w1: omap-hdq: fix interrupt handling which did show spurious timeouts

Since

commit 27d13da8 ("w1: omap-hdq: Simplify driver with PM runtime autosuspend")

was applied,

I did see timeouts and wrong values when reading a bq27000 connected
to hdq of the omap3. This occurred mainly after boot but remained and
only sometimes settled down after several reads.

root@letux:~# time cat /sys/class/power_supply/bq27000-battery/uevent
POWER_SUPPLY_NAME=bq27000-battery
POWER_SUPPLY_STATUS=Discharging
POWER_SUPPLY_PRESENT=1
POWER_SUPPLY_VOLTAGE_NOW=0
POWER_SUPPLY_CURRENT_NOW=0
POWER_SUPPLY_CAPACITY=0
POWER_SUPPLY_CAPACITY_LEVEL=Normal
POWER_SUPPLY_TEMP=-2731
POWER_SUPPLY_TIME_TO_EMPTY_NOW=0
POWER_SUPPLY_TIME_TO_EMPTY_AVG=0
POWER_SUPPLY_TIME_TO_FULL_NOW=0
POWER_SUPPLY_TECHNOLOGY=Li-ion
POWER_SUPPLY_CHARGE_FULL=0
POWER_SUPPLY_CHARGE_NOW=0
POWER_SUPPLY_CHARGE_FULL_DESIGN=0
POWER_SUPPLY_CYCLE_COUNT=0
POWER_SUPPLY_ENERGY_NOW=0
POWER_SUPPLY_POWER_AVG=0
POWER_SUPPLY_HEALTH=Good
POWER_SUPPLY_MANUFACTURER=Texas Instruments

real    0m15.761s
user    0m0.001s
sys     0m0.025s
root@letux:~#

Sometimes the effect did disappear after accessing
the device multiple times, speed went up and results
became correct.

All this indicates that some interrupts from the hdq
controller are lost by the driver.

Enabling debugging revealed that there were spurious tx
and rx timeouts, i.e. the driver does not always recognise
interrupts. The main problem is that rx and tx interrupts
share a single variable which was sometimes reset to
0 wiping out other interrupts. And it was overwritten
by a second interrupt, independent of whether the
previous interrupt was already processed or not.

This patch improves interrupt handling to avoid such
races and loss of interrupt flags.

The ideas are:
* only the hdq_isr() sets bits in hdq_status
* it does not reset any bits
* it does wake_up() if any interrupt is pending
* bits are only reset by the read/write/break functions
  if they were waited for
* this makes sure that no interrupts can be lost
* rx/tx/timeout bits are completely decoupled from each
  other (and not reset all after waiting for any of them)
* which bits to reset is now specified by a new parameter
  to hdq_reset_irqstatus()
* hdq_reset_irqstatus() also returns the state before
  resetting so that we can encapsulate the spinlock
* this should now handle the case that the write and read
  are both already finished quickly before the hdq_write_byte()
  ends.
* Or that two interrupts occur in succession before
  they are processed by the driver.
  Old code may have reset all status bits making the next
  hdq_read_byte() timeout.
* the spinlock now always protects changing of bits in function
  hdq_reset_irqstatus() which could become a read-write-modify
  problem if the interrupt handler tries to read-modify-write
  exactly at the same moment
* we add mutex protection also for hdq_write_byte() just to
  be safe to not to disturb a hdq_read_byte() triggered by
  some other thread/process.

