[PATCH 5/6] platform/x86: ideapad-laptop: Expose camera_power only if supported

["Eray Orçunus" <erayorcunus@gmail.com>]

IdeaPads dropped support for VPCCMD_W_CAMERA somewhere between 2014-2016,
none of the IdeaPads produced after that I tested supports it. Fortunately
I found a way to check it; if the DSDT has camera device(s) defined, it
shouldn't have working VPCCMD_W_CAMERA, thus camera_power shouldn't be
exposed to sysfs. To accomplish this, walk the ACPI namespace in
ideapad_check_features and check the devices starting with "CAM".
Tested on 520-15IKB and Legion Y520, which successfully didn't expose
the camera_power attribute.

Link: https://www.spinics.net/lists/platform-driver-x86/msg26147.html
Signed-off-by: Eray Orçunus <erayorcunus@gmail.com>
---
 drivers/platform/x86/ideapad-laptop.c | 53 ++++++++++++++++++++++++++-
 1 file changed, 52 insertions(+), 1 deletion(-)

diff --git a/drivers/platform/x86/ideapad-laptop.c b/drivers/platform/x86/ideapad-laptop.c
index f3d4f2beda07..65eea2e65bbe 100644
--- a/drivers/platform/x86/ideapad-laptop.c
+++ b/drivers/platform/x86/ideapad-laptop.c
@@ -149,6 +149,7 @@ struct ideapad_private {
 		bool fn_lock              : 1;
 		bool hw_rfkill_switch     : 1;
 		bool kbd_bl               : 1;
+		bool cam_ctrl_via_ec      : 1;
 		bool touchpad_ctrl_via_ec : 1;
 		bool usb_charging         : 1;
 	} features;
@@ -163,6 +164,26 @@ static bool no_bt_rfkill;
 module_param(no_bt_rfkill, bool, 0444);
 MODULE_PARM_DESC(no_bt_rfkill, "No rfkill for bluetooth.");
 
+static char *cam_device_prefix = "CAM";
+
+static acpi_status acpi_find_device_callback(acpi_handle handle, u32 level,
+					     void *context, void **return_value)
+{
+	char buffer[8];
+	struct acpi_buffer ret_buf;
+
+	ret_buf.length = sizeof(buffer);
+	ret_buf.pointer = buffer;
+
+	if (ACPI_SUCCESS(acpi_get_name(handle, ACPI_SINGLE_NAME, &ret_buf)))
+		if (strncmp(ret_buf.pointer, context, strlen(context)) == 0) {
+			*return_value = handle;
+			return AE_CTRL_TERMINATE;
+		}
+
+	return AE_OK;
+}
+
 /*
  * ACPI Helpers
  */
@@ -675,7 +696,7 @@ static umode_t ideapad_is_visible(struct kobject *kobj,
 	bool supported = true;
 
 	if (attr == &dev_attr_camera_power.attr)
-		supported = test_bit(CFG_CAP_CAM_BIT, &priv->cfg);
+		supported = priv->features.cam_ctrl_via_ec;
 	else if (attr == &dev_attr_conservation_mode.attr)
 		supported = priv->features.conservation_mode;
 	else if (attr == &dev_attr_fan_mode.attr)
@@ -1523,10 +1544,40 @@ static const struct dmi_system_id hw_rfkill_list[] = {
 static void ideapad_check_features(struct ideapad_private *priv)
 {
 	acpi_handle handle = priv->adev->handle;
+	acpi_handle pci_handle;
+	acpi_handle temp_handle = NULL;
 	unsigned long val;
+	acpi_status status;
 
 	priv->features.hw_rfkill_switch = dmi_check_system(hw_rfkill_list);
 
+	/*
+	 * Some IdeaPads have camera switch via EC (mostly older ones),
+	 * some don't. Fortunately we know that if DSDT contains device
+	 * object for the camera, camera isn't switchable via EC.
+	 * So, let's walk the namespace and try to find CAM* object.
+	 * If we can't find it, set cam_ctrl_via_ec to true.
+	 */
+
+	priv->features.cam_ctrl_via_ec = false;
+
+	if (test_bit(CFG_CAP_CAM_BIT, &priv->cfg)) {
+		status = acpi_get_handle(handle, "^^^", &pci_handle);
+		if (ACPI_SUCCESS(status)) {
+			status = acpi_walk_namespace(ACPI_TYPE_DEVICE, pci_handle,
+						     ACPI_UINT32_MAX,
+						     acpi_find_device_callback,
+						     NULL, cam_device_prefix,
+						     &temp_handle);
+
+			if (ACPI_SUCCESS(status) && temp_handle == NULL)
+				priv->features.cam_ctrl_via_ec = true;
+
+		} else
+			dev_warn(&priv->platform_device->dev,
+				"Could not find PCI* node in the namespace\n");
+	}
+
 	/* Most ideapads with ELAN0634 touchpad don't use EC touchpad switch */
 	priv->features.touchpad_ctrl_via_ec = !acpi_dev_present("ELAN0634", NULL, -1);
 
-- 
2.34.1