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

[Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>]

On 4/16/19 3:09 AM, Rafael J. Wysocki wrote:
> On Tue, Apr 16, 2019 at 5:29 AM Vinod Koul <vkoul@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?

yes, but it makes the 64-bit address not aligned depending on the number 
of leading zeroes, see below. I get a migraine just looking at the results.

Maybe add a test to use 08 for values that are below 0xFFFFFFFF and 16 
for addresses who really need the full range, typically because of an 
encoding?

w/ value-dependent format:
/sys/bus/acpi/devices# cat */*/adr

0x00160000
0x00140003
0x000d0000
0x000d0002
0x000d0003
0x00070000
0x00070001
0x00070002
0x00070003
0x000010025d070100
0x000110025d070100
0x000210025d070100
0x000310025d070100
0x000010025d070000
0x000110025d070000
0x000210025d070000
0x000310025d070000
0x00000000

w/ 0x08 only:

0x00160000
0x00140003
0x000d0000
0x000d0002
0x000d0003
0x00070000
0x00070001
0x00070002
0x00070003
0x10025d070100
0x110025d070100
0x210025d070100
0x310025d070100
0x10025d070000
0x110025d070000
0x210025d070000
0x310025d070000
0x00000000
0x00000000