From patchwork Wed Jul  8 20:16:22 2009
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Date: Wed, 08 Jul 2009 22:16:22 +0200
From: Hector Martin <hector@marcansoft.com>
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To: Zhang Rui <rui.zhang@intel.com>
CC: Len Brown <lenb@kernel.org>, linux-acpi@vger.kernel.org
Subject: [PATCH] disable _BQC/_BCQ if it returns invalid values
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Validate the result of the _BQC or _BCQ method when querying the current
backlight level. If the value is out of range, the support for this
method is disabled. This does not break functionality as long as the
hardware doesn't touch the backlight level on it own, since the driver
will just use the last cached value.

Acer Aspire 8930G with BIOS v1.10 (latest) has this issue.

Signed-off-by: Hector Martin <hector@marcansoft.com>

--- linux-2.6.30/drivers/acpi/video.c	2009-07-08 22:04:54.000000000 +0200
+++ linux-2.6.30-mod/drivers/acpi/video.c	2009-07-08 22:12:19.000000000 +0200
@@ -602,15 +605,29 @@ acpi_video_device_lcd_get_level_current(
 						NULL, level);
 		if (ACPI_SUCCESS(status)) {
 			if (device->brightness->flags._BQC_use_index) {
+				if (*level >= (device->brightness->count - 2)) {
+					ACPI_WARNING((AE_INFO,
+						"%s is broken (returned %llu)",
+						buf, *level));
+					device->cap._BQC = device->cap._BCQ = 0;
+					*level = device->brightness->curr;
+					return 0;
+				}
 				if (device->brightness->flags._BCL_reversed)
 					*level = device->brightness->count
 								 - 3 - (*level);
 				*level = device->brightness->levels[*level + 2];
 
 			}
-			*level += bqc_offset_aml_bug_workaround;
-			device->brightness->curr = *level;
-			return 0;
+			if (*level > 100) {
+				ACPI_WARNING((AE_INFO, "%s is broken "
+					"(returned %llu)", buf, *level));
+				device->cap._BQC = device->cap._BCQ = 0;
+			} else {
+				*level += bqc_offset_aml_bug_workaround;
+				device->brightness->curr = *level;
+				return 0;
+			}
 		} else {
 			/* Fixme:
 			 * should we return an error or ignore this failure?