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authorHenrik Rydberg <rydberg@euromail.se>2013-10-02 19:15:03 +0200
committerBen Hutchings <ben@decadent.org.uk>2013-11-28 14:02:02 +0000
commit83e92c513be4e0c48cd4f6bc458b01a4bba86ce0 (patch)
tree38ee04396d93f10c2c59c3000222f25eeb2cd3a8
parent591c6cac8e8844d06e940774898c23f8684f5465 (diff)
hwmon: (applesmc) Always read until end of data
commit 25f2bd7f5add608c1d1405938f39c96927b275ca upstream. The crash reported and investigated in commit 5f4513 turned out to be caused by a change to the read interface on newer (2012) SMCs. Tests by Chris show that simply reading the data valid line is enough for the problem to go away. Additional tests show that the newer SMCs no longer wait for the number of requested bytes, but start sending data right away. Apparently the number of bytes to read is no longer specified as before, but instead found out by reading until end of data. Failure to read until end of data confuses the state machine, which eventually causes the crash. As a remedy, assuming bit0 is the read valid line, make sure there is nothing more to read before leaving the read function. Tested to resolve the original problem, and runtested on MBA3,1, MBP4,1, MBP8,2, MBP10,1, MBP10,2. The patch seems to have no effect on machines before 2012. Tested-by: Chris Murphy <chris@cmurf.com> Signed-off-by: Henrik Rydberg <rydberg@euromail.se> Signed-off-by: Guenter Roeck <linux@roeck-us.net> [bwh: Backported to 3.2: adjust context] Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
-rw-r--r--drivers/hwmon/applesmc.c13
1 files changed, 13 insertions, 0 deletions
diff --git a/drivers/hwmon/applesmc.c b/drivers/hwmon/applesmc.c
index 30cac58422b7..0b86d47e49ed 100644
--- a/drivers/hwmon/applesmc.c
+++ b/drivers/hwmon/applesmc.c
@@ -212,6 +212,7 @@ static int send_argument(const char *key)
static int read_smc(u8 cmd, const char *key, u8 *buffer, u8 len)
{
+ u8 status, data = 0;
int i;
if (send_command(cmd) || send_argument(key)) {
@@ -219,6 +220,7 @@ static int read_smc(u8 cmd, const char *key, u8 *buffer, u8 len)
return -EIO;
}
+ /* This has no effect on newer (2012) SMCs */
outb(len, APPLESMC_DATA_PORT);
for (i = 0; i < len; i++) {
@@ -229,6 +231,17 @@ static int read_smc(u8 cmd, const char *key, u8 *buffer, u8 len)
buffer[i] = inb(APPLESMC_DATA_PORT);
}
+ /* Read the data port until bit0 is cleared */
+ for (i = 0; i < 16; i++) {
+ udelay(APPLESMC_MIN_WAIT);
+ status = inb(APPLESMC_CMD_PORT);
+ if (!(status & 0x01))
+ break;
+ data = inb(APPLESMC_DATA_PORT);
+ }
+ if (i)
+ pr_warn("flushed %d bytes, last value is: %d\n", i, data);
+
return 0;
}