linux-kernel - [PATCH v1] USB: gadget: core: create sysfs link between udc and gadget

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Message-ID: <20240307030922.3573161-1-royluo@google.com>
Date: Thu,  7 Mar 2024 03:09:22 +0000
From: Roy Luo <royluo@...gle.com>
To: royluo@...gle.com, gregkh@...uxfoundation.org, stern@...land.harvard.edu, 
	badhri@...gle.com, quic_kriskura@...cinc.com, francesco.dolcini@...adex.com, 
	quic_eserrao@...cinc.com, ivan.orlov0322@...il.com, linux-usb@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: [PATCH v1] USB: gadget: core: create sysfs link between udc and gadget

udc device and gadget device are tightly coupled, yet there's no good
way to corelate the two. Add a sysfs link in udc that points to the
corresponding gadget device.
An example use case: userspace configures a f_midi configfs driver and
bind the udc device, then it tries to locate the corresponding midi
device, which is a child device of the gadget device. The gadget device
that's associated to the udc device has to be identified in order to
index the midi device. Having a sysfs link would make things much
easier.

Signed-off-by: Roy Luo <royluo@...gle.com>
---
 drivers/usb/gadget/udc/core.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/usb/gadget/udc/core.c b/drivers/usb/gadget/udc/core.c
index d59f94464b87..876b8635b16f 100644
--- a/drivers/usb/gadget/udc/core.c
+++ b/drivers/usb/gadget/udc/core.c
@@ -1419,8 +1419,16 @@ int usb_add_gadget(struct usb_gadget *gadget)
 	if (ret)
 		goto err_free_id;
 
+	ret = sysfs_create_link(&udc->dev.kobj,
+				&gadget->dev.kobj, "gadget");
+	if (ret)
+		goto err_del_gadget;
+
 	return 0;
 
+ err_del_gadget:
+	device_del(&gadget->dev);
+
  err_free_id:
 	ida_free(&gadget_id_numbers, gadget->id_number);
 
@@ -1529,6 +1537,7 @@ void usb_del_gadget(struct usb_gadget *gadget)
 	mutex_unlock(&udc_lock);
 
 	kobject_uevent(&udc->dev.kobj, KOBJ_REMOVE);
+	sysfs_remove_link(&udc->dev.kobj, "gadget");
 	flush_work(&gadget->work);
 	device_del(&gadget->dev);
 	ida_free(&gadget_id_numbers, gadget->id_number);

base-commit: 67be068d31d423b857ffd8c34dbcc093f8dfff76
-- 
2.44.0.278.ge034bb2e1d-goog