[PATCH v3] applesmc: Re-work SMC comms

Brad Campbell
2020-11-08T01:00:31Z

G'day Henrik,

I noticed you'd also loosened up the requirement for SMC_STATUS_BUSY in read_smc(). I assume
that causes problems on the early Macbook. This is revised on the one sent earlier.
If you could test this on your Air1,1 it'd be appreciated.

Commit fff2d0f701e6 ("hwmon: (applesmc) avoid overlong udelay()") introduced
an issue whereby communication with the SMC became unreliable with write
errors like :

[ 120.378614] applesmc: send_byte(0x00, 0x0300) fail: 0x40
[ 120.378621] applesmc: LKSB: write data fail
[ 120.512782] applesmc: send_byte(0x00, 0x0300) fail: 0x40
[ 120.512787] applesmc: LKSB: write data fail

The original code appeared to be timing sensitive and was not reliable with
the timing changes in the aforementioned commit.

This patch re-factors the SMC communication to remove the timing
dependencies and restore function with the changes previously committed.

Tested on : MacbookAir6,2 MacBookPro11,1 iMac12,2

Fixes: fff2d0f701e6 ("hwmon: (applesmc) avoid overlong udelay()")
Reported-by: Andreas Kemnade <andreas@kemnade.info>
Tested-by: Andreas Kemnade <andreas@kemnade.info> # MacBookAir6,2
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Brad Campbell <brad@fnarfbargle.com>
Signed-off-by: Henrik Rydberg <rydberg@bitmath.org>

---
Changelog :
v1 : Inital attempt
v2 : Address logic and coding style
v3 : Removed some debug hangover. Added tested-by. Modifications for MacBookAir1,1

diff --git a/drivers/hwmon/applesmc.c b/drivers/hwmon/applesmc.c
index a18887990f4a..3e968abb37aa 100644
--- a/drivers/hwmon/applesmc.c
+++ b/drivers/hwmon/applesmc.c
@@ -32,6 +32,7 @@
#include <linux/hwmon.h>
#include <linux/workqueue.h>
#include <linux/err.h>
+#include <linux/bits.h>

/* data port used by Apple SMC */
#define APPLESMC_DATA_PORT 0x300
@@ -42,6 +43,11 @@

#define APPLESMC_MAX_DATA_LENGTH 32

+/* Apple SMC status bits */
+#define SMC_STATUS_AWAITING_DATA BIT(0) /* SMC has data waiting */
+#define SMC_STATUS_IB_CLOSED BIT(1) /* Will ignore any input */
+#define SMC_STATUS_BUSY BIT(2) /* Command in progress */
+
/* wait up to 128 ms for a status change. */
#define APPLESMC_MIN_WAIT 0x0010
#define APPLESMC_RETRY_WAIT 0x0100
@@ -151,65 +157,73 @@ static unsigned int key_at_index;
static struct workqueue_struct *applesmc_led_wq;

/*
- * wait_read - Wait for a byte to appear on SMC port. Callers must
- * hold applesmc_lock.
+ * Wait for specific status bits with a mask on the SMC
+ * Used before and after writes, and before reads
*/
-static int wait_read(void)
+
+static int wait_status(u8 val, u8 mask)
{
unsigned long end = jiffies + (APPLESMC_MAX_WAIT * HZ) / USEC_PER_SEC;
u8 status;
int us;

+ udelay(APPLESMC_MIN_WAIT);
for (us = APPLESMC_MIN_WAIT; us < APPLESMC_MAX_WAIT; us <<= 1) {
- usleep_range(us, us * 16);
status = inb(APPLESMC_CMD_PORT);
- /* read: wait for smc to settle */
- if (status & 0x01)
+ if ((status & mask) == val)
return 0;
/* timeout: give up */
if (time_after(jiffies, end))
break;
+ usleep_range(us, us * 16);
}
-
- pr_warn("wait_read() fail: 0x%02x\n", status);
return -EIO;
}

/*
- * send_byte - Write to SMC port, retrying when necessary. Callers
+ * send_byte_data - Write to SMC data port. Callers
* must hold applesmc_lock.
+ * Parameter skip must be true on the last write of any
+ * command or it'll time out.
*/
-static int send_byte(u8 cmd, u16 port)
+
+static int send_byte_data(u8 cmd, u16 port, bool skip)
{
- u8 status;
- int us;
- unsigned long end = jiffies + (APPLESMC_MAX_WAIT * HZ) / USEC_PER_SEC;
+ int ret;

+ ret = wait_status(SMC_STATUS_BUSY, SMC_STATUS_BUSY | SMC_STATUS_IB_CLOSED);
+ if (ret)
+ return ret;
outb(cmd, port);
- for (us = APPLESMC_MIN_WAIT; us < APPLESMC_MAX_WAIT; us <<= 1) {
- usleep_range(us, us * 16);
- status = inb(APPLESMC_CMD_PORT);
- /* write: wait for smc to settle */
- if (status & 0x02)
- continue;
- /* ready: cmd accepted, return */
- if (status & 0x04)
- return 0;
- /* timeout: give up */
- if (time_after(jiffies, end))
- break;
- /* busy: long wait and resend */
- udelay(APPLESMC_RETRY_WAIT);
- outb(cmd, port);
- }
+ return wait_status(skip ? 0 : SMC_STATUS_BUSY, SMC_STATUS_BUSY);
+}

- pr_warn("send_byte(0x%02x, 0x%04x) fail: 0x%02x\n", cmd, port, status);
- return -EIO;
+static int send_byte(u8 cmd, u16 port)
+{
+ return send_byte_data(cmd, port, false);
}

+/*
+ * send_command - Write a command to the SMC. Callers must hold applesmc_lock.
+ * If SMC is in undefined state, any new command write resets the state machine.
+ */
+
static int send_command(u8 cmd)
{
- return send_byte(cmd, APPLESMC_CMD_PORT);
+ int ret;
+ int i;
+
+ for (i = 0; i < 16; i++) {
+ ret = wait_status(0, SMC_STATUS_IB_CLOSED);
+ if (ret)
+ return ret;
+
+ outb(cmd, APPLESMC_CMD_PORT);
+ ret = wait_status(SMC_STATUS_BUSY, SMC_STATUS_BUSY);
+ if (!ret)
+ return ret;
+ }
+ return -EIO;
}

static int send_argument(const char *key)
@@ -239,7 +253,8 @@ static int read_smc(u8 cmd, const char *key, u8 *buffer, u8 len)
}

for (i = 0; i < len; i++) {
- if (wait_read()) {
+ if (wait_status(SMC_STATUS_AWAITING_DATA,
+ SMC_STATUS_AWAITING_DATA | SMC_STATUS_IB_CLOSED)) {
pr_warn("%.4s: read data[%d] fail\n", key, i);
return -EIO;
}
@@ -250,7 +265,7 @@ static int read_smc(u8 cmd, const char *key, u8 *buffer, u8 len)
for (i = 0; i < 16; i++) {
udelay(APPLESMC_MIN_WAIT);
status = inb(APPLESMC_CMD_PORT);
- if (!(status & 0x01))
+ if (!(status & SMC_STATUS_AWAITING_DATA))
break;
data = inb(APPLESMC_DATA_PORT);
}
@@ -275,7 +290,7 @@ static int write_smc(u8 cmd, const char *key, const u8 *buffer, u8 len)
}

for (i = 0; i < len; i++) {
- if (send_byte(buffer[i], APPLESMC_DATA_PORT)) {
+ if (send_byte_data(buffer[i], APPLESMC_DATA_PORT, i == len - 1)) {
pr_warn("%s: write data fail\n", key);
return -EIO;
}