usb: gadget: f_fs: add "no_disconnect" mode

Since we can compose gadgets from many functions, there is the problem
related to gadget breakage while FunctionFS daemon being closed. FFS
function is userspace code so there is no way to know when it will close
files (it doesn't matter what is the reason of this situation, it can
be daemon logic, program breakage, process kill or any other). So when
we have another function in gadget which, for example, sends some amount
of data, does some software update or implements some real-time functionality,
we may want to keep the gadget connected despite FFS function is no longer
functional.

We can't just remove one of functions from gadget since it has been
enumerated, so the only way to keep entire gadget working is to make
broken FFS function deactivated but still visible to host. For this
purpose this patch introduces "no_disconnect" mode. It can be enabled
by setting mount option "no_disconnect=1", and results with defering
function disconnect to the moment of reopen ep0 file or filesystem
unmount. After closing all endpoint files, FunctionFS is set to state
FFS_DEACTIVATED.

When ffs->state == FFS_DEACTIVATED:
- function is still bound and visible to host,
- setup requests are automatically stalled,
- transfers on other endpoints are refused,
- epfiles, except ep0, are deleted from the filesystem,
- opening ep0 causes the function to be closed, and then FunctionFS
  is ready for descriptors and string write,
- altsetting change causes the function to be closed - we want to keep
  function alive until another functions are potentialy used, altsetting
  change means that another configuration is being selected or USB cable
  was unplugged, which indicates that we don't need to stay longer in
  FFS_DEACTIVATED state
- unmounting of the FunctionFS instance causes the function to be closed.

Tested-by: David Cohen <david.a.cohen@linux.intel.com>
Acked-by: Michal Nazarewicz <mina86@mina86.com>
Signed-off-by: Robert Baldyga <r.baldyga@samsung.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

1 files changed, 51 insertions, 5 deletions

diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
index a00ee977305c..e78a2c6af8d3 100644
--- a/drivers/usb/gadget/function/f_fs.c
+++ b/drivers/usb/gadget/function/f_fs.c
@@ -605,6 +605,8 @@ static unsigned int ffs_ep0_poll(struct file *file, poll_table *wait)
 		}
 	case FFS_CLOSING:
 		break;
+	case FFS_DEACTIVATED:
+		break;
 	}
 
 	mutex_unlock(&ffs->mutex);
@@ -1179,6 +1181,7 @@ struct ffs_sb_fill_data {
 	struct ffs_file_perms perms;
 	umode_t root_mode;
 	const char *dev_name;
+	bool no_disconnect;
 	struct ffs_data *ffs_data;
 };
 
@@ -1249,6 +1252,12 @@ static int ffs_fs_parse_opts(struct ffs_sb_fill_data *data, char *opts)
 
 		/* Interpret option */
 		switch (eq - opts) {
+		case 13:
+			if (!memcmp(opts, "no_disconnect", 13))
+				data->no_disconnect = !!value;
+			else
+				goto invalid;
+			break;
 		case 5:
 			if (!memcmp(opts, "rmode", 5))
 				data->root_mode  = (value & 0555) | S_IFDIR;
@@ -1313,6 +1322,7 @@ ffs_fs_mount(struct file_system_type *t, int flags,
 			.gid = GLOBAL_ROOT_GID,
 		},
 		.root_mode = S_IFDIR | 0500,
+		.no_disconnect = false,
 	};
 	struct dentry *rv;
 	int ret;
@@ -1329,6 +1339,7 @@ ffs_fs_mount(struct file_system_type *t, int flags,
 	if (unlikely(!ffs))
 		return ERR_PTR(-ENOMEM);
 	ffs->file_perms = data.perms;
+	ffs->no_disconnect = data.no_disconnect;
 
 	ffs->dev_name = kstrdup(dev_name, GFP_KERNEL);
 	if (unlikely(!ffs->dev_name)) {
@@ -1360,6 +1371,7 @@ ffs_fs_kill_sb(struct super_block *sb)
 	kill_litter_super(sb);
 	if (sb->s_fs_info) {
 		ffs_release_dev(sb->s_fs_info);
+		ffs_data_closed(sb->s_fs_info);
 		ffs_data_put(sb->s_fs_info);
 	}
 }
@@ -1416,7 +1428,11 @@ static void ffs_data_opened(struct ffs_data *ffs)
 	ENTER();
 
 	atomic_inc(&ffs->ref);
-	atomic_inc(&ffs->opened);
+	if (atomic_add_return(1, &ffs->opened) == 1 &&
+			ffs->state == FFS_DEACTIVATED) {
+		ffs->state = FFS_CLOSING;
+		ffs_data_reset(ffs);
+	}
 }
 
 static void ffs_data_put(struct ffs_data *ffs)
@@ -1438,6 +1454,21 @@ static void ffs_data_closed(struct ffs_data *ffs)
 	ENTER();
 
 	if (atomic_dec_and_test(&ffs->opened)) {
+		if (ffs->no_disconnect) {
+			ffs->state = FFS_DEACTIVATED;
+			if (ffs->epfiles) {
+				ffs_epfiles_destroy(ffs->epfiles,
+						   ffs->eps_count);
+				ffs->epfiles = NULL;
+			}
+			if (ffs->setup_state == FFS_SETUP_PENDING)
+				__ffs_ep0_stall(ffs);
+		} else {
+			ffs->state = FFS_CLOSING;
+			ffs_data_reset(ffs);
+		}
+	}
+	if (atomic_read(&ffs->opened) < 0) {
 		ffs->state = FFS_CLOSING;
 		ffs_data_reset(ffs);
 	}
@@ -1615,7 +1646,6 @@ static void ffs_epfiles_destroy(struct ffs_epfile *epfiles, unsigned count)
 	kfree(epfiles);
 }
 
-
 static void ffs_func_eps_disable(struct ffs_function *func)
 {
 	struct ffs_ep *ep         = func->eps;
@@ -1628,10 +1658,12 @@ static void ffs_func_eps_disable(struct ffs_function *func)
 		/* pending requests get nuked */
 		if (likely(ep->ep))
 			usb_ep_disable(ep->ep);
-		epfile->ep = NULL;
-
 		++ep;
-		++epfile;
+
+		if (epfile) {
+			epfile->ep = NULL;
+			++epfile;
+		}
 	} while (--count);
 	spin_unlock_irqrestore(&func->ffs->eps_lock, flags);
 }
@@ -2894,6 +2926,13 @@ static int ffs_func_bind(struct usb_configuration *c,
 
 /* Other USB function hooks *************************************************/
 
+static void ffs_reset_work(struct work_struct *work)
+{
+	struct ffs_data *ffs = container_of(work,
+		struct ffs_data, reset_work);
+	ffs_data_reset(ffs);
+}
+
 static int ffs_func_set_alt(struct usb_function *f,
 			    unsigned interface, unsigned alt)
 {
@@ -2910,6 +2949,13 @@ static int ffs_func_set_alt(struct usb_function *f,
 	if (ffs->func)
 		ffs_func_eps_disable(ffs->func);
 
+	if (ffs->state == FFS_DEACTIVATED) {
+		ffs->state = FFS_CLOSING;
+		INIT_WORK(&ffs->reset_work, ffs_reset_work);
+		schedule_work(&ffs->reset_work);
+		return -ENODEV;
+	}
+
 	if (ffs->state != FFS_ACTIVE)
 		return -ENODEV;