Re: [PATCH v2] HID: logitech-dj: issue udev change event on device connection
From: Bastien Nocera <hadess@hadess.net>
Date: 2020-03-24 10:20:28
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On Wed, 2020-03-18 at 19:27 +0000, Filipe Laíns wrote:
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.
quoted hunk ↗ jump to hunk
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: