usb: gadget: ffs: add eventfd notification about ffs events

Add eventfd which notifies userspace about ep0 events and AIO completion
events. It simplifies using of FunctionFS with event loop, because now
we need to poll on single file (instead of polling on ep0 and eventfd's
supplied to AIO layer).

FunctionFS eventfd is not triggered if another eventfd is supplied to
AIO layer (in AIO request). It can be useful, for example, when we want
to handle AIO transations for chosen endpoint in separate thread.

Signed-off-by: Robert Baldyga <[e-mail]>
Acked-by: Michal Nazarewicz <[e-mail]>
Signed-off-by: Felipe Balbi <[e-mail]>

drivers/usb/gadget/function/f_fs.c

···
 #include <linux/aio.h>
 #include <linux/mmu_context.h>
 #include <linux/poll.h>
+#include <linux/eventfd.h>
 
 #include "u_fs.h"
 #include "u_f.h"
···
 
 	struct usb_ep *ep;
 	struct usb_request *req;
+
+	struct ffs_data *ffs;
 };
 
 struct ffs_desc_helper {
···
 
 	aio_complete(io_data->kiocb, ret, ret);
 
+	if (io_data->ffs->ffs_eventfd && !io_data->kiocb->ki_eventfd)
+		eventfd_signal(io_data->ffs->ffs_eventfd, 1);
+
 	usb_ep_free_request(io_data->ep, io_data->req);
 
 	io_data->kiocb->private = NULL;
···
 			io_data->buf = data;
 			io_data->ep = ep->ep;
 			io_data->req = req;
+			io_data->ffs = epfile->ffs;
 
 			req->context  = io_data;
 			req->complete = ffs_epfile_async_io_complete;
···
 	if (ffs->epfiles)
 		ffs_epfiles_destroy(ffs->epfiles, ffs->eps_count);
 
+	if (ffs->ffs_eventfd)
+		eventfd_ctx_put(ffs->ffs_eventfd);
+
 	kfree(ffs->raw_descs_data);
 	kfree(ffs->raw_strings);
 	kfree(ffs->stringtabs);
···
 			      FUNCTIONFS_HAS_HS_DESC |
 			      FUNCTIONFS_HAS_SS_DESC |
 			      FUNCTIONFS_HAS_MS_OS_DESC |
-			      FUNCTIONFS_VIRTUAL_ADDR)) {
+			      FUNCTIONFS_VIRTUAL_ADDR |
+			      FUNCTIONFS_EVENTFD)) {
 			ret = -ENOSYS;
 			goto error;
 		}
···
 		break;
 	default:
 		goto error;
+	}
+
+	if (flags & FUNCTIONFS_EVENTFD) {
+		if (len < 4)
+			goto error;
+		ffs->ffs_eventfd =
+			eventfd_ctx_fdget((int)get_unaligned_le32(data));
+		if (IS_ERR(ffs->ffs_eventfd)) {
+			ret = PTR_ERR(ffs->ffs_eventfd);
+			ffs->ffs_eventfd = NULL;
+			goto error;
+		}
+		data += 4;
+		len  -= 4;
 	}
 
 	/* Read fs_count, hs_count and ss_count (if present) */
···
 	pr_vdebug("adding event %d\n", type);
 	ffs->ev.types[ffs->ev.count++] = type;
 	wake_up_locked(&ffs->ev.waitq);
+	if (ffs->ffs_eventfd)
+		eventfd_signal(ffs->ffs_eventfd, 1);
 }
 
 static void ffs_event_add(struct ffs_data *ffs,

drivers/usb/gadget/function/u_fs.h

···
 		kgid_t				gid;
 	}				file_perms;
 
+	struct eventfd_ctx *ffs_eventfd;
 	bool no_disconnect;
 	struct work_struct reset_work;
 

include/uapi/linux/usb/functionfs.h

···
 	FUNCTIONFS_HAS_SS_DESC = 4,
 	FUNCTIONFS_HAS_MS_OS_DESC = 8,
 	FUNCTIONFS_VIRTUAL_ADDR = 16,
+	FUNCTIONFS_EVENTFD = 32,
 };
 
 /* Descriptor of an non-audio endpoint */