drm/i915: Check the LID device to decide whether the LVDS should be initialized

On some boxes the mobile chipset is used and there is no LVDS device. In such
case we had better not initialize the LVDS output device so that one pipe can
be used for other output device. For example: E-TOP.

But unfortunately the LVDS device is still initialized on the boxes based on
mobile chipset in KMS mode. It brings that this pipe occupied by LVDS can't be
used for other output device.

After checking the acpidump we find that there is no LID device on such boxes.
In such case we can use the LID device to decide whether the LVDS device should
be initialized.

If there is no LID device, we can think that there is no LVDS device. It is
unnecessary to initialize the LVDS output device.
If there exists the LID device, it will continue the current flowchart.

Maybe on some boxes there is no LVDS device but the LID device is found. In
such case it should be added to the quirk list.

http://bugs.freedesktop.org/show_bug.cgi?id=21496
http://bugs.freedesktop.org/show_bug.cgi?id=21856
http://bugs.freedesktop.org/show_bug.cgi?id=21127

Signed-off-by: Zhao Yakui <yakui.zhao@intel.com>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
[anholt: squashed in style fixups]
Signed-off-by: Eric Anholt <eric@anholt.net>

drivers/gpu/drm/i915/intel_lvds.c

@@ -36,6 +36,7 @@
 #include "intel_drv.h"
 #include "i915_drm.h"
 #include "i915_drv.h"
+#include <linux/acpi.h>
 
 #define I915_LVDS "i915_lvds"
 
@@ -788,6 +789,65 @@ static const struct dmi_system_id intel_no_lvds[] = {
 	{ }	/* terminating entry */
 };
 
+#ifdef CONFIG_ACPI
+/*
+ * check_lid_device -- check whether @handle is an ACPI LID device.
+ * @handle: ACPI device handle
+ * @level : depth in the ACPI namespace tree
+ * @context: the number of LID device when we find the device
+ * @rv: a return value to fill if desired (Not use)
+ */
+static acpi_status
+check_lid_device(acpi_handle handle, u32 level, void *context,
+			void **return_value)
+{
+	struct acpi_device *acpi_dev;
+	int *lid_present = context;
+
+	acpi_dev = NULL;
+	/* Get the acpi device for device handle */
+	if (acpi_bus_get_device(handle, &acpi_dev) || !acpi_dev) {
+		/* If there is no ACPI device for handle, return */
+		return AE_OK;
+	}
+
+	if (!strncmp(acpi_device_hid(acpi_dev), "PNP0C0D", 7))
+		*lid_present = 1;
+
+	return AE_OK;
+}
+
+/**
+ * check whether there exists the ACPI LID device by enumerating the ACPI
+ * device tree.
+ */
+static int intel_lid_present(void)
+{
+	int lid_present = 0;
+
+	if (acpi_disabled) {
+		/* If ACPI is disabled, there is no ACPI device tree to
+		 * check, so assume the LID device would have been present.
+		 */
+		return 1;
+	}
+
+	acpi_walk_namespace(ACPI_TYPE_DEVICE, ACPI_ROOT_OBJECT,
+				ACPI_UINT32_MAX,
+				check_lid_device, &lid_present, NULL);
+
+	return lid_present;
+}
+#else
+static int intel_lid_present(void)
+{
+	/* In the absence of ACPI built in, assume that the LID device would
+	 * have been present.
+	 */
+	return 1;
+}
+#endif
+
 /**
  * intel_lvds_init - setup LVDS connectors on this device
  * @dev: drm device
@@ -811,6 +871,16 @@ void intel_lvds_init(struct drm_device *dev)
 	if (dmi_check_system(intel_no_lvds))
 		return;
 
+	/* Assume that any device without an ACPI LID device also doesn't
+	 * have an integrated LVDS.  We would be better off parsing the BIOS
+	 * to get a reliable indicator, but that code isn't written yet.
+	 *
+	 * In the case of all-in-one desktops using LVDS that we've seen,
+	 * they're using SDVO LVDS.
+	 */
+	if (!intel_lid_present())
+		return;
+
 	if (IS_IGDNG(dev)) {
 		if ((I915_READ(PCH_LVDS) & LVDS_DETECTED) == 0)
 			return;