[PATCH] applesmc: add sysfs file to report OSK

["Gabriel L. Somlo" <somlo@cmu.edu>]

The AppleSMC contains two char[32] keys, OSK0 and OSK1, which are not
reported in the key count and index by default. These keys are used by
the OS X boot sequence, and normally don't matter when running Linux.

This patch creates a sysfs entry which reports the value of these keys
as an ASCII string, to help emulators (such as QEMU) load OS X when
running on genuine Apple hardware.

Signed-off-by: Gabriel L. Somlo <somlo@cmu.edu>
---

For extra context: To boot OS X as a guest, QEMU must (among others)
emulate the AppleSMC. To boot successfully, OS X insists on querying
the (emulated) SMC for the value of OSK0 and OSK1. Currently, these
values must be supplied on the QEMU command line as

  -device applesmc,osk="...concatenated values of OSK0 and OSK1..."

With the availability of /sys/devices/platform/applesmc.768/osk, the
emulated QEMU AppleSMC could acquire this string directly from the
(Apple-manufactured) host machine.

Thanks,
  Gabriel

 drivers/hwmon/applesmc.c |   18 ++++++++++++++++++
 1 files changed, 18 insertions(+), 0 deletions(-)

diff --git a/drivers/hwmon/applesmc.c b/drivers/hwmon/applesmc.c
index b41baff..0c7cc71 100644
--- a/drivers/hwmon/applesmc.c
+++ b/drivers/hwmon/applesmc.c
@@ -1013,6 +1013,23 @@ static ssize_t applesmc_key_at_index_store(struct device *dev,
 	return count;
 }
 
+static ssize_t applesmc_osk_show(struct device *dev,
+				struct device_attribute *attr, char *sysfsbuf)
+{
+	int fail;
+
+	mutex_lock(&smcreg.mutex);
+	fail = read_smc(APPLESMC_READ_CMD, "OSK0", sysfsbuf, 32) ||
+	       read_smc(APPLESMC_READ_CMD, "OSK1", sysfsbuf + 32, 32);
+	mutex_unlock(&smcreg.mutex);
+	if (fail)
+		return -1;
+
+	sysfsbuf[64] = '\n';
+	sysfsbuf[65] = '\0';
+	return 65;
+}
+
 static struct led_classdev applesmc_backlight = {
 	.name			= "smc::kbd_backlight",
 	.default_trigger	= "nand-disk",
@@ -1027,6 +1044,7 @@ static struct applesmc_node_group info_group[] = {
 	{ "key_at_index_type", applesmc_key_at_index_type_show },
 	{ "key_at_index_data_length", applesmc_key_at_index_data_length_show },
 	{ "key_at_index_data", applesmc_key_at_index_read_show },
+	{ "osk", applesmc_osk_show },
 	{ }
 };
 
-- 
1.7.7.6