[Intel-gfx] [PATCH] ACPI / bus: Introduce a list of ids for "always present" devices

[Takashi Iwai]

On Mon, 27 Feb 2017 15:25:32 +0100,
Hans de Goede wrote:
> 
> Hi,
> 
> On 27-02-17 14:30, Rafael J. Wysocki wrote:
> > +Mika & Andy
> >
> > On Saturday, February 25, 2017 07:23:28 PM Hans de Goede wrote:
> >> Several cherrytrail devices (all of which ship with windows 10) hide the
> >> lpss pwm controller in ACPI, typically the _STA method looks like this:
> >>
> >>     Method (_STA, 0, NotSerialized)  // _STA: Status
> >>     {
> >>         If (OSID == One)
> >>         {
> >>             Return (Zero)
> >>         }
> >>
> >>         Return (0x0F)
> >>     }
> >>
> >> Where OSID is some dark magic seen in all cherrytrail ACPI tables making
> >> the machine behave differently depending on which OS it *thinks* it is
> >> booting, this gets set in a number of ways which we cannot control, on
> >> some newer machines it simple hardcoded to "One" aka win10.
> >>
> >> This causes the PWM controller to get hidden, which means Linux cannot
> >> control the backlight level on cht based tablets / laptops.
> >>
> >> Since loading the driver for this does no harm (the only in kernel user
> >> of it is the i915 driver, which will only use it when it needs it), this
> >> commit makes acpi_bus_get_status() always set status to ACPI_STA_DEFAULT
> >> for the 80862288 device, fixing the lack of backlight control.
> >>
> >> Signed-off-by: Hans de Goede <hdegoede at redhat.com>
> >> ---
> >>  drivers/acpi/bus.c | 25 +++++++++++++++++++++++++
> >>  1 file changed, 25 insertions(+)
> >>
> >> diff --git a/drivers/acpi/bus.c b/drivers/acpi/bus.c
> >> index 95855cb..483d4d0 100644
> >> --- a/drivers/acpi/bus.c
> >> +++ b/drivers/acpi/bus.c
> >> @@ -109,11 +109,36 @@ acpi_status acpi_bus_get_status_handle(acpi_handle handle,
> >>  	return status;
> >>  }
> >>
> >> +/*
> >> + * Some ACPI devices are hidden (status == 0x0) in recent BIOS-es because
> >> + * some recent windows drivers bind to one device but poke at multiple
> >> + * devices at the same time, so the others get hidden.
> >> + * We work around this by always reporting ACPI_STA_DEFAULT for these
> >> + * devices. Note this MUST only be done for devices where this is safe.
> >> + */
> >> +static const struct acpi_device_id always_present_device_ids[] = {
> >> +	/*
> >> +	 * Cherrytrail pwm directly poked by GPU driver in win10,
> >> +	 * but Linux uses a separate pwm driver, harmless if not used.
> >> +	 */
> >> +	{ "80862288", },
> >> +	{ }
> >> +};
> >> +
> >>  int acpi_bus_get_status(struct acpi_device *device)
> >>  {
> >>  	acpi_status status;
> >>  	unsigned long long sta;
> >>
> >> +	/* acpi_match_device_ids checks status, so start with default */
> >> +	acpi_set_device_status(device, ACPI_STA_DEFAULT);
> >
> > This shouldn't be done in a "get" routine.
> 
> With this you mean the acpi_match_device_ids() check I assume ?
> (acpi_bus_get_status already calls acpi_set_device_status())
> 
> > Ideally, a scan handler should do that or similar.
> 
> The problem is that drivers/acpi/scan.c: acpi_bus_attach()
> calls acpi_bus_get_status() and if it does not set
> the status to present acpi_bus_attach() exits without bothering
> with attaching scan handlers, which is why I ended up doing this
> here.

Oh, this is interesting, please let me join to the party.

We've hit a similar problem, but for other one: namely, it's INT0002
that is found on a few CHT devices.  It's never bound properly by a
similar reason, where _STA is always zero on Linux:

            Method (_STA, 0, NotSerialized)  // _STA: Status
            {
                If (SOCS <= 0x04)
                {
                    Return (0x0F)
                }
                Else
                {
                    Return (Zero)
                }
            }

The device is supposed to be a "virtual GPIO" stuff, and the driver
hasn't been upstreamed from Intel.  Due to the lack of this driver
(and it's binding), the machine gets spurious IRQ#9 after the PM
resume, and it locks up at the second time of PM.


thanks,

Takashi