usb: gadget: uvc: Make bmControls attr read/write

For the Processing Unit and Camera Terminal descriptors defined in
the UVC Gadget we currently hard-code values into their bmControls
fields, which enumerates which controls the gadget is able to
support. This isn't appropriate since only the userspace companion
program to the kernel driver will know which controls are supported.
Make the configfs attributes that point to those fields read/write
so userspace can set them to appropriate values.

Document the new behaviour at the same time so the functionality is
clear.

Signed-off-by: Daniel Scally <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

Documentation/ABI/testing/configfs-usb-gadget-uvc

···
 KernelVersion:	4.0
 Description:	Default camera terminal descriptors
 
-		All attributes read only:
+		All attributes read only except bmControls, which is read/write:
 
 		========================  ====================================
 		bmControls		  bitmap specifying which controls are
···
 KernelVersion:	4.0
 Description:	Default processing unit descriptors
 
-		All attributes read only:
+		All attributes read only except bmControls, which is read/write:
 
 		===============	========================================
 		iProcessing	index of string descriptor

Documentation/usb/gadget_uvc.rst

···
 
 bNrInPins and baSourceID function in the same way.
 
+Configuring Supported Controls for Camera Terminal and Processing Unit
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The Camera Terminal and Processing Units in the UVC chain also have bmControls
+attributes which function similarly to the same field in an Extension Unit.
+Unlike XUs however, the meaning of the bitflag for these units is defined in
+the UVC specification; you should consult the "Camera Terminal Descriptor" and
+"Processing Unit Descriptor" sections for an enumeration of the flags.
+
+.. code-block:: bash
+
+        # Set the Processing Unit's bmControls, flagging Brightness, Contrast
+        # and Hue as available controls:
+        echo 0x05 > $FUNCTION/control/processing/default/bmControls
+
+        # Set the Camera Terminal's bmControls, flagging Focus Absolute and
+        # Focus Relative as available controls:
+        echo 0x60 > $FUNCTION/control/terminal/camera/default/bmControls
+
+If you do not set these fields then by default the Auto-Exposure Mode control
+for the Camera Terminal and the Brightness control for the Processing Unit will
+be flagged as available; if they are not supported you should set the field to
+0x00.
+
+Note that the size of the bmControls field for a Camera Terminal or Processing
+Unit is fixed by the UVC specification, and so the bControlSize attribute is
+read-only here.
+
 Custom Strings Support
 ~~~~~~~~~~~~~~~~~~~~~~
 

drivers/usb/gadget/function/uvc_configfs.c

···
 
 #undef UVCG_DEFAULT_PROCESSING_ATTR
 
+static ssize_t uvcg_default_processing_bm_controls_store(
+	struct config_item *item, const char *page, size_t len)
+{
+	struct config_group *group = to_config_group(item);
+	struct mutex *su_mutex = &group->cg_subsys->su_mutex;
+	struct uvc_processing_unit_descriptor *pd;
+	struct config_item *opts_item;
+	struct f_uvc_opts *opts;
+	u8 *bm_controls, *tmp;
+	unsigned int i;
+	int ret, n = 0;
+
+	mutex_lock(su_mutex);
+
+	opts_item = group->cg_item.ci_parent->ci_parent->ci_parent;
+	opts = to_f_uvc_opts(opts_item);
+	pd = &opts->uvc_processing;
+
+	mutex_lock(&opts->lock);
+	if (opts->refcnt) {
+		ret = -EBUSY;
+		goto unlock;
+	}
+
+	ret = __uvcg_iter_item_entries(page, len, __uvcg_count_item_entries, &n,
+				       sizeof(u8));
+	if (ret)
+		goto unlock;
+
+	if (n > pd->bControlSize) {
+		ret = -EINVAL;
+		goto unlock;
+	}
+
+	tmp = bm_controls = kcalloc(n, sizeof(u8), GFP_KERNEL);
+	if (!bm_controls) {
+		ret = -ENOMEM;
+		goto unlock;
+	}
+
+	ret = __uvcg_iter_item_entries(page, len, __uvcg_fill_item_entries, &tmp,
+				       sizeof(u8));
+	if (ret)
+		goto free_mem;
+
+	for (i = 0; i < n; i++)
+		pd->bmControls[i] = bm_controls[i];
+
+	ret = len;
+
+free_mem:
+	kfree(bm_controls);
+unlock:
+	mutex_unlock(&opts->lock);
+	mutex_unlock(su_mutex);
+	return ret;
+}
+
 static ssize_t uvcg_default_processing_bm_controls_show(
 	struct config_item *item, char *page)
 {
···
 	return result;
 }
 
-UVC_ATTR_RO(uvcg_default_processing_, bm_controls, bmControls);
+UVC_ATTR(uvcg_default_processing_, bm_controls, bmControls);
 
 static struct configfs_attribute *uvcg_default_processing_attrs[] = {
 	&uvcg_default_processing_attr_b_unit_id,
···
 
 #undef UVCG_DEFAULT_CAMERA_ATTR
 
+static ssize_t uvcg_default_camera_bm_controls_store(
+	struct config_item *item, const char *page, size_t len)
+{
+	struct config_group *group = to_config_group(item);
+	struct mutex *su_mutex = &group->cg_subsys->su_mutex;
+	struct uvc_camera_terminal_descriptor *cd;
+	struct config_item *opts_item;
+	struct f_uvc_opts *opts;
+	u8 *bm_controls, *tmp;
+	unsigned int i;
+	int ret, n = 0;
+
+	mutex_lock(su_mutex);
+
+	opts_item = group->cg_item.ci_parent->ci_parent->ci_parent->
+			ci_parent;
+	opts = to_f_uvc_opts(opts_item);
+	cd = &opts->uvc_camera_terminal;
+
+	mutex_lock(&opts->lock);
+	if (opts->refcnt) {
+		ret = -EBUSY;
+		goto unlock;
+	}
+
+	ret = __uvcg_iter_item_entries(page, len, __uvcg_count_item_entries, &n,
+				       sizeof(u8));
+	if (ret)
+		goto unlock;
+
+	if (n > cd->bControlSize) {
+		ret = -EINVAL;
+		goto unlock;
+	}
+
+	tmp = bm_controls = kcalloc(n, sizeof(u8), GFP_KERNEL);
+	if (!bm_controls) {
+		ret = -ENOMEM;
+		goto unlock;
+	}
+
+	ret = __uvcg_iter_item_entries(page, len, __uvcg_fill_item_entries, &tmp,
+				       sizeof(u8));
+	if (ret)
+		goto free_mem;
+
+	for (i = 0; i < n; i++)
+		cd->bmControls[i] = bm_controls[i];
+
+	ret = len;
+
+free_mem:
+	kfree(bm_controls);
+unlock:
+	mutex_unlock(&opts->lock);
+	mutex_unlock(su_mutex);
+	return ret;
+}
+
 static ssize_t uvcg_default_camera_bm_controls_show(
 	struct config_item *item, char *page)
 {
···
 	return result;
 }
 
-UVC_ATTR_RO(uvcg_default_camera_, bm_controls, bmControls);
+UVC_ATTR(uvcg_default_camera_, bm_controls, bmControls);
 
 static struct configfs_attribute *uvcg_default_camera_attrs[] = {
 	&uvcg_default_camera_attr_b_terminal_id,