[alsa-devel] [PATCH] ACPI / device_sysfs: change _ADR representation to 64 bits

[Rafael J. Wysocki]

On Tue, Apr 16, 2019 at 5:29 AM Vinod Koul <vkoul at kernel.org> wrote:
>
> On 15-04-19, 10:18, Pierre-Louis Bossart wrote:
> > Standards such as the MIPI DisCo for SoundWire 1.0 specification
> > assume the _ADR field is 64 bits.
> >
> > _ADR is defined as an "Integer" represented as 64 bits since ACPI 2.0
> > released in 2002. The low levels already use _ADR as 64 bits, e.g. in
> > struct acpi_device_info.
> >
> > This patch bumps the representation used for sysfs to 64 bits.
> >
> > Example with a SoundWire device, the results show the complete
> > vendorID and linkID which were omitted before:
> >
> > Before:
> > $ more /sys/bus/acpi/devices/device\:38/adr
> > 0x5d070000
> > After:
> > $ more /sys/bus/acpi/devices/device\:38/adr
> > 0x000010025d070000
>
> This looks fine but the sysfs file is an ABI. Not sure if we can modify
> the value returned this way.. Though it should not cause userspace
> reading 32bits to break...

Well, IIRC using "08" instead of "016" in the format field would
preserve the existing behavior for 32-bit values, wouldn't it?