From patchwork Tue Apr 17 16:23:50 2018

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Subject: ACPI / video: Only default only_lcd to true on Win8-ready _desktops_

From: Hans de Goede <hdegoede@redhat.com>

X-Patchwork-Id: 10345845

Message-Id: <20180417162350.12227-1-hdegoede@redhat.com>

To: "Rafael J . Wysocki" <rjw@rjwysocki.net>, Len Brown <lenb@kernel.org>

Cc: Hans de Goede <hdegoede@redhat.com>,

 Zhang Rui <rui.zhang@intel.com>, linux-acpi@vger.kernel.org,

 James Hogan <jhogan@kernel.org>

Date: Tue, 17 Apr 2018 18:23:50 +0200

Commit 5928c281524f ("ACPI / video: Default lcd_only to true on Win8-ready

and newer machines") made only_lcd default to true on all machines where

acpi_osi_is_win8() returns true, including laptops.

The purpose of this is to avoid the bogus / non-working acpi backlight

interface which many newer BIOS-es define on desktop machines.

But this is causing a regression on some laptops, specifically on the

Dell XPS 13 2013 model, which does not have the LCD flag set for its

fully functional ACPI backlight interface.

Rather then DMI quirking our way out of this, this commits changes the

logic for setting only_lcd to true, to only do this on machines with

a desktop (or server) dmi chassis-type.

Note that we cannot simply only check the chassis-type and not register

the backlight interface based on that as there are some laptops and

tablets which have their chassis-type set to "3" aka desktop. Hopefully

the combination of checking the LCD flag, but only on devices with

a desktop(ish) chassis-type will avoid the needs for DMI quirks for this,

or at least limit the amount of DMI quirks which we need to a minimum.

Cc: James Hogan <jhogan@kernel.org>

Reported-and-tested-by: James Hogan <jhogan@kernel.org>

Signed-off-by: Hans de Goede <hdegoede@redhat.com>

---

 drivers/acpi/acpi_video.c | 27 +++++++++++++++++++++++++--

 1 file changed, 25 insertions(+), 2 deletions(-)

diff --git a/drivers/acpi/acpi_video.c b/drivers/acpi/acpi_video.c

index 76fb96966f7b..2f2e737be0f8 100644

--- a/drivers/acpi/acpi_video.c

+++ b/drivers/acpi/acpi_video.c

@@ -2123,6 +2123,25 @@ static int __init intel_opregion_present(void)

 	return opregion;

 }

+static bool dmi_is_desktop(void)

+{

+	const char *chassis_type;

+

+	chassis_type = dmi_get_system_info(DMI_CHASSIS_TYPE);

+	if (!chassis_type)

+		return false;

+

+	if (!strcmp(chassis_type, "3") || /*  3: Desktop */

+	    !strcmp(chassis_type, "4") || /*  4: Low Profile Desktop */

+	    !strcmp(chassis_type, "5") || /*  5: Pizza Box */

+	    !strcmp(chassis_type, "6") || /*  6: Mini Tower */

+	    !strcmp(chassis_type, "7") || /*  7: Tower */

+	    !strcmp(chassis_type, "11"))  /* 11: Main Server Chassis */

+		return true;

+

+	return false;

+}

+

 int acpi_video_register(void)

 {

 	int ret = 0;

@@ -2143,8 +2162,12 @@ int acpi_video_register(void)

 	 * win8 ready (where we also prefer the native backlight driver, so

 	 * normally the acpi_video code should not register there anyways).

 	 */

-	if (only_lcd == -1)

-		only_lcd = acpi_osi_is_win8();

+	if (only_lcd == -1) {

+		if (dmi_is_desktop() && acpi_osi_is_win8())

+			only_lcd = true;

+		else

+			only_lcd = false;

+	}

 	dmi_check_system(video_dmi_table);