USB: usbtmc: Fix stale status byte ioctl

PATCH In review Dave Penkler 2 participants 6 messages Dec 15, 2020 – Dec 28, 2020 USB

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Dave Penkler

author

2020-12-15 15:58 UTC #0 lore raw

cover USB: usbtmc: Fix stale status byte ioctl

The ioctl USBTMC488_IOCTL_READ_STB either returns a cached status byte (STB) sent by the device due to a service request (SRQ) condition or the STB obtained from a query to the device with a READ_STATUS_BYTE control message.

When the query is interrupted by an SRQ message on the interrupt pipe, the ioctl still returns the requested STB while the STB of the out-of-band SRQ message is cached for the next call of this ioctl. However the cached SRQ STB represents a state that was previous to the last returned STB. Furthermore the cached SRQ STB can be stale and not reflect the current state of the device.

This set of patches separates out the behaviour into 3 ioctls:

[PATCH 1]
USBTMC488_IOCTL_READ_STB always reads the STB from the device and if the associated file descriptor has the srq_asserted bit set it ors in the RQS bit to the returned STB and clears the srq_asserted bit conformant to subclass USB488 devices.

[PATCH 2]
USBTMC_IOCTL_GET_STB reads the status byte (STB) from the device and returns the STB unmodified to the application. The srq_asserted bit is not taken into account and not changed.

[PATCH 3]
USBTMC_IOCTL_GET_SRQ_STB only returns the status byte (STB) that was originally sent by the device due to a service request (SRQ) condition.

This ioctl checks the srq_asserted bit of the associated file descriptor. If set, the srq_asserted bit is reset and the cached STB with original SRQ information is returned. Otherwise the ioctl returns the error code ENOMSG.

The latter 2 ioctls are useful to support non USBTMC-488 compliant devices. Time sensitive applications can read the cached STB without incurring the cost of an urb transaction over the bus.

[PATCH 4]
Increase the API version number

Dave Penkler (4):
USB: usbtmc: Fix reading stale status byte
USB: usbtmc: Add USBTMC_IOCTL_GET_STB
USB: usbtmc: Add separate USBTMC_IOCTL_GET_SRQ_STB
USB: usbtmc: Bump USBTMC_API_VERSION value

 drivers/usb/class/usbtmc.c   | 85 ++++++++++++++++++++++++++----------
 include/uapi/linux/usb/tmc.h |  3 ++
 2 files changed, 66 insertions(+), 22 deletions(-)

Signature · 1 line

2.29.2

Dave Penkler

author

2020-12-15 16:02 UTC #1 lore raw

PATCH 1/4 USB: usbtmc: Fix reading stale status byte

The fixed ioctl now always reads the STB from the device and if the associated file descriptor has the srq_asserted bit set it ors in the RQS bit to the returned STB and clears the srq_asserted bit conformant to subclass USB488 devices.

Signed-off-by Dave Penkler <[email protected]>

Reviewed-by Guido Kiener <[email protected]>

Tested-by Jian-Wei Wu <[email protected]>

---
 drivers/usb/class/usbtmc.c | 46 +++++++++++++++++++++-----------------
 1 file changed, 25 insertions(+), 21 deletions(-)

drivers/usb/class/usbtmc.c +25 ~~-21~~

index b222b777e6a4..189f06dcb7d3 100644
@@ -475,33 +475,17 @@ static int usbtmc_ioctl_abort_bulk_out(struct usbtmc_device_data *data)
 	return usbtmc_ioctl_abort_bulk_out_tag(data, data->bTag_last_write);
 }
 
-static int usbtmc488_ioctl_read_stb(struct usbtmc_file_data *file_data,
-				void __user *arg)
+static int usbtmc_get_stb(struct usbtmc_file_data *file_data, __u8 *stb)
 {
 	struct usbtmc_device_data *data = file_data->data;
 	struct device *dev = &data->intf->dev;
-	int srq_asserted = 0;
 	u8 *buffer;
 	u8 tag;
-	__u8 stb;
 	int rv;
 
 	dev_dbg(dev, "Enter ioctl_read_stb iin_ep_present: %d\n",
 		data->iin_ep_present);
 
-	spin_lock_irq(&data->dev_lock);
-	srq_asserted = atomic_xchg(&file_data->srq_asserted, srq_asserted);
-	if (srq_asserted) {
-		/* a STB with SRQ is already received */
-		stb = file_data->srq_byte;
-		spin_unlock_irq(&data->dev_lock);
-		rv = put_user(stb, (__u8 __user *)arg);
-		dev_dbg(dev, "stb:0x%02x with srq received %d\n",
-			(unsigned int)stb, rv);
-		return rv;
-	}
-	spin_unlock_irq(&data->dev_lock);
-
 	buffer = kmalloc(8, GFP_KERNEL);
 	if (!buffer)
 		return -ENOMEM;

