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, 24 insertions, 0 deletions

diff --git a/drivers/usb/gadget/function/u_fs.h b/drivers/usb/gadget/function/u_fs.h
index cd128e31f80..284a1f00a98 100644
--- a/drivers/usb/gadget/function/u_fs.h
+++ b/drivers/usb/gadget/function/u_fs.h
@@ -19,6 +19,7 @@
 #include <linux/usb/composite.h>
 #include <linux/list.h>
 #include <linux/mutex.h>
+#include <linux/workqueue.h>
 
 #ifdef VERBOSE_DEBUG
 #ifndef pr_vdebug
@@ -93,6 +94,26 @@ enum ffs_state {
 	FFS_ACTIVE,
 
 	/*
+	 * Function is visible to host, but it's not functional. All
+	 * setup requests are stalled and transfers on another endpoints
+	 * are refused. All epfiles, except ep0, are deleted so there
+	 * is no way to perform any operations on them.
+	 *
+	 * This state is set after closing all functionfs files, when
+	 * mount parameter "no_disconnect=1" has been set. Function will
+	 * remain in deactivated state until filesystem is umounted or
+	 * ep0 is opened again. In the second case functionfs state will
+	 * be reset, and it will be ready for descriptors and strings
+	 * writing.
+	 *
+	 * This is useful only when functionfs is composed to gadget
+	 * with another function which can perform some critical
+	 * operations, and it's strongly desired to have this operations
+	 * completed, even after functionfs files closure.
+	 */
+	FFS_DEACTIVATED,
+
+	/*
 	 * All endpoints have been closed.  This state is also set if
 	 * we encounter an unrecoverable error.  The only
 	 * unrecoverable error is situation when after reading strings
@@ -251,6 +272,9 @@ struct ffs_data {
 		kgid_t				gid;
 	}				file_perms;
 
+	bool no_disconnect;
+	struct work_struct reset_work;
+
 	/*
 	 * The endpoint files, filled by ffs_epfiles_create(),
 	 * destroyed by ffs_epfiles_destroy().