID using
iASL and then disassambled it with the same tool.
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