Re: [PATCH v3 2/3] acpi: dptf_power: Add DPTF power participant

["Rafael J. Wysocki" <rafael@kernel.org>]

On Mon, Jun 27, 2016 at 3:31 AM, Srinivas Pandruvada
<srinivas.pandruvada@linux.intel.com> wrote:
> On Fri, 2016-06-24 at 02:26 +0200, Rafael J. Wysocki wrote:
>> > > >
>> On Fri, Jun 24, 2016 at 1:19 AM, Srinivas Pandruvada
>> <srinivas.pandruvada@linux.intel.com> wrote:
>> > On Fri, 2016-06-24 at 00:31 +0200, Rafael J. Wysocki wrote:
>> > > On Thu, Jun 23, 2016 at 11:42 PM, Srinivas Pandruvada
>> > > <srinivas.pandruvada@linux.intel.com> wrote:
> [...]
>
>> I think what you need is that if acpi_battery is bound to at least
>> one
>> device, you don't want to bind dptf_power to anything.  Conversely,
>> if
>> dptf_power has been bound to at least one device, you don't want to
>> bind acpi_battery to anything.
>>
>> That may be achieved with a lock and two counters, one (A)
>> incremented
>> only by acpi_battery and the other (B) incremented only by dptf_power
>> and such that you can't increment A if B is different from 0 and you
>> can't increment B if A is different from 0.  Of course, each driver
>> would need to specify which counter it wants to use (A or B), so that
>> would take an additional argument to acpi_battery_common_add() and an
>> additional field in struct acpi_battery (for the remove operation).
>>
>> With that, I think it should only be possible to build both
>> acpi_battery and dptf_power if they are both modules.  IOW,
>> DPTF_POWER
>> should depend on (!ACPI_BATTERY || ACPI_BATTERY=m) or similar.  And
>> if
>> they are both modules, let user space manage that.
>>
>> And the waiting itself doesn't add any value then IMO.
> Yes. I think the best solution is not to let define DPTF_POWER when the
> ACPI_BATTERY is defined same as my first version of the patch or let
> both add as there is no harm as they will show same levels. The reason
> is:
> We have some devices with two ACPI_BATTERIES (primary and
> secondary/backup) and they must be presented as two power supply
> devices to user space. In those devices DPTF_POWER may be equivalent to
> only one of the ACPI_BATTERY (Will point to same battery for Battery
> levels). So we can't simply refuse to add ACPI_BATTERY device addition
> because DPTF_POWER device is registered before.

OK

Say dptf_power points to the same battery device as acpi_battery.  Is
there any way to tell when that happens?