@@ -548,13 +532,12 @@ static int usbtmc488_ioctl_read_stb(struct usbtmc_file_data *file_data,
 				data->iin_bTag, tag);
 		}
 
-		stb = data->bNotify2;
+		*stb = data->bNotify2;
 	} else {
-		stb = buffer[2];
+		*stb = buffer[2];
 	}
 
-	rv = put_user(stb, (__u8 __user *)arg);
-	dev_dbg(dev, "stb:0x%02x received %d\n", (unsigned int)stb, rv);
+	dev_dbg(dev, "stb:0x%02x received %d\n", (unsigned int)*stb, rv);
 
  exit:
 	/* bump interrupt bTag */

@@ -567,6 +550,27 @@ static int usbtmc488_ioctl_read_stb(struct usbtmc_file_data *file_data,
 	return rv;
 }
 
+static int usbtmc488_ioctl_read_stb(struct usbtmc_file_data *file_data,
+				void __user *arg)
+{
+	int srq_asserted = 0;
+	__u8 stb;
+	int rv;
+
+	rv = usbtmc_get_stb(file_data, &stb);
+
+	if (rv > 0) {
+		srq_asserted = atomic_xchg(&file_data->srq_asserted,
+					srq_asserted);
+		if (srq_asserted)
+			stb |= 0x40; /* Set RQS bit */
+
+		rv = put_user(stb, (__u8 __user *)arg);
+	}
+	return rv;
+
+}
+
 static int usbtmc488_ioctl_wait_srq(struct usbtmc_file_data *file_data,
 				    __u32 __user *arg)
 {

Signature · 1 line

2.29.2

Dave Penkler

author

2020-12-15 16:02 UTC #2 lore raw

PATCH 2/4 USB: usbtmc: Add USBTMC_IOCTL_GET_STB

In reply to Dave Penkler

This new ioctl reads the status byte (STB) from the device and returns the STB unmodified to the application. The srq_asserted bit is not taken into account and not changed.

This ioctl is useful to support non USBTMC-488 compliant devices.

Signed-off-by Dave Penkler <[email protected]>

Reviewed-by Guido Kiener <[email protected]>

Tested-by Jian-Wei Wu <[email protected]>

---
 drivers/usb/class/usbtmc.c   | 6 ++++++
 include/uapi/linux/usb/tmc.h | 2 ++
 2 files changed, 8 insertions(+)

drivers/usb/class/usbtmc.c +6 -0

index 189f06dcb7d3..8918e2182eca 100644
@@ -2149,6 +2149,12 @@ static long usbtmc_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 			file_data->auto_abort = !!tmp_byte;
 		break;
 
+	case USBTMC_IOCTL_GET_STB:
+		retval = usbtmc_get_stb(file_data, &tmp_byte);
+		if (retval > 0)
+			retval = put_user(tmp_byte, (__u8 __user *)arg);
+		break;
+
 	case USBTMC_IOCTL_CANCEL_IO:
 		retval = usbtmc_ioctl_cancel_io(file_data);
 		break;

include/uapi/linux/usb/tmc.h +2 -0

index fdd4d88a7b95..1e7878fe591f 100644
@@ -102,6 +102,8 @@ struct usbtmc_message {
 #define USBTMC_IOCTL_MSG_IN_ATTR	_IOR(USBTMC_IOC_NR, 24, __u8)
 #define USBTMC_IOCTL_AUTO_ABORT		_IOW(USBTMC_IOC_NR, 25, __u8)
 
+#define USBTMC_IOCTL_GET_STB            _IOR(USBTMC_IOC_NR, 26, __u8)
+
 /* Cancel and cleanup asynchronous calls */
 #define USBTMC_IOCTL_CANCEL_IO		_IO(USBTMC_IOC_NR, 35)
 #define USBTMC_IOCTL_CLEANUP_IO		_IO(USBTMC_IOC_NR, 36)

Signature · 1 line

2.29.2

Dave Penkler

author

2020-12-15 16:02 UTC #3 lore raw

PATCH 3/4 USB: usbtmc: Add separate USBTMC_IOCTL_GET_SRQ_STB

In reply to Dave Penkler

This new ioctl only returns the status byte (STB) that was originally sent by the device due to a service request (SRQ) condition.

This ioctl is useful to support non USBTMC-488 compliant devices. Time sensitive applications can read the cached STB without incurring the cost of an urb transaction over the bus.

