From 83e92c513be4e0c48cd4f6bc458b01a4bba86ce0 Mon Sep 17 00:00:00 2001 From: Henrik Rydberg Date: Wed, 2 Oct 2013 19:15:03 +0200 Subject: 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 Signed-off-by: Henrik Rydberg Signed-off-by: Guenter Roeck [bwh: Backported to 3.2: adjust context] Signed-off-by: Ben Hutchings --- drivers/hwmon/applesmc.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) 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; } -- cgit v1.2.3