CHROMIUM: Input: atmel_mxt_ts - allow writing to object sysfs entry

Userspace can write a 32-bit value (encoded as a 8 character hex string)
to the 'object' sysfs entry to modify a single byte of the object table.
The hex string encodes 4 bytes, in the following format:

 TTIIFFVV

Where:
 TT = object type (atmel 'T' number)
 II = object instance (0-indexes, so 0 is the first instance)
 FF = object offset
 VV = byte value

The object table is modified in device ram, which means the change is
volatile, and will be overwritten on the next device reset.  To make
changes permanent, the new settings should be persisted in the device's
Non-Voltatile Memory using the updatenv sysfs entry.

Also, since the device driver initializes itself by reading some values
from the object table, the entire driver may need to be unloaded and
reloaded after writing the values for the driver to stay in sync.  Whether
this is required depends on exactly which values were updated.

Signed-off-by: Daniel Kurtz <djkurtz@chromium.org>
BUG=chromium-os:27713
TEST=ls -l /sys/.../object
  --wr--r--r 1 root root 4096 Feb 14 20:54 update_fw

  (0) confirm current number of fingers (look for (Type 9, Offset 14)):
  $ cat /sys/.../object
  (1) Change number of reported fingers (Type: 0x09, Offset: 0x0e) to 7:
  $ echo -n "090e07" > /sys/.../object
  (2) confirm current number of fingers (look for (Type 9, Offset 14)):
  $ cat /sys/.../object
  (3) using mtplot, notice that there now up to 7 fingers are reported.
  (4) reboot, and verify that the old number of fingers is restored.
TEST=Trying to write to a non-existant instance, or past the length of
     an object, should fail.  For example:
   echo -n "070005ab" > /sys/bus/i2c/devices/<dev>/object
  => -bash: echo: write error: Invalid argument

Change-Id: I8149770f762a84ef457c7bf4aefdb310d07c52c5
Reviewed-on: https://gerrit.chromium.org/gerrit/17944
Commit-Ready: Daniel Kurtz <djkurtz@chromium.org>
Reviewed-by: Daniel Kurtz <djkurtz@chromium.org>
Tested-by: Daniel Kurtz <djkurtz@chromium.org>

diff --git a/drivers/input/touchscreen/atmel_mxt_ts.c b/drivers/input/touchscreen/atmel_mxt_ts.c
index 2405ba1..e810e0f 100644 (file)
--- a/drivers/input/touchscreen/atmel_mxt_ts.c
+++ b/drivers/input/touchscreen/atmel_mxt_ts.c
@@ -956,6 +956,35 @@ static ssize_t mxt_object_show(struct device *dev,
        return count;
 }
 
+static ssize_t mxt_object_store(struct device *dev,
+                               struct device_attribute *attr,
+                               const char *buf, size_t count)
+{
+       struct mxt_data *data = dev_get_drvdata(dev);
+       int ret;
+       u32 param;
+       u8 type, instance, offset, val;
+
+       ret = kstrtou32(buf, 16, &param);
+       if (ret < 0)
+               return -EINVAL;
+
+       /*
+        * Byte Write Command is encoded in 32-bit word: TTIIOOVV:
+        * <Type> <Instance> <Offset> <Value>
+        */
+       type = (param & 0xff000000) >> 24;
+       instance = (param & 0x00ff0000) >> 16;
+       offset = (param & 0x0000ff00) >> 8;
+       val = param & 0x000000ff;
+
+       ret = mxt_write_object(data, type, instance, offset, val);
+       if (ret)
+               return ret;
+
+       return count;
+}
+
 static int mxt_load_fw(struct device *dev, const char *fn)
 {
        struct mxt_data *data = dev_get_drvdata(dev);
@@ -1061,7 +1090,8 @@ static ssize_t mxt_update_fw_store(struct device *dev,
        return count;
 }
 
-static DEVICE_ATTR(object, S_IRUGO, mxt_object_show, NULL);
+static DEVICE_ATTR(object, S_IRUGO | S_IWUSR, mxt_object_show,
+                  mxt_object_store);
 static DEVICE_ATTR(update_fw, S_IWUSR, NULL, mxt_update_fw_store);
 
 static struct attribute *mxt_attrs[] = {