Re: [PATCH v4 3/4] ACPI / video: Do not register backlight if win8 and native interface exists

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

On Tuesday, October 08, 2013 02:40:00 PM Aaron Lu wrote:
> According to Matthew Garrett, "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 [8] 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".
> 
> So for Win8 systems, if there is native backlight control interface
> registered by GPU driver, ACPI video will not register its own. For
> users who prefer to keep ACPI video's backlight interface, the existing
> kernel cmdline option acpi_backlight=video can be used.
> 
> Signed-off-by: Aaron Lu <aaron.lu@intel.com>
> Tested-by: Igor Gnatenko <i.gnatenko.brain@gmail.com>
> Tested-by: Yves-Alexis Perez <corsac@debian.org>
> Tested-by: Mika Westerberg <mika.westerberg@linux.intel.com>
> ---
>  drivers/acpi/internal.h     |  5 ++---
>  drivers/acpi/video.c        | 10 +++++-----
>  drivers/acpi/video_detect.c | 14 ++++++++++++--
>  3 files changed, 19 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/acpi/internal.h b/drivers/acpi/internal.h
> index 20f4233..453ae8d 100644
> --- a/drivers/acpi/internal.h
> +++ b/drivers/acpi/internal.h
> @@ -169,9 +169,8 @@ int acpi_create_platform_device(struct acpi_device *adev,
>  					Video
>    -------------------------------------------------------------------------- */
>  #if defined(CONFIG_ACPI_VIDEO) || defined(CONFIG_ACPI_VIDEO_MODULE)
> -bool acpi_video_backlight_quirks(void);
> -#else
> -static inline bool acpi_video_backlight_quirks(void) { return false; }
> +bool acpi_osi_is_win8(void);
> +bool acpi_video_verify_backlight_support(void);
>  #endif
>  
>  #endif /* _ACPI_INTERNAL_H_ */
> diff --git a/drivers/acpi/video.c b/drivers/acpi/video.c
> index 3bd1eaa..343db59 100644
> --- a/drivers/acpi/video.c
> +++ b/drivers/acpi/video.c
> @@ -1256,8 +1256,8 @@ acpi_video_switch_brightness(struct acpi_video_device *device, int event)
>  	unsigned long long level_current, level_next;
>  	int result = -EINVAL;
>  
> -	/* no warning message if acpi_backlight=vendor is used */
> -	if (!acpi_video_backlight_support())
> +	/* no warning message if acpi_backlight=vendor or a quirk is used */
> +	if (!acpi_video_verify_backlight_support())
>  		return 0;
>  
>  	if (!device->brightness)
> @@ -1386,13 +1386,13 @@ acpi_video_bus_get_devices(struct acpi_video_bus *video,
>  static int acpi_video_bus_start_devices(struct acpi_video_bus *video)
>  {
>  	return acpi_video_bus_DOS(video, 0,
> -				  acpi_video_backlight_quirks() ? 1 : 0);
> +				  acpi_osi_is_win8() ? 1 : 0);
>  }
>  
>  static int acpi_video_bus_stop_devices(struct acpi_video_bus *video)
>  {
>  	return acpi_video_bus_DOS(video, 0,
> -				  acpi_video_backlight_quirks() ? 0 : 1);
> +				  acpi_osi_is_win8() ? 0 : 1);
>  }
>  
>  static void acpi_video_bus_notify(struct acpi_device *device, u32 event)
> @@ -1558,7 +1558,7 @@ acpi_video_bus_match(acpi_handle handle, u32 level, void *context,
>  
>  static void acpi_video_dev_register_backlight(struct acpi_video_device *device)
>  {
> -	if (acpi_video_backlight_support()) {
> +	if (acpi_video_verify_backlight_support()) {
>  		struct backlight_properties props;
>  		struct pci_dev *pdev;
>  		acpi_handle acpi_parent;
> diff --git a/drivers/acpi/video_detect.c b/drivers/acpi/video_detect.c
> index 940edbf..23d7d26 100644
> --- a/drivers/acpi/video_detect.c
> +++ b/drivers/acpi/video_detect.c
> @@ -37,6 +37,7 @@
>  #include <linux/acpi.h>
>  #include <linux/dmi.h>
>  #include <linux/pci.h>
> +#include <linux/backlight.h>
>  
>  #include "internal.h"
>  
> @@ -233,11 +234,11 @@ static void acpi_video_caps_check(void)
>  		acpi_video_get_capabilities(NULL);
>  }
>  
> -bool acpi_video_backlight_quirks(void)
> +bool acpi_osi_is_win8(void)
>  {
>  	return acpi_gbl_osi_data >= ACPI_OSI_WIN_8;
>  }
> -EXPORT_SYMBOL(acpi_video_backlight_quirks);
> +EXPORT_SYMBOL(acpi_osi_is_win8);
>  
>  /* Promote the vendor interface instead of the generic video module.
>   * This function allow DMI blacklists to be implemented by externals
> @@ -283,6 +284,15 @@ int acpi_video_backlight_support(void)
>  }
>  EXPORT_SYMBOL(acpi_video_backlight_support);
>  
> +bool acpi_video_verify_backlight_support(void)
> +{
> +	if (!(acpi_video_support & ACPI_VIDEO_BACKLIGHT_FORCE_VIDEO) &&
> +	    acpi_osi_is_win8() && backlight_device_registered(BACKLIGHT_RAW))
> +		return false;

If I'm not mistaken, this will introduce a regression for the people who have
problems with the native i915 backlight on Win8-compatible systems.  I'd prefer
to avoid that at this point.

> +	return acpi_video_backlight_support();
> +}
> +EXPORT_SYMBOL(acpi_video_verify_backlight_support);
> +
>  /*
>   * Use acpi_backlight=vendor/video to force that backlight switching
>   * is processed by vendor specific acpi drivers or video.ko driver.

Thanks!

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.