[Intel-gfx] [PATCH v6 1/3] ACPI / bus: Introduce a list of ids for "always present" devices

[Lukas Wunner]

On Wed, Apr 19, 2017 at 12:28:50PM +0200, Rafael J. Wysocki wrote:
> On Wed, Apr 19, 2017 at 10:59 AM, Hans de Goede <hdegoede at redhat.com> wrote:
> > On 18-04-17 15:34, Rafael J. Wysocki wrote:
> >> On Tue, Apr 18, 2017 at 1:54 PM, Hans de Goede <hdegoede at redhat.com> wrote:
> >>>
> >>> Several Cherry Trail 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 Cherry Trail 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      | 65
> >>> +++++++++++++++++++++++++++++++++++++++++++++++++
> >>>  include/acpi/acpi_bus.h |  6 +----
> >>>  2 files changed, 66 insertions(+), 5 deletions(-)
> >>>
> >>> diff --git a/drivers/acpi/bus.c b/drivers/acpi/bus.c
> >>> index 34fbe02..eb30630 100644
> >>> --- a/drivers/acpi/bus.c
> >>> +++ b/drivers/acpi/bus.c
> >>> @@ -34,6 +34,8 @@
> >>>  #include <linux/reboot.h>
> >>>  #include <linux/delay.h>
> >>>  #ifdef CONFIG_X86
> >>> +#include <asm/cpu_device_id.h>
> >>> +#include <asm/intel-family.h>
> >>>  #include <asm/mpspec.h>
> >>>  #endif
> >>>  #include <linux/acpi_iort.h>
> >>> @@ -132,6 +134,69 @@ int acpi_bus_get_status(struct acpi_device *device)
> >>>  }
> >>>  EXPORT_SYMBOL(acpi_bus_get_status);
> >>>
> >>> +#ifdef CONFIG_X86
> >>> +/*
> >>> + * 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.
> >>> + *
> >>> + * This forcing of devices to be present is limited to specific CPU
> >>> (SoC)
> >>> + * models both to avoid potentially causing trouble on other models and
> >>> + * because some HIDs are re-used on different SoCs for completely
> >>> + * different devices.
> >>> + */
> >>> +struct always_present_device_id {
> >>> +       struct acpi_device_id hid[2];
> >>> +       struct x86_cpu_id cpu_ids[2];
> >>
> >> This really is x86-specific, so it should go into somewhere like
> >> arch/x86/kernel/acpi/ or drivers/acpi/x86/ (not present yet).
> >
> > Ok, but then how do you want to hook this up, before you said
> > that you wanted to deal with this in acpi_set_device_status(),
> > which belongs in drivers/acpi/bus.c, do you want the x86
> > code to provide something like a
> >
> > bool acpi_device_always_present(struct acpi_device *adev) {
> > }
> >
> > Helper function and use that in the drivers/acpi/bus.c
> > acpi_set_device_status() implementation ?
> 
> Yes, something like that.
> 
> In a header file you can make it depend on CONFIG_X86 and provide and
> empty static inline stub for the "not defined" case.

The PCI subsystem uses __weak stubs such as pcibios_add_bus() for arch-
specific behaviour, or quirks which can be declared in arch/x86 to
constrain them to this specific platform.

Perhaps it makes sense to introduce ACPI quirks which can be declared
the same way as PCI quirks to avoid cluttering the generic code with
arch- or device-specific special cases.  So in this case we'd have
something like:

DECLARE_ACPI_FIXUP_STATUS(const char *hid, const char *uid, hook);

And before calling _STA we'd check for presence of a fixup for the
device in question.  Any additional stuff such as _HRV, CPU ID,
DMI data could be checked in the fixup hook.  Thoughts?

By the way:

> >>> +void acpi_set_device_status(struct acpi_device *adev, u32 sta)
> >>> +{
> >>> +       u32 *status = (u32 *)&adev->status;
> >>> +#ifdef CONFIG_X86
> >>> +       u32 old_status = *status;
> >>> +       int i;
> >>> +
> >>> +       /* acpi_match_device_ids checks status, so start with default */
> >>> +       *status = ACPI_STA_DEFAULT;
> >>> +       for (i = 0; i < ARRAY_SIZE(always_present_device_ids); i++) {
> >>> +               if (acpi_match_device_ids(adev,
> >>> +                       always_present_device_ids[i].hid) == 0 &&
> >>> +                   adev->pnp.unique_id &&
> >>> +                   strcmp(adev->pnp.unique_id,
> >>> +                          always_present_device_ids[i].uid) == 0 &&
> >>> +                   x86_match_cpu(always_present_device_ids[i].cpu_ids))
> >>> {

Why is this added to acpi_set_device_status(), rather than
acpi_bus_get_status_handle() ?  That way you're gratuitously calling
_STA even though you ignore its return value afterwards.

Thanks,

Lukas