This patch was tested on a GTA04 and results in no
boot problems any more. And first read after boot is now ok:

root@letux:~# time cat /sys/class/power_supply/bq27000-battery/uevent
POWER_SUPPLY_NAME=bq27000-battery
POWER_SUPPLY_STATUS=Discharging
POWER_SUPPLY_PRESENT=1
POWER_SUPPLY_VOLTAGE_NOW=3970000
POWER_SUPPLY_CURRENT_NOW=354144
POWER_SUPPLY_CAPACITY=82
POWER_SUPPLY_CAPACITY_LEVEL=Normal
POWER_SUPPLY_TEMP=266
POWER_SUPPLY_TIME_TO_EMPTY_NOW=7680
POWER_SUPPLY_TIME_TO_EMPTY_AVG=7380
POWER_SUPPLY_TECHNOLOGY=Li-ion
POWER_SUPPLY_CHARGE_FULL=934856
POWER_SUPPLY_CHARGE_NOW=763976
POWER_SUPPLY_CHARGE_FULL_DESIGN=1233792
POWER_SUPPLY_CYCLE_COUNT=82
POWER_SUPPLY_ENERGY_NOW=2852840
POWER_SUPPLY_POWER_AVG=1392840
POWER_SUPPLY_HEALTH=Good
POWER_SUPPLY_MANUFACTURER=Texas Instruments

real    0m0.233s
user    0m0.000s
sys     0m0.025s
root@letux:~#

It was also tested with dev_dbg enabled and more
printk that all activities behave correctly, especially
hdq_write_byte(), hdq_read_byte(), omap_hdq_break().

Not tested is omap_w1_triplet().

Fixes: 27d13da8 ("w1: omap-hdq: Simplify driver with PM runtime autosuspend")
Cc: stable@vger.kernel.org # v5.6+
Signed-off-by: H. Nikolaus Schaller <hns@goldelico.com>
Link: https://lore.kernel.org/r/68fc8623ae741878beef049273696d2377526165.1590255176.git.hns@goldelico.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/w1/masters/omap_hdq.c

@@ -54,10 +54,10 @@ MODULE_PARM_DESC(w1_id, "1-wire id for the slave detection in HDQ mode");
 struct hdq_data {
 	struct device		*dev;
 	void __iomem		*hdq_base;
-	/* lock status update */
+	/* lock read/write/break operations */
 	struct  mutex		hdq_mutex;
+	/* interrupt status and a lock for it */
 	u8			hdq_irqstatus;
-	/* device lock */
 	spinlock_t		hdq_spinlock;
 	/* mode: 0-HDQ 1-W1 */
 	int                     mode;
@@ -120,13 +120,18 @@ static int hdq_wait_for_flag(struct hdq_data *hdq_data, u32 offset,
 }
 
 /* Clear saved irqstatus after using an interrupt */
-static void hdq_reset_irqstatus(struct hdq_data *hdq_data)
+static u8 hdq_reset_irqstatus(struct hdq_data *hdq_data, u8 bits)
 {
 	unsigned long irqflags;
+	u8 status;
 
 	spin_lock_irqsave(&hdq_data->hdq_spinlock, irqflags);
-	hdq_data->hdq_irqstatus = 0;
+	status = hdq_data->hdq_irqstatus;
+	/* this is a read-modify-write */
+	hdq_data->hdq_irqstatus &= ~bits;
 	spin_unlock_irqrestore(&hdq_data->hdq_spinlock, irqflags);
+
+	return status;
 }
 
 /* write out a byte and fill *status with HDQ_INT_STATUS */
@@ -135,6 +140,12 @@ static int hdq_write_byte(struct hdq_data *hdq_data, u8 val, u8 *status)
 	int ret;
 	u8 tmp_status;
 
+	ret = mutex_lock_interruptible(&hdq_data->hdq_mutex);
+	if (ret < 0) {
+		ret = -EINTR;
+		goto rtn;
+	}
+
 	*status = 0;
 
 	hdq_reg_out(hdq_data, OMAP_HDQ_TX_DATA, val);
@@ -144,14 +155,15 @@ static int hdq_write_byte(struct hdq_data *hdq_data, u8 val, u8 *status)
 		OMAP_HDQ_CTRL_STATUS_DIR | OMAP_HDQ_CTRL_STATUS_GO);
 	/* wait for the TXCOMPLETE bit */
 	ret = wait_event_timeout(hdq_wait_queue,
-		hdq_data->hdq_irqstatus, OMAP_HDQ_TIMEOUT);
+		(hdq_data->hdq_irqstatus & OMAP_HDQ_INT_STATUS_TXCOMPLETE),
+		OMAP_HDQ_TIMEOUT);
+	*status = hdq_reset_irqstatus(hdq_data, OMAP_HDQ_INT_STATUS_TXCOMPLETE);
 	if (ret == 0) {
 		dev_dbg(hdq_data->dev, "TX wait elapsed\n");
 		ret = -ETIMEDOUT;
 		goto out;
 	}
 
