[PATCH v6 2/5] Add support for USBTMC USB488 SRQ notification with fasync

[Dave Penkler]

Background:
By configuring an instrument's event status register various
conditions can be reported via an SRQ notification. This complements
the synchronous polling approach using the READ_STATUS_BYTE ioctl
with an asynchronous notification.

Signed-off-by: Dave Penkler <dpenk...@gmail.com>
---
 drivers/usb/class/usbtmc.c | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/drivers/usb/class/usbtmc.c b/drivers/usb/class/usbtmc.c
index 89456df9..7bfd6ec 100644
--- a/drivers/usb/class/usbtmc.c
+++ b/drivers/usb/class/usbtmc.c
@@ -99,6 +99,7 @@ struct usbtmc_device_data {
        int            iin_interval;
        struct urb    *iin_urb;
        u16            iin_wMaxPacketSize;
+       atomic_t       srq_asserted;
 
        u8 rigol_quirk;
 
@@ -113,6 +114,7 @@ struct usbtmc_device_data {
        struct kref kref;
        struct mutex io_mutex;  /* only one i/o function running at a time */
        wait_queue_head_t waitq;
+       struct fasync_struct *fasync;
 };
 #define to_usbtmc_data(d) container_of(d, struct usbtmc_device_data, kref)
 
@@ -404,6 +406,9 @@ static int usbtmc488_ioctl_read_stb(struct 
usbtmc_device_data *data,
 
        atomic_set(&data->iin_data_valid, 0);
 
+       /* must issue read_stb before using poll or select */
+       atomic_set(&data->srq_asserted, 0);
+
        rv = usb_control_msg(data->usb_dev,
                        usb_rcvctrlpipe(data->usb_dev, 0),
                        USBTMC488_REQUEST_READ_STATUS_BYTE,
@@ -1171,6 +1176,13 @@ skip_io_on_zombie:
        return retval;
 }
 
+static int usbtmc_fasync(int fd, struct file *file, int on)
+{
+       struct usbtmc_device_data *data = file->private_data;
+
+       return fasync_helper(fd, file, on, &data->fasync);
+}
+
 static const struct file_operations fops = {
        .owner          = THIS_MODULE,
        .read           = usbtmc_read,
@@ -1178,6 +1190,7 @@ static const struct file_operations fops = {
        .open           = usbtmc_open,
        .release        = usbtmc_release,
        .unlocked_ioctl = usbtmc_ioctl,
+       .fasync         = usbtmc_fasync,
        .llseek         = default_llseek,
 };
 
@@ -1207,6 +1220,16 @@ static void usbtmc_interrupt(struct urb *urb)
                        wake_up_interruptible(&data->waitq);
                        goto exit;
                }
+               /* check for SRQ notification */
+               if (data->iin_buffer[0] == 0x81) {
+                       if (data->fasync)
+                               kill_fasync(&data->fasync,
+                                       SIGIO, POLL_IN);
+
+                       atomic_set(&data->srq_asserted, 1);
+                       wake_up_interruptible(&data->waitq);
+                       goto exit;
+               }
                dev_warn(dev, "invalid notification: %x\n", 
data->iin_buffer[0]);
                break;
        case -EOVERFLOW:
@@ -1262,6 +1285,7 @@ static int usbtmc_probe(struct usb_interface *intf,
        mutex_init(&data->io_mutex);
        init_waitqueue_head(&data->waitq);
        atomic_set(&data->iin_data_valid, 0);
+       atomic_set(&data->srq_asserted, 0);
        data->zombie = 0;
 
        /* Determine if it is a Rigol or not */
-- 
2.6.3
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