Re: [PATCH v3] applesmc: Re-work SMC comms

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Hi Brad,

On 2020-11-08 02:00, Brad Campbell wrote:
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.

No, I managed to screw up the patch; you can see that I carefully added the same treatment for the read argument, being unsure if the BUSY state would remain during the AVAILABLE data phase. I can check that again, but unfortunately the patch in this email shows the same problem.

I think it may be worthwhile to rethink the behavior of wait_status() here. If one machine shows no change after a certain status bit change, then perhaps the others share that behavior, and we are waiting in vain. Just imagine how many years of cpu that is, combined. ;-)

Henrik


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@xxxxxxxxxxxx>
Tested-by: Andreas Kemnade <andreas@xxxxxxxxxxxx> # MacBookAir6,2
Acked-by: Arnd Bergmann <arnd@xxxxxxxx>
Signed-off-by: Brad Campbell <brad@xxxxxxxxxxxxxxx>
Signed-off-by: Henrik Rydberg <rydberg@xxxxxxxxxxx>

---
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;
  		}





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