-	*status = hdq_data->hdq_irqstatus;
 	/* check irqstatus */
 	if (!(*status & OMAP_HDQ_INT_STATUS_TXCOMPLETE)) {
 		dev_dbg(hdq_data->dev, "timeout waiting for"
@@ -170,7 +182,8 @@ static int hdq_write_byte(struct hdq_data *hdq_data, u8 val, u8 *status)
 	}
 
 out:
-	hdq_reset_irqstatus(hdq_data);
+	mutex_unlock(&hdq_data->hdq_mutex);
+rtn:
 	return ret;
 }
 
@@ -181,7 +194,7 @@ static irqreturn_t hdq_isr(int irq, void *_hdq)
 	unsigned long irqflags;
 
 	spin_lock_irqsave(&hdq_data->hdq_spinlock, irqflags);
-	hdq_data->hdq_irqstatus = hdq_reg_in(hdq_data, OMAP_HDQ_INT_STATUS);
+	hdq_data->hdq_irqstatus |= hdq_reg_in(hdq_data, OMAP_HDQ_INT_STATUS);
 	spin_unlock_irqrestore(&hdq_data->hdq_spinlock, irqflags);
 	dev_dbg(hdq_data->dev, "hdq_isr: %x\n", hdq_data->hdq_irqstatus);
 
@@ -238,18 +251,19 @@ static int omap_hdq_break(struct hdq_data *hdq_data)
 
 	/* wait for the TIMEOUT bit */
 	ret = wait_event_timeout(hdq_wait_queue,
-		hdq_data->hdq_irqstatus, OMAP_HDQ_TIMEOUT);
+		(hdq_data->hdq_irqstatus & OMAP_HDQ_INT_STATUS_TIMEOUT),
+		OMAP_HDQ_TIMEOUT);
+	tmp_status = hdq_reset_irqstatus(hdq_data, OMAP_HDQ_INT_STATUS_TIMEOUT);
 	if (ret == 0) {
 		dev_dbg(hdq_data->dev, "break wait elapsed\n");
 		ret = -EINTR;
 		goto out;
 	}
 
-	tmp_status = hdq_data->hdq_irqstatus;
 	/* check irqstatus */
 	if (!(tmp_status & OMAP_HDQ_INT_STATUS_TIMEOUT)) {
 		dev_dbg(hdq_data->dev, "timeout waiting for TIMEOUT, %x\n",
-				tmp_status);
+			tmp_status);
 		ret = -ETIMEDOUT;
 		goto out;
 	}
@@ -278,7 +292,6 @@ static int omap_hdq_break(struct hdq_data *hdq_data)
 			" return to zero, %x\n", tmp_status);
 
