usb: gadget: f_hid: optional SETUP/SET_REPORT mode

f_hid provides the OUT Endpoint as only way for receiving reports
from the host. SETUP/SET_REPORT method is not supported, and this causes
a number of compatibility problems with various host drivers, especially
in the case of keyboard emulation using f_hid.

- Some hosts do not support the OUT Endpoint and ignore it,
so it becomes impossible for the gadget to receive a report
from the host. In the case of a keyboard, the gadget loses
the ability to receive the status of the LEDs.

- Some BIOSes/UEFIs can't work with HID devices with the OUT Endpoint
at all. This may be due to their bugs or incomplete implementation
of the HID standard.
For example, absolutely all Apple UEFIs can't handle the OUT Endpoint
if it goes after IN Endpoint in the descriptor and require the reverse
order (OUT, IN) which is a violation of the standard.
Other hosts either do not initialize gadgets with a descriptor
containing the OUT Endpoint completely (like some HP and DELL BIOSes
and embedded firmwares like on KVM switches), or initialize them,
but will not poll the IN Endpoint.

This patch adds configfs option no_out_endpoint=1 to disable
the OUT Endpoint and allows f_hid to receive reports from the host
via SETUP/SET_REPORT.

Previously, there was such a feature in f_hid, but it was replaced
by the OUT Endpoint [1] in the commit 99c515005857 ("usb: gadget: hidg:
register OUT INT endpoint for SET_REPORT"). So this patch actually
returns the removed functionality while making it optional.
For backward compatibility reasons, the OUT Endpoint mode remains
the default behaviour.

- The OUT Endpoint mode provides the report queue and reduces
USB overhead (eliminating SETUP routine) on transmitting a report
from the host.

- If the SETUP/SET_REPORT mode is used, there is no report queue,
so the userspace will only read last report. For classic HID devices
like keyboards this is not a problem, since it's intended to transmit
the status of the LEDs and only the last report is important.
This mode provides better compatibility with strange and buggy
host drivers.

Both modes passed USBCV tests. Checking with the USB protocol analyzer
also confirmed that everything is working as it should and the new mode
ensures operability in all of the described cases.

Link: https://www.spinics.net/lists/linux-usb/msg65494.html [1]
Reviewed-by: Maciej Żenczykowski <[e-mail]>
Acked-by: Felipe Balbi <[e-mail]>
Signed-off-by: Maxim Devaev <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/gadget/function/f_hid.c

···
 	unsigned short			report_desc_length;
 	char				*report_desc;
 	unsigned short			report_length;
+	/*
+	 * use_out_ep - if true, the OUT Endpoint (interrupt out method)
+	 *              will be used to receive reports from the host
+	 *              using functions with the "intout" suffix.
+	 *              Otherwise, the OUT Endpoint will not be configured
+	 *              and the SETUP/SET_REPORT method ("ssreport" suffix)
+	 *              will be used to receive reports.
+	 */
+	bool				use_out_ep;
 
 	/* recv report */
-	struct list_head		completed_out_req;
 	spinlock_t			read_spinlock;
 	wait_queue_head_t		read_queue;
+	/* recv report - interrupt out only (use_out_ep == 1) */
+	struct list_head		completed_out_req;
 	unsigned int			qlen;
+	/* recv report - setup set_report only (use_out_ep == 0) */
+	char				*set_report_buf;
+	unsigned int			set_report_length;
 
 	/* send report */
 	spinlock_t			write_spinlock;
···
 	.bDescriptorType	= USB_DT_INTERFACE,
 	/* .bInterfaceNumber	= DYNAMIC */
 	.bAlternateSetting	= 0,
-	.bNumEndpoints		= 2,
+	/* .bNumEndpoints	= DYNAMIC (depends on use_out_ep) */
 	.bInterfaceClass	= USB_CLASS_HID,
 	/* .bInterfaceSubClass	= DYNAMIC */
 	/* .bInterfaceProtocol	= DYNAMIC */
···
 	/* .wBytesPerInterval   = DYNAMIC */
 };
 
-static struct usb_descriptor_header *hidg_ss_descriptors[] = {
+static struct usb_descriptor_header *hidg_ss_descriptors_intout[] = {
 	(struct usb_descriptor_header *)&hidg_interface_desc,
 	(struct usb_descriptor_header *)&hidg_desc,
 	(struct usb_descriptor_header *)&hidg_ss_in_ep_desc,
 	(struct usb_descriptor_header *)&hidg_ss_in_comp_desc,
 	(struct usb_descriptor_header *)&hidg_ss_out_ep_desc,
 	(struct usb_descriptor_header *)&hidg_ss_out_comp_desc,
+	NULL,
+};
+
+static struct usb_descriptor_header *hidg_ss_descriptors_ssreport[] = {
+	(struct usb_descriptor_header *)&hidg_interface_desc,
+	(struct usb_descriptor_header *)&hidg_desc,
+	(struct usb_descriptor_header *)&hidg_ss_in_ep_desc,
+	(struct usb_descriptor_header *)&hidg_ss_in_comp_desc,
 	NULL,
 };
 