Signed-off-by Dave Penkler <[email protected]>

Reviewed-by Guido Kiener <[email protected]>

Tested-by Jian-Wei Wu <[email protected]>

---
 drivers/usb/class/usbtmc.c   | 31 +++++++++++++++++++++++++++++++
 include/uapi/linux/usb/tmc.h |  1 +
 2 files changed, 32 insertions(+)

drivers/usb/class/usbtmc.c +31 -0

index 8918e2182eca..d2fcc698c745 100644
@@ -571,6 +571,32 @@ static int usbtmc488_ioctl_read_stb(struct usbtmc_file_data *file_data,
 
 }
 
+static int usbtmc_ioctl_get_srq_stb(struct usbtmc_file_data *file_data,
+				void __user *arg)
+{
+	struct usbtmc_device_data *data = file_data->data;
+	struct device *dev = &data->intf->dev;
+	int srq_asserted = 0;
+	__u8 stb = 0;
+	int rv;
+
+	spin_lock_irq(&data->dev_lock);
+	srq_asserted  = atomic_xchg(&file_data->srq_asserted, srq_asserted);
+
+	if (srq_asserted) {
+		stb = file_data->srq_byte;
+		spin_unlock_irq(&data->dev_lock);
+		rv = put_user(stb, (__u8 __user *)arg);
+	} else {
+		spin_unlock_irq(&data->dev_lock);
+		rv = -ENOMSG;
+	}
+
+	dev_dbg(dev, "stb:0x%02x with srq received %d\n", (unsigned int)stb, rv);
+
+	return rv;
+}
+
 static int usbtmc488_ioctl_wait_srq(struct usbtmc_file_data *file_data,
 				    __u32 __user *arg)
 {

@@ -2155,6 +2181,11 @@ static long usbtmc_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 			retval = put_user(tmp_byte, (__u8 __user *)arg);
 		break;
 
+	case USBTMC_IOCTL_GET_SRQ_STB:
+		retval = usbtmc_ioctl_get_srq_stb(file_data,
+						  (void __user *)arg);
+		break;
+
 	case USBTMC_IOCTL_CANCEL_IO:
 		retval = usbtmc_ioctl_cancel_io(file_data);
 		break;

include/uapi/linux/usb/tmc.h +1 -0

index 1e7878fe591f..d791cc58a7f0 100644
@@ -103,6 +103,7 @@ struct usbtmc_message {
 #define USBTMC_IOCTL_AUTO_ABORT		_IOW(USBTMC_IOC_NR, 25, __u8)
 
 #define USBTMC_IOCTL_GET_STB            _IOR(USBTMC_IOC_NR, 26, __u8)
+#define USBTMC_IOCTL_GET_SRQ_STB        _IOR(USBTMC_IOC_NR, 27, __u8)
 
 /* Cancel and cleanup asynchronous calls */
 #define USBTMC_IOCTL_CANCEL_IO		_IO(USBTMC_IOC_NR, 35)

Signature · 1 line

2.29.2

Dave Penkler

author

2020-12-15 16:00 UTC #4 lore raw

PATCH 4/4 USB: usbtmc: Bump USBTMC_API_VERSION value

In reply to Dave Penkler

The previous patches in this series have changed the behaviour of the driver and added new calls.

Signed-off-by Dave Penkler <[email protected]>

Reviewed-by Guido Kiener <[email protected]>

Tested-by Jian-Wei Wu <[email protected]>

---
 drivers/usb/class/usbtmc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

drivers/usb/class/usbtmc.c +1 -1

index d2fcc698c745..74d5a9c5238a 100644
@@ -25,7 +25,7 @@
 /* Increment API VERSION when changing tmc.h with new flags or ioctls
  * or when changing a significant behavior of the driver.
  */
-#define USBTMC_API_VERSION (2)
+#define USBTMC_API_VERSION (3)
 
 #define USBTMC_HEADER_SIZE	12
 #define USBTMC_MINOR_BASE	176

Signature · 1 line

2.29.2

Greg KH

maintainer

2020-12-28 14:49 UTC #5 lore raw

Re: [PATCH 4/4] USB: usbtmc: Bump USBTMC_API_VERSION value

Quoted 15 lines · Dave Penkler

The previous patches in this series have changed the behaviour of the driver and added new calls.
Signed-off-by Dave Penkler <[email protected]>
Reviewed-by Guido Kiener <[email protected]>
Tested-by Jian-Wei Wu <[email protected]>
---
 drivers/usb/class/usbtmc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
drivers/usb/class/usbtmc.c +0 -0
index d2fcc698c745..74d5a9c5238a 100644

drivers/usb/class/usbtmc.c line 28

Quoted 5 lines

drivers/usb/class/usbtmc.c +1 -1

@@ -25,7 +25,7 @@
 /* Increment API VERSION when changing tmc.h with new flags or ioctls
  * or when changing a significant behavior of the driver.
  */
-#define USBTMC_API_VERSION (2)
+#define USBTMC_API_VERSION (3)

Why is this needed? You should be able to detect new calls by just doing the ioctl and checking right?

I'll take this for now, but versioning apis is not a good thing to do in general.

thanks,

greg k-h