IB/ipath: Lock and always use shadow copies of GPIO register

The new LED blinking interface adds more contention for the
unprotected GPIO pins that were already shared, though not commonly at
the same time.  We add locks to the accesses to these pins so that
Read-Modify-Write is now safe.  Some of these locks are added at
interrupt context, so we shadow the registers which drive and inspect
these pins to avoid the mmio read/writes.  This mitigates the effects
of the locks and hastens us through the interrupt.

Add locking and always use shadows for registers controlling GPIO pins
(ExtCtrl and GPIOout). The use of shadows implies doing less I/O,
which can make I2C operation too fast on some platforms. An explicit
udelay(1) in SCL manipulation fixes that.

Signed-off-by: Michael Albaugh <michael.albaugh@qlogic.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>

1 files changed, 40 insertions, 28 deletions

diff --git a/drivers/infiniband/hw/ipath/ipath_eeprom.c b/drivers/infiniband/hw/ipath/ipath_eeprom.c
index 030185f90ee2..26daac9d8b63 100644
--- a/drivers/infiniband/hw/ipath/ipath_eeprom.c
+++ b/drivers/infiniband/hw/ipath/ipath_eeprom.c
@@ -95,39 +95,37 @@ static int i2c_gpio_set(struct ipath_devdata *dd,
 			enum i2c_type line,
 			enum i2c_state new_line_state)
 {
-	u64 read_val, write_val, mask, *gpioval;
+	u64 out_mask, dir_mask, *gpioval;
+	unsigned long flags = 0;
 
 	gpioval = &dd->ipath_gpio_out;
-	read_val = ipath_read_kreg64(dd, dd->ipath_kregs->kr_extctrl);
-	if (line == i2c_line_scl)
-		mask = dd->ipath_gpio_scl;
-	else
-		mask = dd->ipath_gpio_sda;
 
-	if (new_line_state == i2c_line_high)
+	if (line == i2c_line_scl) {
+		dir_mask = dd->ipath_gpio_scl;
+		out_mask = (1UL << dd->ipath_gpio_scl_num);
+	} else {
+		dir_mask = dd->ipath_gpio_sda;
+		out_mask = (1UL << dd->ipath_gpio_sda_num);
+	}
+
+	spin_lock_irqsave(&dd->ipath_gpio_lock, flags);
+	if (new_line_state == i2c_line_high) {
 		/* tri-state the output rather than force high */
-		write_val = read_val & ~mask;
-	else
+		dd->ipath_extctrl &= ~dir_mask;
+	} else {
 		/* config line to be an output */
-		write_val = read_val | mask;
-	ipath_write_kreg(dd, dd->ipath_kregs->kr_extctrl, write_val);
+		dd->ipath_extctrl |= dir_mask;
+	}
+	ipath_write_kreg(dd, dd->ipath_kregs->kr_extctrl, dd->ipath_extctrl);
 
-	/* set high and verify */
+	/* set output as well (no real verify) */
 	if (new_line_state == i2c_line_high)
-		write_val = 0x1UL;
+		*gpioval |= out_mask;
 	else
-		write_val = 0x0UL;
+		*gpioval &= ~out_mask;
 
-	if (line == i2c_line_scl) {
-		write_val <<= dd->ipath_gpio_scl_num;
-		*gpioval = *gpioval & ~(1UL << dd->ipath_gpio_scl_num);
-		*gpioval |= write_val;
-	} else {
-		write_val <<= dd->ipath_gpio_sda_num;
-		*gpioval = *gpioval & ~(1UL << dd->ipath_gpio_sda_num);
-		*gpioval |= write_val;
-	}
 	ipath_write_kreg(dd, dd->ipath_kregs->kr_gpio_out, *gpioval);
+	spin_unlock_irqrestore(&dd->ipath_gpio_lock, flags);
 
 	return 0;
 }
@@ -145,8 +143,9 @@ static int i2c_gpio_get(struct ipath_devdata *dd,
 			enum i2c_type line,
 			enum i2c_state *curr_statep)
 {
-	u64 read_val, write_val, mask;
+	u64 read_val, mask;
 	int ret;
+	unsigned long flags = 0;
 
 	/* check args */
 	if (curr_statep == NULL) {
@@ -154,15 +153,21 @@ static int i2c_gpio_get(struct ipath_devdata *dd,
 		goto bail;
 	}
 
-	read_val = ipath_read_kreg64(dd, dd->ipath_kregs->kr_extctrl);
 	/* config line to be an input */
 	if (line == i2c_line_scl)
 		mask = dd->ipath_gpio_scl;
 	else
 		mask = dd->ipath_gpio_sda;
-	write_val = read_val & ~mask;
-	ipath_write_kreg(dd, dd->ipath_kregs->kr_extctrl, write_val);
+
+	spin_lock_irqsave(&dd->ipath_gpio_lock, flags);
+	dd->ipath_extctrl &= ~mask;
+	ipath_write_kreg(dd, dd->ipath_kregs->kr_extctrl, dd->ipath_extctrl);
+	/*
+	 * Below is very unlikely to reflect true input state if Output
+	 * Enable actually changed.
+	 */
 	read_val = ipath_read_kreg64(dd, dd->ipath_kregs->kr_extstatus);
+	spin_unlock_irqrestore(&dd->ipath_gpio_lock, flags);
 
 	if (read_val & mask)
 		*curr_statep = i2c_line_high;
@@ -192,6 +197,7 @@ static void i2c_wait_for_writes(struct ipath_devdata *dd)
 
 static void scl_out(struct ipath_devdata *dd, u8 bit)
 {
+	udelay(1);
 	i2c_gpio_set(dd, i2c_line_scl, bit ? i2c_line_high : i2c_line_low);
 
 	i2c_wait_for_writes(dd);
@@ -314,12 +320,18 @@ static int eeprom_reset(struct ipath_devdata *dd)
 	int clock_cycles_left = 9;
 	u64 *gpioval = &dd->ipath_gpio_out;
 	int ret;
+	unsigned long flags;
 
-	eeprom_init = 1;
+	spin_lock_irqsave(&dd->ipath_gpio_lock, flags);
+	/* Make sure shadows are consistent */
+	dd->ipath_extctrl = ipath_read_kreg64(dd, dd->ipath_kregs->kr_extctrl);
 	*gpioval = ipath_read_kreg64(dd, dd->ipath_kregs->kr_gpio_out);
+	spin_unlock_irqrestore(&dd->ipath_gpio_lock, flags);
+
 	ipath_cdbg(VERBOSE, "Resetting i2c eeprom; initial gpioout reg "
 		   "is %llx\n", (unsigned long long) *gpioval);
 
+	eeprom_init = 1;
 	/*
 	 * This is to get the i2c into a known state, by first going low,
 	 * then tristate sda (and then tristate scl as first thing