···
 				      */
 };
 
-static struct usb_descriptor_header *hidg_hs_descriptors[] = {
+static struct usb_descriptor_header *hidg_hs_descriptors_intout[] = {
 	(struct usb_descriptor_header *)&hidg_interface_desc,
 	(struct usb_descriptor_header *)&hidg_desc,
 	(struct usb_descriptor_header *)&hidg_hs_in_ep_desc,
 	(struct usb_descriptor_header *)&hidg_hs_out_ep_desc,
+	NULL,
+};
+
+static struct usb_descriptor_header *hidg_hs_descriptors_ssreport[] = {
+	(struct usb_descriptor_header *)&hidg_interface_desc,
+	(struct usb_descriptor_header *)&hidg_desc,
+	(struct usb_descriptor_header *)&hidg_hs_in_ep_desc,
 	NULL,
 };
 
···
 				       */
 };
 
-static struct usb_descriptor_header *hidg_fs_descriptors[] = {
+static struct usb_descriptor_header *hidg_fs_descriptors_intout[] = {
 	(struct usb_descriptor_header *)&hidg_interface_desc,
 	(struct usb_descriptor_header *)&hidg_desc,
 	(struct usb_descriptor_header *)&hidg_fs_in_ep_desc,
 	(struct usb_descriptor_header *)&hidg_fs_out_ep_desc,
+	NULL,
+};
+
+static struct usb_descriptor_header *hidg_fs_descriptors_ssreport[] = {
+	(struct usb_descriptor_header *)&hidg_interface_desc,
+	(struct usb_descriptor_header *)&hidg_desc,
+	(struct usb_descriptor_header *)&hidg_fs_in_ep_desc,
 	NULL,
 };
 
···
 /*-------------------------------------------------------------------------*/
 /*                              Char Device                                */
 
-static ssize_t f_hidg_read(struct file *file, char __user *buffer,
-			size_t count, loff_t *ptr)
+static ssize_t f_hidg_intout_read(struct file *file, char __user *buffer,
+				  size_t count, loff_t *ptr)
 {
 	struct f_hidg *hidg = file->private_data;
 	struct f_hidg_req_list *list;
···
 
 	spin_lock_irqsave(&hidg->read_spinlock, flags);
 
-#define READ_COND (!list_empty(&hidg->completed_out_req))
+#define READ_COND_INTOUT (!list_empty(&hidg->completed_out_req))
 
 	/* wait for at least one buffer to complete */
-	while (!READ_COND) {
+	while (!READ_COND_INTOUT) {
 		spin_unlock_irqrestore(&hidg->read_spinlock, flags);
 		if (file->f_flags & O_NONBLOCK)
 			return -EAGAIN;
 
-		if (wait_event_interruptible(hidg->read_queue, READ_COND))
+		if (wait_event_interruptible(hidg->read_queue, READ_COND_INTOUT))
 			return -ERESTARTSYS;
 
 		spin_lock_irqsave(&hidg->read_spinlock, flags);
···
 	}
 
 	return count;
+}
+
+#define READ_COND_SSREPORT (hidg->set_report_buf != NULL)
+
+static ssize_t f_hidg_ssreport_read(struct file *file, char __user *buffer,
+				    size_t count, loff_t *ptr)
+{
+	struct f_hidg *hidg = file->private_data;
+	char *tmp_buf = NULL;
+	unsigned long flags;
+
+	if (!count)
+		return 0;
+
+	spin_lock_irqsave(&hidg->read_spinlock, flags);
+
+	while (!READ_COND_SSREPORT) {
+		spin_unlock_irqrestore(&hidg->read_spinlock, flags);
+		if (file->f_flags & O_NONBLOCK)
+			return -EAGAIN;
+
+		if (wait_event_interruptible(hidg->read_queue, READ_COND_SSREPORT))
+			return -ERESTARTSYS;
+
+		spin_lock_irqsave(&hidg->read_spinlock, flags);
+	}
+
+	count = min_t(unsigned int, count, hidg->set_report_length);
+	tmp_buf = hidg->set_report_buf;
+	hidg->set_report_buf = NULL;
+
+	spin_unlock_irqrestore(&hidg->read_spinlock, flags);
+
+	if (tmp_buf != NULL) {
+		count -= copy_to_user(buffer, tmp_buf, count);
+		kfree(tmp_buf);
+	} else {
+		count = -ENOMEM;
+	}
+
+	wake_up(&hidg->read_queue);
+
+	return count;
+}
+
+static ssize_t f_hidg_read(struct file *file, char __user *buffer,
+			   size_t count, loff_t *ptr)
+{
+	struct f_hidg *hidg = file->private_data;
+
+	if (hidg->use_out_ep)
+		return f_hidg_intout_read(file, buffer, count, ptr);
+	else
+		return f_hidg_ssreport_read(file, buffer, count, ptr);
 }
 
