[PATCH 6.1,6.2,6.3 v3 1/6] counter: 104-quad-8: Fix race condition between FLAG and CNTR reads

[PATCH 6.1,6.2,6.3 v3 1/6] counter: 104-quad-8: Fix race condition between FLAG and CNTR reads

[William Breathitt Gray]

The Counter (CNTR) register is 24 bits wide, but we can have an
effective 25-bit count value by setting bit 24 to the XOR of the Borrow
flag and Carry flag. The flags can be read from the FLAG register, but a
race condition exists: the Borrow flag and Carry flag are instantaneous
and could change by the time the count value is read from the CNTR
register.

Since the race condition could result in an incorrect 25-bit count
value, remove support for 25-bit count values from this driver;
hard-coded maximum count values are replaced by a LS7267_CNTR_MAX define
for consistency and clarity.

Fixes: 28e5d3bb0325 ("iio: 104-quad-8: Add IIO support for the ACCES 104-QUAD-8")
Cc: <stable@vger.kernel.org> # 6.1.x
Cc: <stable@vger.kernel.org> # 6.2.x
Signed-off-by: William Breathitt Gray <william.gray@linaro.org>
---
Changes in v3:
 - Initialize *val in quad8_count_read()

 drivers/counter/104-quad-8.c | 29 ++++++++---------------------
 1 file changed, 8 insertions(+), 21 deletions(-)

diff --git a/drivers/counter/104-quad-8.c b/drivers/counter/104-quad-8.c
index deed4afadb29..d59e4f34a680 100644
--- a/drivers/counter/104-quad-8.c
+++ b/drivers/counter/104-quad-8.c
@@ -97,10 +97,6 @@ struct quad8 {
 	struct quad8_reg __iomem *reg;
 };
 
-/* Borrow Toggle flip-flop */
-#define QUAD8_FLAG_BT BIT(0)
-/* Carry Toggle flip-flop */
-#define QUAD8_FLAG_CT BIT(1)
 /* Error flag */
 #define QUAD8_FLAG_E BIT(4)
 /* Up/Down flag */
@@ -133,6 +129,9 @@ struct quad8 {
 #define QUAD8_CMR_QUADRATURE_X2 0x10
 #define QUAD8_CMR_QUADRATURE_X4 0x18
 
+/* Each Counter is 24 bits wide */
+#define LS7267_CNTR_MAX GENMASK(23, 0)
+
 static int quad8_signal_read(struct counter_device *counter,
 			     struct counter_signal *signal,
 			     enum counter_signal_level *level)
@@ -156,18 +155,10 @@ static int quad8_count_read(struct counter_device *counter,
 {
 	struct quad8 *const priv = counter_priv(counter);
 	struct channel_reg __iomem *const chan = priv->reg->channel + count->id;
-	unsigned int flags;
-	unsigned int borrow;
-	unsigned int carry;
 	unsigned long irqflags;
 	int i;
 
-	flags = ioread8(&chan->control);
-	borrow = flags & QUAD8_FLAG_BT;
-	carry = !!(flags & QUAD8_FLAG_CT);
-
-	/* Borrow XOR Carry effectively doubles count range */
-	*val = (unsigned long)(borrow ^ carry) << 24;
+	*val = 0;
 
 	spin_lock_irqsave(&priv->lock, irqflags);
 
@@ -191,8 +182,7 @@ static int quad8_count_write(struct counter_device *counter,
 	unsigned long irqflags;
 	int i;
 
-	/* Only 24-bit values are supported */
-	if (val > 0xFFFFFF)
+	if (val > LS7267_CNTR_MAX)
 		return -ERANGE;
 
 	spin_lock_irqsave(&priv->lock, irqflags);
@@ -806,8 +796,7 @@ static int quad8_count_preset_write(struct counter_device *counter,
 	struct quad8 *const priv = counter_priv(counter);
 	unsigned long irqflags;
 
-	/* Only 24-bit values are supported */
-	if (preset > 0xFFFFFF)
+	if (preset > LS7267_CNTR_MAX)
 		return -ERANGE;
 
 	spin_lock_irqsave(&priv->lock, irqflags);
@@ -834,8 +823,7 @@ static int quad8_count_ceiling_read(struct counter_device *counter,
 		*ceiling = priv->preset[count->id];
 		break;
 	default:
-		/* By default 0x1FFFFFF (25 bits unsigned) is maximum count */
-		*ceiling = 0x1FFFFFF;
+		*ceiling = LS7267_CNTR_MAX;
 		break;
 	}
 
