ACPI: thinkpad-acpi: allow use of CMOS NVRAM for brightness control

It appears that Lenovo decided to break the EC brightness control interface
in a weird way in their latest BIOSes.  Fortunately, the old CMOS NVRAM
interface works just fine in such BIOSes.

Add a module parameter that allows the user to select which strategy to use
for brightness control: EC, NVRAM, or both.  By default, do both (which is
the way thinkpad-acpi used to work until now) on IBM ThinkPads, and use
NVRAM only on Lenovo ThinkPads.

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

1 files changed, 53 insertions, 9 deletions

diff --git a/drivers/misc/thinkpad_acpi.c b/drivers/misc/thinkpad_acpi.c
index 99500af651c1..5318eb272c61 100644
--- a/drivers/misc/thinkpad_acpi.c
+++ b/drivers/misc/thinkpad_acpi.c
@@ -2953,9 +2953,22 @@ static int __init brightness_init(struct ibm_init_struct *iibm)
 
         vdbg_printk(TPACPI_DBG_INIT, "initializing brightness subdriver\n");
 
+        if (!brightness_mode) {
+                if (thinkpad_id.vendor == PCI_VENDOR_ID_LENOVO)
+                        brightness_mode = 2;
+                else
+                        brightness_mode = 3;
+
+                dbg_printk(TPACPI_DBG_INIT, "selected brightness_mode=%d\n",
+                        brightness_mode);
+        }
+
+        if (brightness_mode > 3)
+                return -EINVAL;
+
         b = brightness_get(NULL);
         if (b < 0)
-                return b;
+                return 1;
 
         ibm_backlight_device = backlight_device_register(
                                         TPACPI_BACKLIGHT_DEV_NAME, NULL, NULL,
@@ -2991,13 +3004,35 @@ static int brightness_update_status(struct backlight_device *bd)
                                 bd->props.brightness : 0);
 }
 
+/*
+ * ThinkPads can read brightness from two places: EC 0x31, or
+ * CMOS NVRAM byte 0x5E, bits 0-3.
+ */
 static int brightness_get(struct backlight_device *bd)
 {
-        u8 level;
-        if (!acpi_ec_read(brightness_offset, &level))
-                return -EIO;
+        u8 lec = 0, lcmos = 0, level = 0;
 
-        level &= 0x7;
+        if (brightness_mode & 1) {
+                if (!acpi_ec_read(brightness_offset, &lec))
+                        return -EIO;
+                lec &= 7;
+                level = lec;
+        };
+        if (brightness_mode & 2) {
+                lcmos = (nvram_read_byte(TP_NVRAM_ADDR_BRIGHTNESS)
+                         & TP_NVRAM_MASK_LEVEL_BRIGHTNESS)
+                        >> TP_NVRAM_POS_LEVEL_BRIGHTNESS;
+                level = lcmos;
+        }
+
+        if (brightness_mode == 3 && lec != lcmos) {
+                printk(IBM_ERR
+                        "CMOS NVRAM (%u) and EC (%u) do not agree "
+                        "on display brightness level\n",
+                        (unsigned int) lcmos,
+                        (unsigned int) lec);
+                return -EIO;
+        }
 
         return level;
 }
@@ -3007,14 +3042,20 @@ static int brightness_set(int value)
         int cmos_cmd, inc, i;
         int current_value = brightness_get(NULL);
 
-        value &= 7;
+        if (value > 7)
+                return -EINVAL;
 
-        cmos_cmd = value > current_value ? TP_CMOS_BRIGHTNESS_UP : TP_CMOS_BRIGHTNESS_DOWN;
+        cmos_cmd = value > current_value ?
+                        TP_CMOS_BRIGHTNESS_UP :
+                        TP_CMOS_BRIGHTNESS_DOWN;
         inc = value > current_value ? 1 : -1;
+
         for (i = current_value; i != value; i += inc) {
-                if (issue_thinkpad_cmos_command(cmos_cmd))
+                if ((brightness_mode & 2) &&
+                    issue_thinkpad_cmos_command(cmos_cmd))
                         return -EIO;
-                if (!acpi_ec_write(brightness_offset, i + inc))
+                if ((brightness_mode & 1) &&
+                    !acpi_ec_write(brightness_offset, i + inc))
                         return -EIO;
         }
 
@@ -4485,6 +4526,9 @@ module_param(force_load, bool, 0);
 static int fan_control_allowed;
 module_param_named(fan_control, fan_control_allowed, bool, 0);
 
+static int brightness_mode;
+module_param_named(brightness_mode, brightness_mode, int, 0);
+
 #define IBM_PARAM(feature) \
         module_param_call(feature, set_ibm_param, NULL, NULL, 0)