 static void f_hidg_req_complete(struct usb_ep *ep, struct usb_request *req)
···
 	if (WRITE_COND)
 		ret |= EPOLLOUT | EPOLLWRNORM;
 
-	if (READ_COND)
-		ret |= EPOLLIN | EPOLLRDNORM;
+	if (hidg->use_out_ep) {
+		if (READ_COND_INTOUT)
+			ret |= EPOLLIN | EPOLLRDNORM;
+	} else {
+		if (READ_COND_SSREPORT)
+			ret |= EPOLLIN | EPOLLRDNORM;
+	}
 
 	return ret;
 }
 
 #undef WRITE_COND
-#undef READ_COND
+#undef READ_COND_SSREPORT
+#undef READ_COND_INTOUT
 
 static int f_hidg_release(struct inode *inode, struct file *fd)
 {
···
 	return alloc_ep_req(ep, length);
 }
 
-static void hidg_set_report_complete(struct usb_ep *ep, struct usb_request *req)
+static void hidg_intout_complete(struct usb_ep *ep, struct usb_request *req)
 {
 	struct f_hidg *hidg = (struct f_hidg *) req->context;
 	struct usb_composite_dev *cdev = hidg->func.config->cdev;
···
 		free_ep_req(ep, req);
 		return;
 	}
+}
+
+static void hidg_ssreport_complete(struct usb_ep *ep, struct usb_request *req)
+{
+	struct f_hidg *hidg = (struct f_hidg *)req->context;
+	struct usb_composite_dev *cdev = hidg->func.config->cdev;
+	char *new_buf = NULL;
+	unsigned long flags;
+
+	if (req->status != 0 || req->buf == NULL || req->actual == 0) {
+		ERROR(cdev,
+		      "%s FAILED: status=%d, buf=%p, actual=%d\n",
+		      __func__, req->status, req->buf, req->actual);
+		return;
+	}
+
+	spin_lock_irqsave(&hidg->read_spinlock, flags);
+
+	new_buf = krealloc(hidg->set_report_buf, req->actual, GFP_ATOMIC);
+	if (new_buf == NULL) {
+		spin_unlock_irqrestore(&hidg->read_spinlock, flags);
+		return;
+	}
+	hidg->set_report_buf = new_buf;
+
+	hidg->set_report_length = req->actual;
+	memcpy(hidg->set_report_buf, req->buf, req->actual);
+
+	spin_unlock_irqrestore(&hidg->read_spinlock, flags);
+
+	wake_up(&hidg->read_queue);
 }
 
 static int hidg_setup(struct usb_function *f,
···
 	case ((USB_DIR_OUT | USB_TYPE_CLASS | USB_RECIP_INTERFACE) << 8
 		  | HID_REQ_SET_REPORT):
 		VDBG(cdev, "set_report | wLength=%d\n", ctrl->wLength);
-		goto stall;
+		if (hidg->use_out_ep)
+			goto stall;
+		req->complete = hidg_ssreport_complete;
+		req->context  = hidg;
+		goto respond;
 		break;
 
 	case ((USB_DIR_OUT | USB_TYPE_CLASS | USB_RECIP_INTERFACE) << 8
···
 	unsigned long flags;
 
 	usb_ep_disable(hidg->in_ep);
-	usb_ep_disable(hidg->out_ep);
 
-	spin_lock_irqsave(&hidg->read_spinlock, flags);
-	list_for_each_entry_safe(list, next, &hidg->completed_out_req, list) {
-		free_ep_req(hidg->out_ep, list->req);
-		list_del(&list->list);
-		kfree(list);
+	if (hidg->out_ep) {
+		usb_ep_disable(hidg->out_ep);
+
+		spin_lock_irqsave(&hidg->read_spinlock, flags);
+		list_for_each_entry_safe(list, next, &hidg->completed_out_req, list) {
+			free_ep_req(hidg->out_ep, list->req);
+			list_del(&list->list);
+			kfree(list);
+		}
+		spin_unlock_irqrestore(&hidg->read_spinlock, flags);
 	}
-	spin_unlock_irqrestore(&hidg->read_spinlock, flags);
 
 	spin_lock_irqsave(&hidg->write_spinlock, flags);
 	if (!hidg->write_pending) {
···
 		}
 	}
 