@@ -850,8 +838,7 @@ static int quad8_count_ceiling_write(struct counter_device *counter,
 	struct quad8 *const priv = counter_priv(counter);
 	unsigned long irqflags;
 
-	/* Only 24-bit values are supported */
-	if (ceiling > 0xFFFFFF)
+	if (ceiling > LS7267_CNTR_MAX)
 		return -ERANGE;
 
 	spin_lock_irqsave(&priv->lock, irqflags);

base-commit: fe15c26ee26efa11741a7b632e9f23b01aca4cc6
-- 
2.39.2

[PATCH 5.15 v3 2/6] counter: 104-quad-8: Fix race condition between FLAG and CNTR reads

[William Breathitt Gray]

The Counter (CNTR) register is 24 bits wide, but we can have an
effective 25-bit count value by setting bit 24 to the XOR of the Borrow
flag and Carry flag. The flags can be read from the FLAG register, but a
race condition exists: the Borrow flag and Carry flag are instantaneous
and could change by the time the count value is read from the CNTR
register.

Since the race condition could result in an incorrect 25-bit count
value, remove support for 25-bit count values from this driver.

Fixes: 28e5d3bb0325 ("iio: 104-quad-8: Add IIO support for the ACCES 104-QUAD-8")
Cc: <stable@vger.kernel.org> # 5.15.x
Signed-off-by: William Breathitt Gray <william.gray@linaro.org>
---
 drivers/counter/104-quad-8.c | 18 +++---------------
 1 file changed, 3 insertions(+), 15 deletions(-)

diff --git a/drivers/counter/104-quad-8.c b/drivers/counter/104-quad-8.c
index 0caa60537..643aae0c9 100644
--- a/drivers/counter/104-quad-8.c
+++ b/drivers/counter/104-quad-8.c
@@ -61,10 +61,6 @@ struct quad8 {
 #define QUAD8_REG_CHAN_OP 0x11
 #define QUAD8_REG_INDEX_INPUT_LEVELS 0x16
 #define QUAD8_DIFF_ENCODER_CABLE_STATUS 0x17
-/* Borrow Toggle flip-flop */
-#define QUAD8_FLAG_BT BIT(0)
-/* Carry Toggle flip-flop */
-#define QUAD8_FLAG_CT BIT(1)
 /* Error flag */
 #define QUAD8_FLAG_E BIT(4)
 /* Up/Down flag */
@@ -121,17 +117,9 @@ static int quad8_count_read(struct counter_device *counter,
 {
 	struct quad8 *const priv = counter->priv;
 	const int base_offset = priv->base + 2 * count->id;
-	unsigned int flags;
-	unsigned int borrow;
-	unsigned int carry;
 	int i;
 
-	flags = inb(base_offset + 1);
-	borrow = flags & QUAD8_FLAG_BT;
-	carry = !!(flags & QUAD8_FLAG_CT);
-
-	/* Borrow XOR Carry effectively doubles count range */
-	*val = (unsigned long)(borrow ^ carry) << 24;
+	*val = 0;
 
 	mutex_lock(&priv->lock);
 
@@ -699,8 +687,8 @@ static ssize_t quad8_count_ceiling_read(struct counter_device *counter,
 
 	mutex_unlock(&priv->lock);
 
-	/* By default 0x1FFFFFF (25 bits unsigned) is maximum count */
-	return sprintf(buf, "33554431\n");
+	/* By default 0xFFFFFF (24 bits unsigned) is maximum count */
+	return sprintf(buf, "16777215\n");
 }
 
 static ssize_t quad8_count_ceiling_write(struct counter_device *counter,

base-commit: bbf9f29bac04f85bbf45af172dcdc9664d8808cb
-- 
2.39.2

[PATCH 5.10 v3 3/6] counter: 104-quad-8: Fix race condition between FLAG and CNTR reads

[William Breathitt Gray]

The Counter (CNTR) register is 24 bits wide, but we can have an
effective 25-bit count value by setting bit 24 to the XOR of the Borrow
flag and Carry flag. The flags can be read from the FLAG register, but a
race condition exists: the Borrow flag and Carry flag are instantaneous
and could change by the time the count value is read from the CNTR
register.

