Re: [PATCH 3/3] i915: Don't provide ACPI backlight interface if firmware expects Windows 8

["Rafael J. Wysocki" <rjw@sisk.pl>]

On Friday, July 05, 2013 10:00:55 PM Rafael J. Wysocki wrote:
> On Friday, July 05, 2013 02:20:14 PM Rafael J. Wysocki wrote:
> > On Sunday, June 09, 2013 07:01:39 PM Matthew Garrett wrote:
> > > Windows 8 leaves backlight control up to individual graphics drivers rather
> > > than making ACPI calls itself. There's plenty of evidence to suggest that
> > > the Intel driver for Windows doesn't use the ACPI interface, including the
> > > fact that it's broken on a bunch of machines when the OS claims to support
> > > Windows 8. The simplest thing to do appears to be to disable the ACPI
> > > backlight interface on these systems.
> > > 
> > > Signed-off-by: Matthew Garrett <matthew.garrett@nebula.com>
> > > ---
> > >  drivers/gpu/drm/i915/i915_dma.c | 3 +++
> > >  1 file changed, 3 insertions(+)
> > > 
> > > diff --git a/drivers/gpu/drm/i915/i915_dma.c b/drivers/gpu/drm/i915/i915_dma.c
> > > index 3b315ba..23b6292 100644
> > > --- a/drivers/gpu/drm/i915/i915_dma.c
> > > +++ b/drivers/gpu/drm/i915/i915_dma.c
> > > @@ -1661,6 +1661,9 @@ int i915_driver_load(struct drm_device *dev, unsigned long flags)
> > >  		/* Must be done after probing outputs */
> > >  		intel_opregion_init(dev);
> > >  		acpi_video_register();
> > > +		/* Don't use ACPI backlight functions on Windows 8 platforms */
> > > +		if (acpi_osi_version() >= ACPI_OSI_WIN_8)
> > > +			acpi_video_backlight_unregister();
> > >  	}
> > >  
> > >  	if (IS_GEN5(dev))
> > > 
> > 
> > Well, this causes build failures to happen when the ACPI video driver is
> > modular and the graphics driver is not.
> > 
> > I'm not sure how to resolve that, so suggestions are welcome.
> 
> Actually, that happened with the radeon patch.
> 
> That said, ACPI_OSI_WIN_8 doesn't make much sense for !CONFIG_ACPI, for
> example.
> 
> What about making acpi_video_register() do the quirk instead?  We could add an
> argument to it indicating whether or not quirks should be applied.

Actually, I wonder what about the appended patch (on top of the Aaron's
https://patchwork.kernel.org/patch/2812951/) instead of [1-3/3] from this series.

Thanks,
Rafael


---
 drivers/acpi/video_detect.c |   11 +++++++++--
 include/linux/acpi.h        |    1 +
 2 files changed, 10 insertions(+), 2 deletions(-)

Index: linux-pm/drivers/acpi/video_detect.c
===================================================================
--- linux-pm.orig/drivers/acpi/video_detect.c
+++ linux-pm/drivers/acpi/video_detect.c
@@ -203,6 +203,9 @@ long acpi_video_get_capabilities(acpi_ha
 		 */
 
 		dmi_check_system(video_detect_dmi_table);
+
+		if (acpi_gbl_osi_data >= ACPI_OSI_WIN_8)
+			acpi_video_support |= ACPI_VIDEO_FORCE_NO_BACKLIGHT;
 	} else {
 		status = acpi_bus_get_device(graphics_handle, &tmp_dev);
 		if (ACPI_FAILURE(status)) {
@@ -258,13 +261,17 @@ int acpi_video_backlight_support(void)
 {
 	acpi_video_caps_check();
 
-	/* First check for boot param -> highest prio */
+	/* First, check if no backlight support has been forced upon us. */
+	if (acpi_video_support & ACPI_VIDEO_FORCE_NO_BACKLIGHT)
+		return 0;
+
+	/* Next check for boot param -> second highest prio */
 	if (acpi_video_support & ACPI_VIDEO_BACKLIGHT_FORCE_VENDOR)
 		return 0;
 	else if (acpi_video_support & ACPI_VIDEO_BACKLIGHT_FORCE_VIDEO)
 		return 1;
 
-	/* Then check for DMI blacklist -> second highest prio */
+	/* Then check for DMI blacklist -> third highest prio */
 	if (acpi_video_support & ACPI_VIDEO_BACKLIGHT_DMI_VENDOR)
 		return 0;
 	else if (acpi_video_support & ACPI_VIDEO_BACKLIGHT_DMI_VIDEO)
Index: linux-pm/include/linux/acpi.h
===================================================================
--- linux-pm.orig/include/linux/acpi.h
+++ linux-pm/include/linux/acpi.h
@@ -191,6 +191,7 @@ extern bool wmi_has_guid(const char *gui
 #define ACPI_VIDEO_BACKLIGHT_DMI_VIDEO			0x0200
 #define ACPI_VIDEO_OUTPUT_SWITCHING_DMI_VENDOR		0x0400
 #define ACPI_VIDEO_OUTPUT_SWITCHING_DMI_VIDEO		0x0800
+#define ACPI_VIDEO_FORCE_NO_BACKLIGHT			0x1000
 
 #if defined(CONFIG_ACPI_VIDEO) || defined(CONFIG_ACPI_VIDEO_MODULE)