On Tue, 2020-03-24 at 15:03 +0100, Bastien Nocera wrote:

On Tue, 2020-03-24 at 13:46 +0000, Filipe Laíns wrote:

quoted

On Tue, 2020-03-24 at 11:20 +0100, Bastien Nocera wrote:

quoted

On Wed, 2020-03-18 at 19:27 +0000, Filipe Laíns wrote:

quoted

As discussed in the mailing list:

quoted

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.

Why is it a problem that user-space communication fails? Note that
sending a signal without any way to fetch the state means that it's
always going to be racy.

It failing is not the problem. The problem is knowing when the device
is available again. Right now the only way to do that is to listen
for
events or periodically ping it.

We want to only export the HID++ hidraw node when the device is
available but that will take a while. We will have to test and sync
up
userspace. I also want to write tests for the driver before, to make
sure there are no regressions. We had a thread discussing this, IIRC
you were in CC.

If I need to remember some old thread to know what we're talking about,
then that means that the commit message is probably not good enough...

Should I put in the commit message what is planned next?

Please add some links to the relevant discussion on bug forums if
there's interesting data there too.

You can find the discussion in [1][2].

[1] https://www.spinics.net/lists/linux-input/thrd2.html#65615
[2] https://www.spinics.net/lists/linux-input/msg65615.html

quoted

quoted

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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 <redacted>

---

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-

quoted

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:

-- 
Filipe Laíns