linux-kernel - Re: [PATCH] ACPI / device_sysfs: change

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Message-ID: <CAJZ5v0jOkQ7aWn6B_yVTYd7y+78mpGSzBoGuWe3uCdzDRNE94Q@mail.gmail.com>
Date:   Tue, 16 Apr 2019 10:09:57 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Vinod Koul <vkoul@...nel.org>
Cc:     Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>,
        "moderated list:SOUND - SOC LAYER / DYNAMIC AUDIO POWER MANAGEM..." 
        <alsa-devel@...a-project.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Takashi Iwai <tiwai@...e.de>, Mark Brown <broonie@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Liam Girdwood <liam.r.girdwood@...ux.intel.com>,
        jank@...ence.com, Joe Perches <joe@...ches.com>,
        Srini Kandagatla <srinivas.kandagatla@...aro.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>,
        Robert Moore <robert.moore@...el.com>,
        Erik Schmauss <erik.schmauss@...el.com>,
        "open list:ACPI" <linux-acpi@...r.kernel.org>,
        "open list:ACPI COMPONENT ARCHITECTURE (ACPICA)" <devel@...ica.org>
Subject: Re: [PATCH] ACPI / device_sysfs: change _ADR representation to 64 bits

On Tue, Apr 16, 2019 at 5:29 AM Vinod Koul <vkoul@...nel.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?