-
-	if (hidg->out_ep != NULL) {
+	if (hidg->use_out_ep && hidg->out_ep != NULL) {
 		/* restart endpoint */
 		usb_ep_disable(hidg->out_ep);
 
···
 					hidg_alloc_ep_req(hidg->out_ep,
 							  hidg->report_length);
 			if (req) {
-				req->complete = hidg_set_report_complete;
+				req->complete = hidg_intout_complete;
 				req->context  = hidg;
 				status = usb_ep_queue(hidg->out_ep, req,
 						      GFP_ATOMIC);
···
 	}
 	return 0;
 disable_out_ep:
-	usb_ep_disable(hidg->out_ep);
+	if (hidg->out_ep)
+		usb_ep_disable(hidg->out_ep);
 free_req_in:
 	if (req_in)
 		free_ep_req(hidg->in_ep, req_in);
···
 		goto fail;
 	hidg->in_ep = ep;
 
-	ep = usb_ep_autoconfig(c->cdev->gadget, &hidg_fs_out_ep_desc);
-	if (!ep)
-		goto fail;
-	hidg->out_ep = ep;
+	hidg->out_ep = NULL;
+	if (hidg->use_out_ep) {
+		ep = usb_ep_autoconfig(c->cdev->gadget, &hidg_fs_out_ep_desc);
+		if (!ep)
+			goto fail;
+		hidg->out_ep = ep;
+	}
+
+	/* used only if use_out_ep == 1 */
+	hidg->set_report_buf = NULL;
 
 	/* set descriptor dynamic values */
 	hidg_interface_desc.bInterfaceSubClass = hidg->bInterfaceSubClass;
 	hidg_interface_desc.bInterfaceProtocol = hidg->bInterfaceProtocol;
+	hidg_interface_desc.bNumEndpoints = hidg->use_out_ep ? 2 : 1;
 	hidg->protocol = HID_REPORT_PROTOCOL;
 	hidg->idle = 1;
 	hidg_ss_in_ep_desc.wMaxPacketSize = cpu_to_le16(hidg->report_length);
···
 	hidg_ss_out_ep_desc.bEndpointAddress =
 		hidg_fs_out_ep_desc.bEndpointAddress;
 
-	status = usb_assign_descriptors(f, hidg_fs_descriptors,
-			hidg_hs_descriptors, hidg_ss_descriptors,
-			hidg_ss_descriptors);
+	if (hidg->use_out_ep)
+		status = usb_assign_descriptors(f,
+			hidg_fs_descriptors_intout,
+			hidg_hs_descriptors_intout,
+			hidg_ss_descriptors_intout,
+			hidg_ss_descriptors_intout);
+	else
+		status = usb_assign_descriptors(f,
+			hidg_fs_descriptors_ssreport,
+			hidg_hs_descriptors_ssreport,
+			hidg_ss_descriptors_ssreport,
+			hidg_ss_descriptors_ssreport);
+
 	if (status)
 		goto fail;
 
···
 
 F_HID_OPT(subclass, 8, 255);
 F_HID_OPT(protocol, 8, 255);
+F_HID_OPT(no_out_endpoint, 8, 1);
 F_HID_OPT(report_length, 16, 65535);
 
 static ssize_t f_hid_opts_report_desc_show(struct config_item *item, char *page)
···
 static struct configfs_attribute *hid_attrs[] = {
 	&f_hid_opts_attr_subclass,
 	&f_hid_opts_attr_protocol,
+	&f_hid_opts_attr_no_out_endpoint,
 	&f_hid_opts_attr_report_length,
 	&f_hid_opts_attr_report_desc,
 	&f_hid_opts_attr_dev,
···
 	hidg = func_to_hidg(f);
 	opts = container_of(f->fi, struct f_hid_opts, func_inst);
 	kfree(hidg->report_desc);
+	kfree(hidg->set_report_buf);
 	kfree(hidg);
 	mutex_lock(&opts->lock);
 	--opts->refcnt;
···
 			return ERR_PTR(-ENOMEM);
 		}
 	}
+	hidg->use_out_ep = !opts->no_out_endpoint;
 
 	mutex_unlock(&opts->lock);
 

drivers/usb/gadget/function/u_hid.h

···
 	int				minor;
 	unsigned char			subclass;
 	unsigned char			protocol;
+	unsigned char			no_out_endpoint;
 	unsigned short			report_length;
 	unsigned short			report_desc_length;
 	unsigned char			*report_desc;