am7xxx: add comment about detaching kernel drivers before setting configuration

[libam7xxx.git] / src / am7xxx.c

diff --git a/src/am7xxx.c b/src/am7xxx.c
index 3334615..6595ccf 100644 (file)
--- a/src/am7xxx.c
+++ b/src/am7xxx.c
@@ -34,7 +34,7 @@
  * taken from: http://unixwiz.net/techtips/gnu-c-attributes.html)
  */
 #ifndef __GNUC__
-#  define  __attribute__(x)  /*NOTHING*/
+#  define  __attribute__(x)  /* NOTHING */
 #endif
 
 /* Control shared library symbols visibility */
@@ -385,8 +385,8 @@ static int read_data(am7xxx_device *dev, uint8_t *buffer, unsigned int len)
 
        ret = libusb_bulk_transfer(dev->usb_device, 0x81, buffer, len, &transferred, 0);
        if (ret != 0 || (unsigned int)transferred != len) {
-               error(dev->ctx, "ret: %d\ttransferred: %d (expected %u)\n",
-                     ret, transferred, len);
+               error(dev->ctx, "%s. Transferred: %d (expected %u)\n",
+                     libusb_error_name(ret), transferred, len);
                return ret;
        }
 
@@ -404,8 +404,8 @@ static int send_data(am7xxx_device *dev, uint8_t *buffer, unsigned int len)
 
        ret = libusb_bulk_transfer(dev->usb_device, 0x1, buffer, len, &transferred, 0);
        if (ret != 0 || (unsigned int)transferred != len) {
-               error(dev->ctx, "ret: %d\ttransferred: %d (expected %u)\n",
-                     ret, transferred, len);
+               error(dev->ctx, "%s. Transferred: %d (expected %u)\n",
+                     libusb_error_name(ret), transferred, len);
                return ret;
        }
 
@@ -704,10 +704,11 @@ static am7xxx_device *find_device(am7xxx_context *ctx,
 
 static int open_device(am7xxx_context *ctx,
                       unsigned int device_index,
-                      libusb_device* usb_dev,
+                      libusb_device *usb_dev,
                       am7xxx_device **dev)
 {
        int ret;
+       int current_configuration;
 
        *dev = find_device(ctx, device_index);
        if (*dev == NULL) {
@@ -724,7 +725,7 @@ static int open_device(am7xxx_context *ctx,
 
        ret = libusb_open(usb_dev, &((*dev)->usb_device));
        if (ret < 0) {
-               debug(ctx, "libusb_open failed\n");
+               debug(ctx, "libusb_open failed: %s\n", libusb_error_name(ret));
                goto out;
        }
 
@@ -732,27 +733,59 @@ static int open_device(am7xxx_context *ctx,
         * to close it again before bailing out.
         */
 
-       ret = libusb_set_configuration((*dev)->usb_device,
-                                      (*dev)->desc->configuration);
-       if (ret < 0) {
-               debug(ctx, "libusb_set_configuration failed\n");
-               debug(ctx, "Cannot set configuration %hhu\n",
-                     (*dev)->desc->configuration);
-               goto out_libusb_close;
+       current_configuration = -1;
+       libusb_get_configuration((*dev)->usb_device, &current_configuration);
+       if (current_configuration != (*dev)->desc->configuration) {
+               /*
+                * In principle kernel drivers bound to each interface should
+                * be detached before setting the configuration, but in
+                * practice this is not necessary for most devices.
+                *
+                * For example something like the following function would be
+                * called:
+                *      libusb_detach_all_kernel_drivers((*dev)->usb_device);
+                */
+               ret = libusb_set_configuration((*dev)->usb_device,
+                                              (*dev)->desc->configuration);
+               if (ret < 0) {
+                       debug(ctx, "libusb_set_configuration failed: %s\n",
+                             libusb_error_name(ret));
+                       debug(ctx, "Cannot set configuration %hhu\n",
+                             (*dev)->desc->configuration);
+                       goto out_libusb_close;
+               }
        }
 
+       libusb_set_auto_detach_kernel_driver((*dev)->usb_device, 1);
+
        ret = libusb_claim_interface((*dev)->usb_device,
                                     (*dev)->desc->interface_number);
        if (ret < 0) {
-               debug(ctx, "libusb_claim_interface failed\n");
+               debug(ctx, "libusb_claim_interface failed: %s\n",
+                     libusb_error_name(ret));
                debug(ctx, "Cannot claim interface %hhu\n",
                      (*dev)->desc->interface_number);
-out_libusb_close:
-               libusb_close((*dev)->usb_device);
-               (*dev)->usb_device = NULL;
+               goto out_libusb_close;
+       }
+
+       /* Checking that the configuration has not changed, as suggested in
+        * http://libusb.sourceforge.net/api-1.0/caveats.html
+        */
+       current_configuration = -1;
+       libusb_get_configuration((*dev)->usb_device, &current_configuration);
+       if (current_configuration != (*dev)->desc->configuration) {
+               debug(ctx, "libusb configuration changed\n");
+               debug(ctx, "Cannot claim interface %hhu\n",
+                     (*dev)->desc->interface_number);
+               goto out_libusb_close;
        }
 out:
        return ret;
+
+out_libusb_close:
+       libusb_close((*dev)->usb_device);
+       (*dev)->usb_device = NULL;
+       return ret;
 }
 
 typedef enum {
@@ -764,13 +797,14 @@ typedef enum {
  * This is where the central logic of multi-device support is.
  *
  * When 'op' == SCAN_OP_BUILD_DEVLIST the parameters 'open_device_index' and
- * 'dev' are ignored; the function returns 0 on success and a negative value
+ * 'dev' are ignored; the function returns 0 on success or a negative value
  * on error.
  *
  * When 'op' == SCAN_OP_OPEN_DEVICE the function opens the supported USB
  * device with index 'open_device_index' and returns the correspondent
- * am7xxx_device in the 'dev' parameter; the function returns 0 on success,
- * 1 if the device was already open and a negative value on error.
+ * am7xxx_device in the 'dev' parameter; the function returns the value from
+ * open_device(), which is 0 on success, 1 if the device was already open or
+ * a negative value on error.
  *
  * NOTES:
  * if scan_devices() fails when called with 'op' == SCAN_OP_BUILD_DEVLIST,
@@ -781,7 +815,7 @@ static int scan_devices(am7xxx_context *ctx, scan_op op,
                        unsigned int open_device_index, am7xxx_device **dev)
 {
        ssize_t num_devices;
-       libusb_device** list;
+       libusb_device **list;
        unsigned int current_index;
        int i;
        int ret;