[PATCH v2] usb: gadget: f_fs: Add the missing get_alt callback

[Hardik Gajjar]

The Apple CarLife iAP gadget has a descriptor with two alternate
settings. The host sends the set_alt request to configure alt_setting
0 or 1, and this is verified by the subsequent get_alt request.

This patch implements and sets the get_alt callback. Without the
get_alt callback, composite.c abruptly concludes the
USB_REQ_GET/SET_INTERFACE request, assuming only one alt setting
for the endpoint.

Signed-off-by: Hardik Gajjar <hgajjar@xxxxxxxxxxxxxx>
---
changes since version 1:
	- improve commit message to indicate why the get_alt callback
	  is necessary
	- Link to v1 - https://lore.kernel.org/all/20231124164435.74727-1-hgajjar@xxxxxxxxxxxxxx/
---
 drivers/usb/gadget/function/f_fs.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
index efe3e3b85769..37c47c11f57a 100644
--- a/drivers/usb/gadget/function/f_fs.c
+++ b/drivers/usb/gadget/function/f_fs.c
@@ -75,6 +75,7 @@ struct ffs_function {
 	short				*interfaces_nums;
 
 	struct usb_function		function;
+	int				cur_alt[MAX_CONFIG_INTERFACES];
 };
 
 
@@ -98,6 +99,7 @@ static int __must_check ffs_func_eps_enable(struct ffs_function *func);
 static int ffs_func_bind(struct usb_configuration *,
 			 struct usb_function *);
 static int ffs_func_set_alt(struct usb_function *, unsigned, unsigned);
+static int ffs_func_get_alt(struct usb_function *f, unsigned int intf);
 static void ffs_func_disable(struct usb_function *);
 static int ffs_func_setup(struct usb_function *,
 			  const struct usb_ctrlrequest *);
@@ -3232,6 +3234,15 @@ static void ffs_reset_work(struct work_struct *work)
 	ffs_data_reset(ffs);
 }
 
+static int ffs_func_get_alt(struct usb_function *f,
+			    unsigned int interface)
+{
+	struct ffs_function *func = ffs_func_from_usb(f);
+	int intf = ffs_func_revmap_intf(func, interface);
+
+	return (intf < 0) ? intf : func->cur_alt[interface];
+}
+
 static int ffs_func_set_alt(struct usb_function *f,
 			    unsigned interface, unsigned alt)
 {
@@ -3266,8 +3277,10 @@ static int ffs_func_set_alt(struct usb_function *f,
 
 	ffs->func = func;
 	ret = ffs_func_eps_enable(func);
-	if (ret >= 0)
+	if (ret >= 0) {
 		ffs_event_add(ffs, FUNCTIONFS_ENABLE);
+		func->cur_alt[interface] = alt;
+	}
 	return ret;
 }
 
@@ -3574,6 +3587,7 @@ static struct usb_function *ffs_alloc(struct usb_function_instance *fi)
 	func->function.bind    = ffs_func_bind;
 	func->function.unbind  = ffs_func_unbind;
 	func->function.set_alt = ffs_func_set_alt;
+	func->function.get_alt = ffs_func_get_alt;
 	func->function.disable = ffs_func_disable;
 	func->function.setup   = ffs_func_setup;
 	func->function.req_match = ffs_func_req_match;
-- 
2.17.1