[PATCH v4 1/1] applesmc: Re-work SMC comms

Brad Campbell
2020-11-11T03:40:06Z

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, MacBookAir1,1,
MacBookAir3,1

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 : Initial attempt
v2 : Address logic and coding style
v3 : Removed some debug hangover. Added tested-by. Modifications for MacBookAir1,1
v4 : Re-factored logic based on Apple driver. Simplified wait_status loop
Index: linux-stable/drivers/hwmon/applesmc.c
===================================================================
--- linux-stable.orig/drivers/hwmon/applesmc.c
+++ linux-stable/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
@@ -42,10 +43,14 @@

#define APPLESMC_MAX_DATA_LENGTH 32

-/* wait up to 128 ms for a status change. */
-#define APPLESMC_MIN_WAIT 0x0010
-#define APPLESMC_RETRY_WAIT 0x0100
-#define APPLESMC_MAX_WAIT 0x20000
+/* Apple SMC status bits */
+#define SMC_STATUS_AWAITING_DATA BIT(0) /* SMC has data waiting to be read */
+#define SMC_STATUS_IB_CLOSED BIT(1) /* Will ignore any input */
+#define SMC_STATUS_BUSY BIT(2) /* Command in progress */
+
+/* Exponential delay boundaries */
+#define APPLESMC_MIN_WAIT 0x0008
+#define APPLESMC_MAX_WAIT 0x100000

#define APPLESMC_READ_CMD 0x10
#define APPLESMC_WRITE_CMD 0x11
@@ -151,65 +156,73 @@ 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 all transactions
*/
-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;

- for (us = APPLESMC_MIN_WAIT; us < APPLESMC_MAX_WAIT; us <<= 1) {
- usleep_range(us, us * 16);
+ for (us = APPLESMC_MIN_WAIT; us <= APPLESMC_MAX_WAIT; us <<= 1) {
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(APPLESMC_MIN_WAIT, us);
}
-
- pr_warn("wait_read() fail: 0x%02x\n", status);
return -EIO;
}

-/*
- * send_byte - Write to SMC port, retrying when necessary. Callers
- * must hold applesmc_lock.
- */
+/* send_byte - Write to SMC data port. Callers must hold applesmc_lock. */
+
static int send_byte(u8 cmd, u16 port)
{
- u8 status;
- int us;
- unsigned long end = jiffies + (APPLESMC_MAX_WAIT * HZ) / USEC_PER_SEC;
+ int status;

+ status = wait_status(0, SMC_STATUS_IB_CLOSED);
+ if (status)
+ return status;
+ status = wait_status(SMC_STATUS_BUSY, SMC_STATUS_BUSY);
+ if (status)
+ return status;
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);
- }
-
- pr_warn("send_byte(0x%02x, 0x%04x) fail: 0x%02x\n", cmd, port, status);
- return -EIO;
+ return 0;
}

+/* send_command - Write a command to the SMC. Callers must hold applesmc_lock. */
+
static int send_command(u8 cmd)
{
- return send_byte(cmd, APPLESMC_CMD_PORT);
+ int ret;
+
+ ret = wait_status(0, SMC_STATUS_IB_CLOSED);
+ if (ret)
+ return ret;
+ outb(cmd, APPLESMC_CMD_PORT);
+ return 0;
+}
+
+/* Based on logic from the Apple driver. This is issued before any interaction
+ * If busy is stuck high, issue a read command to reset the SMC state
+ * machine. If busy is stuck high after the command then the SMC is
+ * jammed.
+ */
+
+static int smc_sane(void)
+{
+ int ret;
+
+ ret = wait_status(0, SMC_STATUS_BUSY);
+ if (!ret)
+ return ret;
+ ret = send_command(APPLESMC_READ_CMD);
+ if (ret)
+ return ret;
+ ret = wait_status(0, SMC_STATUS_BUSY);
+ if (!ret)
+ return ret;
+ return -EIO;
}

static int send_argument(const char *key)
@@ -226,6 +239,11 @@ static int read_smc(u8 cmd, const char *
{
u8 status, data = 0;
int i;
+ int ret;
+
+ ret = smc_sane();
+ if (ret)
+ return ret;

if (send_command(cmd) || send_argument(key)) {
pr_warn("%.4s: read arg fail\n", key);
@@ -239,7 +257,8 @@ static int read_smc(u8 cmd, const char *
}

for (i = 0; i < len; i++) {
- if (wait_read()) {
+ if (wait_status(SMC_STATUS_AWAITING_DATA | SMC_STATUS_BUSY,
+ SMC_STATUS_AWAITING_DATA | SMC_STATUS_BUSY) < 0) {
pr_warn("%.4s: read data[%d] fail\n", key, i);
return -EIO;
}
@@ -250,19 +269,24 @@ static int read_smc(u8 cmd, const char *
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);
}
if (i)
pr_warn("flushed %d bytes, last value is: %d\n", i, data);

- return 0;
+ return wait_status(0, SMC_STATUS_BUSY);
}

static int write_smc(u8 cmd, const char *key, const u8 *buffer, u8 len)
{
int i;
+ int ret;
+
+ ret = smc_sane();
+ if (ret)
+ return ret;

if (send_command(cmd) || send_argument(key)) {
pr_warn("%s: write arg fail\n", key);
@@ -281,7 +305,7 @@ static int write_smc(u8 cmd, const char
}
}

- return 0;
+ return wait_status(0, SMC_STATUS_BUSY);
}

static int read_register_count(unsigned int *count)