ACPI: thinkpad-acpi: fix brightness dimming control bug

ibm-acpi and thinkpad-acpi did not know about bit 5 of the EC backlight
level control register (EC 0x31), so it was always forced to zero on
any writes.

This would disable the BIOS option to *not* use a dimmer backlight level
scale while on battery, and who knows what else (there are two other
control bits of unknown function).

Bit 5 controls the "reduce backlight levels when on battery" optional
functionality (active low).  Bits 6 and 7 are better left alone as well,
instead of being forced to zero.

Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Signed-off-by: Len Brown <len.brown@intel.com>

1 files changed, 49 insertions, 15 deletions

diff --git a/drivers/misc/thinkpad_acpi.c b/drivers/misc/thinkpad_acpi.c
index 7dc6b73e8f5b..5e25abc54008 100644
--- a/drivers/misc/thinkpad_acpi.c
+++ b/drivers/misc/thinkpad_acpi.c
@@ -4295,8 +4295,16 @@ static struct ibm_struct ecdump_driver_data = {
 
 #define TPACPI_BACKLIGHT_DEV_NAME "thinkpad_screen"
 
+enum {
+        TP_EC_BACKLIGHT = 0x31,
+
+        /* TP_EC_BACKLIGHT bitmasks */
+        TP_EC_BACKLIGHT_LVLMSK = 0x1F,
+        TP_EC_BACKLIGHT_CMDMSK = 0xE0,
+        TP_EC_BACKLIGHT_MAPSW = 0x20,
+};
+
 static struct backlight_device *ibm_backlight_device;
-static int brightness_offset = 0x31;
 static int brightness_mode;
 static unsigned int brightness_enable = 2; /* 2 = auto, 0 = no, 1 = yes */
 
@@ -4305,16 +4313,24 @@ static struct mutex brightness_mutex;
 /*
  * ThinkPads can read brightness from two places: EC 0x31, or
  * CMOS NVRAM byte 0x5E, bits 0-3.
+ *
+ * EC 0x31 has the following layout
+ *   Bit 7: unknown function
+ *   Bit 6: unknown function
+ *   Bit 5: Z: honour scale changes, NZ: ignore scale changes
+ *   Bit 4: must be set to zero to avoid problems
+ *   Bit 3-0: backlight brightness level
+ *
+ * brightness_get_raw returns status data in the EC 0x31 layout
  */
-static int brightness_get(struct backlight_device *bd)
+static int brightness_get_raw(int *status)
 {
         u8 lec = 0, lcmos = 0, level = 0;
 
         if (brightness_mode & 1) {
-                if (!acpi_ec_read(brightness_offset, &lec))
+                if (!acpi_ec_read(TP_EC_BACKLIGHT, &lec))
                         return -EIO;
-                lec &= (tp_features.bright_16levels)? 0x0f : 0x07;
-                level = lec;
+                level = lec & TP_EC_BACKLIGHT_LVLMSK;
         };
         if (brightness_mode & 2) {
                 lcmos = (nvram_read_byte(TP_NVRAM_ADDR_BRIGHTNESS)
@@ -4325,6 +4341,8 @@ static int brightness_get(struct backlight_device *bd)
         }
 
         if (brightness_mode == 3) {
+                *status = lec;  /* Prefer EC, CMOS is just a backing store */
+                lec &= TP_EC_BACKLIGHT_LVLMSK;
                 if (lec == lcmos)
                         tp_warned.bright_cmos_ec_unsync = 0;
                 else {
@@ -4338,9 +4356,11 @@ static int brightness_get(struct backlight_device *bd)
                         }
                         return -EIO;
                 }
+        } else {
+                *status = level;
         }
 
-        return level;
+        return 0;
 }
 
 /* May return EINTR which can always be mapped to ERESTARTSYS */
@@ -4348,19 +4368,22 @@ static int brightness_set(int value)
 {
         int cmos_cmd, inc, i, res;
         int current_value;
+        int command_bits;
 
-        if (value > ((tp_features.bright_16levels)? 15 : 7))
+        if (value > ((tp_features.bright_16levels)? 15 : 7) ||
+            value < 0)
                 return -EINVAL;
 
         res = mutex_lock_interruptible(&brightness_mutex);
         if (res < 0)
                 return res;
 
-        current_value = brightness_get(NULL);
-        if (current_value < 0) {
-                res = current_value;
+        res = brightness_get_raw(&current_value);
+        if (res < 0)
                 goto errout;
-        }
+
+        command_bits = current_value & TP_EC_BACKLIGHT_CMDMSK;
+        current_value &= TP_EC_BACKLIGHT_LVLMSK;
 
         cmos_cmd = value > current_value ?
                         TP_CMOS_BRIGHTNESS_UP :
@@ -4375,7 +4398,8 @@ static int brightness_set(int value)
                         goto errout;
                 }
                 if ((brightness_mode & 1) &&
-                    !acpi_ec_write(brightness_offset, i + inc)) {
+                    !acpi_ec_write(TP_EC_BACKLIGHT,
+                                   (i + inc) | command_bits)) {
                         res = -EIO;
                         goto errout;;
                 }
@@ -4398,6 +4422,17 @@ static int brightness_update_status(struct backlight_device *bd)
                                 bd->props.brightness : 0);
 }
 
+static int brightness_get(struct backlight_device *bd)
+{
+        int status, res;
+
+        res = brightness_get_raw(&status);
+        if (res < 0)
+                return 0; /* FIXME: teach backlight about error handling */
+
+        return status & TP_EC_BACKLIGHT_LVLMSK;
+}
+
 static struct backlight_ops ibm_backlight_data = {
         .get_brightness = brightness_get,
         .update_status  = brightness_update_status,
@@ -4462,8 +4497,7 @@ static int __init brightness_init(struct ibm_init_struct *iibm)
         if (brightness_mode > 3)
                 return -EINVAL;
 
-        b = brightness_get(NULL);
-        if (b < 0)
+        if (brightness_get_raw(&b) < 0)
                 return 1;
 
         if (tp_features.bright_16levels)
@@ -4481,7 +4515,7 @@ static int __init brightness_init(struct ibm_init_struct *iibm)
 
         ibm_backlight_device->props.max_brightness =
                                 (tp_features.bright_16levels)? 15 : 7;
-        ibm_backlight_device->props.brightness = b;
+        ibm_backlight_device->props.brightness = b & TP_EC_BACKLIGHT_LVLMSK;
         backlight_update_status(ibm_backlight_device);
 
         return 0;