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From:   "Rafael J. Wysocki" <rjw@rjwysocki.net>
To:     Linux ACPI <linux-acpi@vger.kernel.org>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        Linux PM <linux-pm@vger.kernel.org>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Mika Westerberg <mika.westerberg@linux.intel.com>,
        Hans de Goede <hdegoede@redhat.com>,
        Sakari Ailus <sakari.ailus@linux.intel.com>,
        Henrique de Moraes Holschuh <hmh@hmh.eng.br>,
        Mark Gross <markgross@kernel.org>,
        ibm-acpi-devel@lists.sourceforge.net,
        platform-driver-x86@vger.kernel.org
Subject: [PATCH v2 12/16] platform/x86/thinkpad_acpi: Use acpi_dev_for_each_child()
Date:   Mon, 13 Jun 2022 20:30:19 +0200
Message-ID: <2091400.OBFZWjSADL@kreacher>
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From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Instead of walking the list of children of an ACPI device directly,
use acpi_dev_for_each_child() to carry out an action for all of
the given ACPI device's children.

This will help to eliminate the children list head from struct
acpi_device as it is redundant and it is used in questionable ways
in some places (in particular, locking is needed for walking the
list pointed to it safely, but it is often missing).

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---

v1 -> v2:
   * Eliminate unnecessary branch (Andy).

---
 drivers/platform/x86/thinkpad_acpi.c |   53 +++++++++++++++++------------------
 1 file changed, 27 insertions(+), 26 deletions(-)

Index: linux-pm/drivers/platform/x86/thinkpad_acpi.c
===================================================================
--- linux-pm.orig/drivers/platform/x86/thinkpad_acpi.c
+++ linux-pm/drivers/platform/x86/thinkpad_acpi.c
@@ -6841,6 +6841,31 @@ static const struct backlight_ops ibm_ba
 
 /* --------------------------------------------------------------------- */
 
+static int __init tpacpi_evaluate_bcl(struct acpi_device *adev, void *not_used)
+{
+	struct acpi_buffer buffer = { ACPI_ALLOCATE_BUFFER, NULL };
+	union acpi_object *obj;
+	acpi_status status;
+	int rc;
+
+	status = acpi_evaluate_object(adev->handle, "_BCL", NULL, &buffer);
+	if (ACPI_FAILURE(status))
+		return 0;
+
+	obj = buffer.pointer;
+	if (!obj || obj->type != ACPI_TYPE_PACKAGE) {
+		acpi_handle_info(adev->handle,
+				 "Unknown _BCL data, please report this to %s\n",
+				 TPACPI_MAIL);
+		rc = 0;
+	} else {
+		rc = obj->package.count;
+	}
+	kfree(obj);
+
+	return rc;
+}
+
 /*
  * Call _BCL method of video device.  On some ThinkPads this will
  * switch the firmware to the ACPI brightness control mode.
@@ -6848,37 +6873,13 @@ static const struct backlight_ops ibm_ba
 
 static int __init tpacpi_query_bcl_levels(acpi_handle handle)
 {
-	struct acpi_buffer buffer = { ACPI_ALLOCATE_BUFFER, NULL };
-	union acpi_object *obj;
-	struct acpi_device *device, *child;
-	int rc;
+	struct acpi_device *device;
 
 	device = acpi_fetch_acpi_dev(handle);
 	if (!device)
 		return 0;
 
-	rc = 0;
-	list_for_each_entry(child, &device->children, node) {
-		acpi_status status = acpi_evaluate_object(child->handle, "_BCL",
-							  NULL, &buffer);
-		if (ACPI_FAILURE(status)) {
-			buffer.length = ACPI_ALLOCATE_BUFFER;
-			continue;
-		}
-
-		obj = (union acpi_object *)buffer.pointer;
-		if (!obj || (obj->type != ACPI_TYPE_PACKAGE)) {
-			pr_err("Unknown _BCL data, please report this to %s\n",
-				TPACPI_MAIL);
-			rc = 0;
-		} else {
-			rc = obj->package.count;
-		}
-		break;
-	}
-
-	kfree(buffer.pointer);
-	return rc;
+	return acpi_dev_for_each_child(device, tpacpi_evaluate_bcl, NULL);
 }