Re: [PATCH 09/12] usb: usbtmc: Fix ioctl USBTMC_IOCTL_CLEAR

[Oliver Neukum]

Am Donnerstag, den 17.05.2018, 19:03 +0200 schrieb Guido Kiener:
> Insert a sleep of 50 ms between subsequent CHECK_CLEAR_STATUS
> control requests to avoid stressing the instrument with repeated
> requests.
> 
> Some instruments need time to cleanup internal I/O buffers.
> Polling and repeated requests slow down the response time of
> devices.

The connection between the patch and the description is loose.

Regards
Oliver

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[PATCH 09/12] usb: usbtmc: Fix ioctl USBTMC_IOCTL_CLEAR

[Guido Kiener]

Insert a sleep of 50 ms between subsequent CHECK_CLEAR_STATUS
control requests to avoid stressing the instrument with repeated
requests.

Some instruments need time to cleanup internal I/O buffers.
Polling and repeated requests slow down the response time of
devices.

Signed-off-by: Guido Kiener 
Reviewed-by: Steve Bayless 
---
 drivers/usb/class/usbtmc.c | 46 +++---
 1 file changed, 18 insertions(+), 28 deletions(-)

diff --git a/drivers/usb/class/usbtmc.c b/drivers/usb/class/usbtmc.c
index 76b0a7b083a7..165b707991f3 100644
--- a/drivers/usb/class/usbtmc.c
+++ b/drivers/usb/class/usbtmc.c
@@ -1643,20 +1643,17 @@ static ssize_t usbtmc_write(struct file *filp, const 
char __user *buf,
 
 static int usbtmc_ioctl_clear(struct usbtmc_device_data *data)
 {
-   struct usb_host_interface *current_setting;
-   struct usb_endpoint_descriptor *desc;
struct device *dev;
u8 *buffer;
int rv;
int n;
int actual = 0;
-   int max_size;
 
dev = >intf->dev;
 
dev_dbg(dev, "Sending INITIATE_CLEAR request\n");
 
-   buffer = kmalloc(USBTMC_SIZE_IOBUFFER, GFP_KERNEL);
+   buffer = kmalloc(USBTMC_BUFSIZE, GFP_KERNEL);
if (!buffer)
return -ENOMEM;
 
@@ -1664,7 +1661,7 @@ static int usbtmc_ioctl_clear(struct usbtmc_device_data 
*data)
 usb_rcvctrlpipe(data->usb_dev, 0),
 USBTMC_REQUEST_INITIATE_CLEAR,
 USB_DIR_IN | USB_TYPE_CLASS | USB_RECIP_INTERFACE,
-0, 0, buffer, 1, USBTMC_TIMEOUT);
+0, 0, buffer, 1, USB_CTRL_GET_TIMEOUT);
if (rv < 0) {
dev_err(dev, "usb_control_msg returned %d\n", rv);
goto exit;
@@ -1678,22 +1675,6 @@ static int usbtmc_ioctl_clear(struct usbtmc_device_data 
*data)
goto exit;
}
 
-   max_size = 0;
-   current_setting = data->intf->cur_altsetting;
-   for (n = 0; n < current_setting->desc.bNumEndpoints; n++) {
-   desc = _setting->endpoint[n].desc;
-   if (desc->bEndpointAddress == data->bulk_in)
-   max_size = usb_endpoint_maxp(desc);
-   }
-
-   if (max_size == 0) {
-   dev_err(dev, "Couldn't get wMaxPacketSize\n");
-   rv = -EPERM;
-   goto exit;
-   }
-
-   dev_dbg(dev, "wMaxPacketSize is %d\n", max_size);
-
n = 0;
 
 usbtmc_clear_check_status:
@@ -1704,7 +1685,7 @@ static int usbtmc_ioctl_clear(struct usbtmc_device_data 
*data)
 usb_rcvctrlpipe(data->usb_dev, 0),
 USBTMC_REQUEST_CHECK_CLEAR_STATUS,
 USB_DIR_IN | USB_TYPE_CLASS | USB_RECIP_INTERFACE,
-0, 0, buffer, 2, USBTMC_TIMEOUT);
+0, 0, buffer, 2, USB_CTRL_GET_TIMEOUT);
if (rv < 0) {
dev_err(dev, "usb_control_msg returned %d\n", rv);
goto exit;
@@ -1721,15 +1702,19 @@ static int usbtmc_ioctl_clear(struct usbtmc_device_data 
*data)
goto exit;
}
 
-   if (buffer[1] == 1)
+   if ((buffer[1] & 1) != 0) {
do {
dev_dbg(dev, "Reading from bulk in EP\n");
 
rv = usb_bulk_msg(data->usb_dev,
  usb_rcvbulkpipe(data->usb_dev,
  data->bulk_in),
- buffer, USBTMC_SIZE_IOBUFFER,
- , USBTMC_TIMEOUT);
+ buffer, USBTMC_BUFSIZE,
+ , USB_CTRL_GET_TIMEOUT);
+
+   print_hex_dump_debug("usbtmc ", DUMP_PREFIX_NONE,
+16, 1, buffer, actual, true);
+
n++;
 
if (rv < 0) {
@@ -1737,10 +1722,15 @@ static int usbtmc_ioctl_clear(struct usbtmc_device_data 
*data)
rv);
goto exit;
}
-   } while ((actual == max_size) &&
+   } while ((actual == USBTMC_BUFSIZE) &&
  (n < USBTMC_MAX_READS_TO_CLEAR_BULK_IN));
+   } else {
+   /* do not stress device with subsequent requests */
+   msleep(50);
+   n++;
+   }
 
-   if (actual == max_size) {
+   if (n >= USBTMC_MAX_READS_TO_CLEAR_BULK_IN) {
dev_err(dev, "Couldn't clear device buffer within %d cycles\n",
USBTMC_MAX_READS_TO_CLEAR_BULK_IN);
rv = -EPERM;
@@ -1754,7 +1744,7 @@ static int usbtmc_ioctl_clear(struct usbtmc_device_data 
*data)
rv =