 out:
-	hdq_reset_irqstatus(hdq_data);
 	mutex_unlock(&hdq_data->hdq_mutex);
 rtn:
 	return ret;
@@ -309,12 +322,15 @@ static int hdq_read_byte(struct hdq_data *hdq_data, u8 *val)
 		 */
 		wait_event_timeout(hdq_wait_queue,
 				   (hdq_data->hdq_irqstatus
-				    & OMAP_HDQ_INT_STATUS_RXCOMPLETE),
+				    & (OMAP_HDQ_INT_STATUS_RXCOMPLETE |
+				       OMAP_HDQ_INT_STATUS_TIMEOUT)),
 				   OMAP_HDQ_TIMEOUT);
-
+		status = hdq_reset_irqstatus(hdq_data,
+					     OMAP_HDQ_INT_STATUS_RXCOMPLETE |
+					     OMAP_HDQ_INT_STATUS_TIMEOUT);
 		hdq_reg_merge(hdq_data, OMAP_HDQ_CTRL_STATUS, 0,
 			OMAP_HDQ_CTRL_STATUS_DIR);
-		status = hdq_data->hdq_irqstatus;
+
 		/* check irqstatus */
 		if (!(status & OMAP_HDQ_INT_STATUS_RXCOMPLETE)) {
 			dev_dbg(hdq_data->dev, "timeout waiting for"
@@ -322,11 +338,12 @@ static int hdq_read_byte(struct hdq_data *hdq_data, u8 *val)
 			ret = -ETIMEDOUT;
 			goto out;
 		}
+	} else { /* interrupt had occurred before hdq_read_byte was called */
+		hdq_reset_irqstatus(hdq_data, OMAP_HDQ_INT_STATUS_RXCOMPLETE);
 	}
 	/* the data is ready. Read it in! */
 	*val = hdq_reg_in(hdq_data, OMAP_HDQ_RX_DATA);
 out:
-	hdq_reset_irqstatus(hdq_data);
 	mutex_unlock(&hdq_data->hdq_mutex);
 rtn:
 	return ret;
@@ -367,15 +384,15 @@ static u8 omap_w1_triplet(void *_hdq, u8 bdir)
 				 (hdq_data->hdq_irqstatus
 				  & OMAP_HDQ_INT_STATUS_RXCOMPLETE),
 				 OMAP_HDQ_TIMEOUT);
+	/* Must clear irqstatus for another RXCOMPLETE interrupt */
+	hdq_reset_irqstatus(hdq_data, OMAP_HDQ_INT_STATUS_RXCOMPLETE);
+
 	if (err == 0) {
 		dev_dbg(hdq_data->dev, "RX wait elapsed\n");
 		goto out;
 	}
 	id_bit = (hdq_reg_in(_hdq, OMAP_HDQ_RX_DATA) & 0x01);
 
-	/* Must clear irqstatus for another RXCOMPLETE interrupt */
-	hdq_reset_irqstatus(hdq_data);
-
 	/* read comp_bit */
 	hdq_reg_merge(_hdq, OMAP_HDQ_CTRL_STATUS,
 		      ctrl | OMAP_HDQ_CTRL_STATUS_DIR, mask);
@@ -383,6 +400,9 @@ static u8 omap_w1_triplet(void *_hdq, u8 bdir)
 				 (hdq_data->hdq_irqstatus
 				  & OMAP_HDQ_INT_STATUS_RXCOMPLETE),
 				 OMAP_HDQ_TIMEOUT);
+	/* Must clear irqstatus for another RXCOMPLETE interrupt */
+	hdq_reset_irqstatus(hdq_data, OMAP_HDQ_INT_STATUS_RXCOMPLETE);
+
 	if (err == 0) {
 		dev_dbg(hdq_data->dev, "RX wait elapsed\n");
 		goto out;
@@ -409,6 +429,9 @@ static u8 omap_w1_triplet(void *_hdq, u8 bdir)
 				 (hdq_data->hdq_irqstatus
 				  & OMAP_HDQ_INT_STATUS_TXCOMPLETE),
 				 OMAP_HDQ_TIMEOUT);
+	/* Must clear irqstatus for another TXCOMPLETE interrupt */
+	hdq_reset_irqstatus(hdq_data, OMAP_HDQ_INT_STATUS_TXCOMPLETE);
+
 	if (err == 0) {
 		dev_dbg(hdq_data->dev, "TX wait elapsed\n");
 		goto out;
@@ -418,7 +441,6 @@ static u8 omap_w1_triplet(void *_hdq, u8 bdir)
 		      OMAP_HDQ_CTRL_STATUS_SINGLE);
 
 out:
-	hdq_reset_irqstatus(hdq_data);
 	mutex_unlock(&hdq_data->hdq_mutex);
 rtn:
 	pm_runtime_mark_last_busy(hdq_data->dev);