Since the race condition could result in an incorrect 25-bit count
value, remove support for 25-bit count values from this driver.

Fixes: 28e5d3bb0325 ("iio: 104-quad-8: Add IIO support for the ACCES 104-QUAD-8")
Cc: <stable@vger.kernel.org> # 5.10.x
Signed-off-by: William Breathitt Gray <william.gray@linaro.org>
---
 drivers/counter/104-quad-8.c | 18 +++---------------
 1 file changed, 3 insertions(+), 15 deletions(-)

diff --git a/drivers/counter/104-quad-8.c b/drivers/counter/104-quad-8.c
index 21bb2bb76..1b4fdee9d 100644
--- a/drivers/counter/104-quad-8.c
+++ b/drivers/counter/104-quad-8.c
@@ -62,10 +62,6 @@ struct quad8_iio {
 #define QUAD8_REG_CHAN_OP 0x11
 #define QUAD8_REG_INDEX_INPUT_LEVELS 0x16
 #define QUAD8_DIFF_ENCODER_CABLE_STATUS 0x17
-/* Borrow Toggle flip-flop */
-#define QUAD8_FLAG_BT BIT(0)
-/* Carry Toggle flip-flop */
-#define QUAD8_FLAG_CT BIT(1)
 /* Error flag */
 #define QUAD8_FLAG_E BIT(4)
 /* Up/Down flag */
@@ -643,17 +639,9 @@ static int quad8_count_read(struct counter_device *counter,
 {
 	struct quad8_iio *const priv = counter->priv;
 	const int base_offset = priv->base + 2 * count->id;
-	unsigned int flags;
-	unsigned int borrow;
-	unsigned int carry;
 	int i;
 
-	flags = inb(base_offset + 1);
-	borrow = flags & QUAD8_FLAG_BT;
-	carry = !!(flags & QUAD8_FLAG_CT);
-
-	/* Borrow XOR Carry effectively doubles count range */
-	*val = (unsigned long)(borrow ^ carry) << 24;
+	*val = 0;
 
 	mutex_lock(&priv->lock);
 
@@ -1198,8 +1186,8 @@ static ssize_t quad8_count_ceiling_read(struct counter_device *counter,
 
 	mutex_unlock(&priv->lock);
 
-	/* By default 0x1FFFFFF (25 bits unsigned) is maximum count */
-	return sprintf(buf, "33554431\n");
+	/* By default 0xFFFFFF (24 bits unsigned) is maximum count */
+	return sprintf(buf, "16777215\n");
 }
 
 static ssize_t quad8_count_ceiling_write(struct counter_device *counter,

base-commit: e5f315b55f8e09ac17c968da42f9345f64efcdd2
-- 
2.39.2

[PATCH 5.4 v3 4/6] counter: 104-quad-8: Fix race condition between FLAG and CNTR reads

[William Breathitt Gray]

The Counter (CNTR) register is 24 bits wide, but we can have an
effective 25-bit count value by setting bit 24 to the XOR of the Borrow
flag and Carry flag. The flags can be read from the FLAG register, but a
race condition exists: the Borrow flag and Carry flag are instantaneous
and could change by the time the count value is read from the CNTR
register.

Since the race condition could result in an incorrect 25-bit count
value, remove support for 25-bit count values from this driver.

Fixes: 28e5d3bb0325 ("iio: 104-quad-8: Add IIO support for the ACCES 104-QUAD-8")
Cc: <stable@vger.kernel.org> # 5.4.x
Signed-off-by: William Breathitt Gray <william.gray@linaro.org>
---
 drivers/counter/104-quad-8.c | 20 +++-----------------
 1 file changed, 3 insertions(+), 17 deletions(-)

diff --git a/drivers/counter/104-quad-8.c b/drivers/counter/104-quad-8.c
index f261a57af..48de69f58 100644
--- a/drivers/counter/104-quad-8.c
+++ b/drivers/counter/104-quad-8.c
@@ -57,10 +57,6 @@ struct quad8_iio {
 
