On Tue, 2020-03-24 at 14:10 +0000, Filipe Laíns wrote: > On Tue, 2020-03-24 at 15:03 +0100, Bastien Nocera wrote: > > On Tue, 2020-03-24 at 13:46 +0000, Filipe Laíns wrote: > > > On Tue, 2020-03-24 at 11:20 +0100, Bastien Nocera wrote: > > > > On Wed, 2020-03-18 at 19:27 +0000, Filipe Laíns wrote: > > > > > 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. > > > > > > > > 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? You should put in everything that explains why this change is needed, and how user-space is supposed to use that information. Nobody should have to refer back to the mailing-list thread to find this out. > > 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 I was in CC: because "might be maintaining one of the affected userspace stacks", but I don't know what that stack might be for me. Is it for upower (which I only work on seldom and definitely don't maintain), or something else? > > > > > 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@xxxxxxxxxxxxx> > > > > > > > > > > --- > > > > > > > > > > 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:
