linux-kernel - [PATCH v2] HID: logitech-dj: issue udev change event on device connection

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Date:   Wed, 18 Mar 2020 19:27:21 +0000
From:   Filipe Laíns <lains@...hlinux.org>
To:     Jiri Kosina <jikos@...nel.org>,
        Benjamin Tissoires <benjamin.tissoires@...hat.com>,
        linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
        Peter Hutterer <peter.hutterer@...hat.com>,
        Hans de Goede <hdegoede@...hat.com>,
        Mario Limonciello <superm1@...il.com>,
        Richard Hughes <hughsient@...il.com>
Cc:     Filipe Laíns <lains@...hlinux.org>
Subject: [PATCH v2] HID: logitech-dj: issue udev change event on device connection

As discussed in the mailing list:

> Right now the hid-logitech-dj driver will export one node for each
> connected device, even when the device is not connected. That causes
> some trouble because in userspace we don't have have any way to know if
> the device is connected or not, so when we try to communicate, if the
> device is disconnected it will fail.

The solution reached to solve this issue is to trigger an udev change
event when the device connects, this way userspace can just wait on
those connections instead of trying to ping the device.

Signed-off-by: Filipe Laíns <lains@...hlinux.org>

---

v2:
  - Issue udev change event on the connected hid device, not on the
  receiver

---
 drivers/hid/hid-logitech-dj.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/hid/hid-logitech-dj.c b/drivers/hid/hid-logitech-dj.c
index 48dff5d6b605..282e57dd467d 100644
--- a/drivers/hid/hid-logitech-dj.c
+++ b/drivers/hid/hid-logitech-dj.c
@@ -1412,6 +1412,7 @@ static int logi_dj_dj_event(struct hid_device *hdev,
 {
 	struct dj_receiver_dev *djrcv_dev = hid_get_drvdata(hdev);
 	struct dj_report *dj_report = (struct dj_report *) data;
+	struct dj_device *dj_dev;
 	unsigned long flags;
 
 	/*
@@ -1447,7 +1448,9 @@ static int logi_dj_dj_event(struct hid_device *hdev,
 
 	spin_lock_irqsave(&djrcv_dev->lock, flags);
 
-	if (!djrcv_dev->paired_dj_devices[dj_report->device_index]) {
+	dj_dev = djrcv_dev->paired_dj_devices[dj_report->device_index];
+
+	if (!dj_dev) {
 		/* received an event for an unknown device, bail out */
 		logi_dj_recv_queue_notification(djrcv_dev, dj_report);
 		goto out;
@@ -1464,6 +1467,8 @@ static int logi_dj_dj_event(struct hid_device *hdev,
 		if (dj_report->report_params[CONNECTION_STATUS_PARAM_STATUS] ==
 		    STATUS_LINKLOSS) {
 			logi_dj_recv_forward_null_report(djrcv_dev, dj_report);
+		} else {
+			kobject_uevent(&dj_dev->hdev->dev.kobj, KOBJ_CHANGE);
 		}
 		break;
 	default:
-- 
2.25.1