 #define QUAD8_REG_CHAN_OP 0x11
 #define QUAD8_REG_INDEX_INPUT_LEVELS 0x16
-/* Borrow Toggle flip-flop */
-#define QUAD8_FLAG_BT BIT(0)
-/* Carry Toggle flip-flop */
-#define QUAD8_FLAG_CT BIT(1)
 /* Error flag */
 #define QUAD8_FLAG_E BIT(4)
 /* Up/Down flag */
@@ -639,19 +635,9 @@ static int quad8_count_read(struct counter_device *counter,
 {
 	struct quad8_iio *const priv = counter->priv;
 	const int base_offset = priv->base + 2 * count->id;
-	unsigned int flags;
-	unsigned int borrow;
-	unsigned int carry;
-	unsigned long position;
+	unsigned long position = 0;
 	int i;
 
-	flags = inb(base_offset + 1);
-	borrow = flags & QUAD8_FLAG_BT;
-	carry = !!(flags & QUAD8_FLAG_CT);
-
-	/* Borrow XOR Carry effectively doubles count range */
-	position = (unsigned long)(borrow ^ carry) << 24;
-
 	mutex_lock(&priv->lock);
 
 	/* Reset Byte Pointer; transfer Counter to Output Latch */
@@ -1204,8 +1190,8 @@ static ssize_t quad8_count_ceiling_read(struct counter_device *counter,
 
 	mutex_unlock(&priv->lock);
 
-	/* By default 0x1FFFFFF (25 bits unsigned) is maximum count */
-	return sprintf(buf, "33554431\n");
+	/* By default 0xFFFFFF (24 bits unsigned) is maximum count */
+	return sprintf(buf, "16777215\n");
 }
 
 static ssize_t quad8_count_ceiling_write(struct counter_device *counter,

base-commit: 126ee8982bfcae6111f0fd157ee5cdd0ec7f5ca5
-- 
2.39.2

[PATCH 4.19 v3 5/6] iio: counter: 104-quad-8: Fix race condition between FLAG and CNTR reads

[William Breathitt Gray]

The Counter (CNTR) register is 24 bits wide, but we can have an
effective 25-bit count value by setting bit 24 to the XOR of the Borrow
flag and Carry flag. The flags can be read from the FLAG register, but a
race condition exists: the Borrow flag and Carry flag are instantaneous
and could change by the time the count value is read from the CNTR
register.

Since the race condition could result in an incorrect 25-bit count
value, remove support for 25-bit count values from this driver.

Fixes: 28e5d3bb0325 ("iio: 104-quad-8: Add IIO support for the ACCES 104-QUAD-8")
Cc: <stable@vger.kernel.org> # 4.19.x
Signed-off-by: William Breathitt Gray <william.gray@linaro.org>
---
 drivers/iio/counter/104-quad-8.c | 14 +-------------
 1 file changed, 1 insertion(+), 13 deletions(-)

diff --git a/drivers/iio/counter/104-quad-8.c b/drivers/iio/counter/104-quad-8.c
index 92be8d0f7..92e68cada 100644
--- a/drivers/iio/counter/104-quad-8.c
+++ b/drivers/iio/counter/104-quad-8.c
@@ -61,10 +61,6 @@ struct quad8_iio {
 
 #define QUAD8_REG_CHAN_OP 0x11
 #define QUAD8_REG_INDEX_INPUT_LEVELS 0x16
-/* Borrow Toggle flip-flop */
-#define QUAD8_FLAG_BT BIT(0)
-/* Carry Toggle flip-flop */
-#define QUAD8_FLAG_CT BIT(1)
 /* Error flag */
 #define QUAD8_FLAG_E BIT(4)
 /* Up/Down flag */
@@ -97,9 +93,6 @@ static int quad8_read_raw(struct iio_dev *indio_dev,
 {
 	struct quad8_iio *const priv = iio_priv(indio_dev);
 	const int base_offset = priv->base + 2 * chan->channel;
-	unsigned int flags;
-	unsigned int borrow;
-	unsigned int carry;
 	int i;
 
 	switch (mask) {
@@ -110,12 +103,7 @@ static int quad8_read_raw(struct iio_dev *indio_dev,
 			return IIO_VAL_INT;
 		}
 
