Re: [PATCH 1/2] ACPI: utils: Add acpi_reduced_hardware() helper

[Hans de Goede <hdegoede@redhat.com>]

Hi,

On 4/7/21 7:50 PM, Rafael J. Wysocki wrote:
> On Wed, Apr 7, 2021 at 7:43 PM Hans de Goede <hdegoede@redhat.com> wrote:
>>
>> Hi,
>>
>> On 4/7/21 7:13 PM, Rafael J. Wysocki wrote:
>>> On Tue, Apr 6, 2021 at 11:17 PM Hans de Goede <hdegoede@redhat.com> wrote:
>>>>
>>>> Add a getter for the acpi_gbl_reduced_hardware variable so that modules
>>>> can check if they are running on an ACPI reduced-hw platform or not.
>>>>
>>>> Signed-off-by: Hans de Goede <hdegoede@redhat.com>
>>>> ---
>>>>  drivers/acpi/utils.c    | 11 +++++++++++
>>>>  include/acpi/acpi_bus.h |  1 +
>>>>  include/linux/acpi.h    |  5 +++++
>>>>  3 files changed, 17 insertions(+)
>>>>
>>>> diff --git a/drivers/acpi/utils.c b/drivers/acpi/utils.c
>>>> index 682edd913b3b..4cb061d3169a 100644
>>>> --- a/drivers/acpi/utils.c
>>>> +++ b/drivers/acpi/utils.c
>>>> @@ -872,6 +872,17 @@ acpi_dev_get_first_match_dev(const char *hid, const char *uid, s64 hrv)
>>>>  }
>>>>  EXPORT_SYMBOL(acpi_dev_get_first_match_dev);
>>>>
>>>> +/**
>>>> + * acpi_reduced_hardware - Return if this is an ACPI-reduced-hw machine
>>>> + *
>>>> + * Return true when running on an ACPI-reduced-hw machine, false otherwise.
>>>> + */
>>>> +bool acpi_reduced_hardware(void)
>>>> +{
>>>> +       return acpi_gbl_reduced_hardware;
>>>> +}
>>>> +EXPORT_SYMBOL(acpi_reduced_hardware);
>>>
>>> EXPORT_SYMBOL_GPL()?
>>
>> Yes, that was my intention, no idea what happened here.

I just prepped and send out v2 and I think I know what happened, all
the other functions in drivers/acpi/utils.c are EXPORT_SYMBOL, so I probably
just copy-and-pasted this without too much thinking.

It might be worthwhile to see if we should also mark some other functions
as EXPORT_SYMBOL_GPL() here.

>> Before I send a v2, do you have any remarks on patch 2/2 (which is actually
>> the more interesting patch) ?
> 
> I thought that basing that check on the ACPICA's global variable may
> be too coarse grained for some cases, but then I've decided to do it
> as is now and we'll see.

Yes, the whole code for selecting which backlight driver to use is mostly
heuristics, so "we'll see" indeed . With that said I'm pretty confident
that this change should not cause problems. Platforms which actually
set acpi_gbl_reduced_hardware=true seem to be quite rare. I'm actually
only aware of Bay Trail-T based devices doing this.

Regards,

Hans