hwmon: (applesmc) Re-work SMC comms

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>
Link: https://lore.kernel.org/r/194a7d71-a781-765a-d177-c962ef296b90@fnarfbargle.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

diff --git a/drivers/hwmon/applesmc.c b/drivers/hwmon/applesmc.c
index a188879..79b498f 100644 (file)
--- 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
@@ -42,10 +43,13 @@
 
 #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 */
+
+/* Initial wait is 8us */
+#define APPLESMC_MIN_WAIT      0x0008
 
 #define APPLESMC_READ_CMD      0x10
 #define APPLESMC_WRITE_CMD     0x11
@@ -151,65 +155,84 @@ 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.
+ * This does 10 fast loops of 8us then exponentially backs off for a
+ * minimum total wait of 262ms. Depending on usleep_range this could
+ * run out past 500ms.
  */
-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;
+       int i;
 
-       for (us = APPLESMC_MIN_WAIT; us < APPLESMC_MAX_WAIT; us <<= 1) {
-               usleep_range(us, us * 16);
+       us = APPLESMC_MIN_WAIT;
+       for (i = 0; i < 24 ; i++) {
                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 * 2);
+               if (i > 9)
+                       us <<= 1;
        }
-
-       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;
+       /*
+        * This needs to be a separate read looking for bit 0x04
+        * after bit 0x02 falls. If consolidated with the wait above
+        * this extra read may not happen if status returns both
+        * simultaneously and this would appear to be required.
+        */
+       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;
+       return wait_status(0, SMC_STATUS_BUSY);
 }
 
 static int send_argument(const char *key)
@@ -226,6 +249,11 @@ static int read_smc(u8 cmd, const char *key, u8 *buffer, u8 len)
 {
        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 +267,8 @@ 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_BUSY,
+                               SMC_STATUS_AWAITING_DATA | SMC_STATUS_BUSY)) {
                        pr_warn("%.4s: read data[%d] fail\n", key, i);
                        return -EIO;
                }
@@ -250,19 +279,24 @@ 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);
        }
        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 +315,7 @@ static int write_smc(u8 cmd, const char *key, const u8 *buffer, u8 len)
                }
        }
 
-       return 0;
+       return wait_status(0, SMC_STATUS_BUSY);
 }
 
 static int read_register_count(unsigned int *count)