-		flags = inb(base_offset + 1);
-		borrow = flags & QUAD8_FLAG_BT;
-		carry = !!(flags & QUAD8_FLAG_CT);
-
-		/* Borrow XOR Carry effectively doubles count range */
-		*val = (borrow ^ carry) << 24;
+		*val = 0;
 
 		/* Reset Byte Pointer; transfer Counter to Output Latch */
 		outb(QUAD8_CTR_RLD | QUAD8_RLD_RESET_BP | QUAD8_RLD_CNTR_OUT,

base-commit: 6a98afd74b4c2016fb87f5c3b7ce1c53ac215c13
-- 
2.39.2

[PATCH 4.14 v3 6/6] iio: counter: 104-quad-8: Fix race condition between FLAG and CNTR reads

[William Breathitt Gray]

The Counter (CNTR) register is 24 bits wide, but we can have an
effective 25-bit count value by setting bit 24 to the XOR of the Borrow
flag and Carry flag. The flags can be read from the FLAG register, but a
race condition exists: the Borrow flag and Carry flag are instantaneous
and could change by the time the count value is read from the CNTR
register.

Since the race condition could result in an incorrect 25-bit count
value, remove support for 25-bit count values from this driver.

Fixes: 28e5d3bb0325 ("iio: 104-quad-8: Add IIO support for the ACCES 104-QUAD-8")
Cc: <stable@vger.kernel.org> # 4.14.x
Signed-off-by: William Breathitt Gray <william.gray@linaro.org>
---
 drivers/iio/counter/104-quad-8.c | 10 +---------
 1 file changed, 1 insertion(+), 9 deletions(-)

diff --git a/drivers/iio/counter/104-quad-8.c b/drivers/iio/counter/104-quad-8.c
index 181585ae..bdb07694 100644
--- a/drivers/iio/counter/104-quad-8.c
+++ b/drivers/iio/counter/104-quad-8.c
@@ -64,9 +64,6 @@ static int quad8_read_raw(struct iio_dev *indio_dev,
 {
 	struct quad8_iio *const priv = iio_priv(indio_dev);
 	const int base_offset = priv->base + 2 * chan->channel;
-	unsigned int flags;
-	unsigned int borrow;
-	unsigned int carry;
 	int i;
 
 	switch (mask) {
@@ -76,12 +73,7 @@ static int quad8_read_raw(struct iio_dev *indio_dev,
 			return IIO_VAL_INT;
 		}
 
-		flags = inb(base_offset + 1);
-		borrow = flags & BIT(0);
-		carry = !!(flags & BIT(1));
-
-		/* Borrow XOR Carry effectively doubles count range */
-		*val = (borrow ^ carry) << 24;
+		*val = 0;
 
 		/* Reset Byte Pointer; transfer Counter to Output Latch */
 		outb(0x11, base_offset + 1);

base-commit: 373c2a0d721acdbed9f45bf9816c04edad3704ca
-- 
2.39.2

Re: [PATCH 6.1,6.2,6.3 v3 1/6] counter: 104-quad-8: Fix race condition between FLAG and CNTR reads

[William Breathitt Gray]

[-- Attachment #1: Type: text/plain, Size: 989 bytes --]

On Sun, Mar 12, 2023 at 07:15:49PM -0400, William Breathitt Gray wrote:
> The Counter (CNTR) register is 24 bits wide, but we can have an
> effective 25-bit count value by setting bit 24 to the XOR of the Borrow
> flag and Carry flag. The flags can be read from the FLAG register, but a
> race condition exists: the Borrow flag and Carry flag are instantaneous
> and could change by the time the count value is read from the CNTR
> register.
> 
> Since the race condition could result in an incorrect 25-bit count
> value, remove support for 25-bit count values from this driver;
> hard-coded maximum count values are replaced by a LS7267_CNTR_MAX define
> for consistency and clarity.
> 
> Fixes: 28e5d3bb0325 ("iio: 104-quad-8: Add IIO support for the ACCES 104-QUAD-8")
> Cc: <stable@vger.kernel.org> # 6.1.x
> Cc: <stable@vger.kernel.org> # 6.2.x
> Signed-off-by: William Breathitt Gray <william.gray@linaro.org>

Applied to counter-fixes.

William Breathitt Gray

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 228 bytes --]