From: Bastien Nocera <hadess@hadess.net>
To: "Filipe Laíns" <lains@archlinux.org>,
"Jiri Kosina" <jikos@kernel.org>,
"Benjamin Tissoires" <benjamin.tissoires@redhat.com>,
linux-input@vger.kernel.org, linux-kernel@vger.kernel.org,
"Peter Hutterer" <peter.hutterer@redhat.com>,
"Hans de Goede" <hdegoede@redhat.com>,
"Mario Limonciello" <superm1@gmail.com>,
"Richard Hughes" <hughsient@gmail.com>
Subject: Re: [PATCH v2] HID: logitech-dj: issue udev change event on device connection
Date: Tue, 24 Mar 2020 15:24:02 +0100 [thread overview]
Message-ID: <8d28db34b3075c524c7e5fec49c3f2e252d24552.camel@hadess.net> (raw)
In-Reply-To: <3c20624ea9d88f13d6f1a768735f08a4a8a59ea6.camel@archlinux.org>
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@archlinux.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:
prev parent reply other threads:[~2020-03-24 14:24 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-18 16:19 [PATCH] HID: logitech-dj: issue udev change event on device connection Filipe Laíns
2020-03-18 17:15 ` Mario Limonciello
2020-03-18 17:20 ` Hans de Goede
2020-03-19 2:23 ` Peter Hutterer
2020-03-21 0:05 ` Jiri Kosina
[not found] ` <CA+EcB1P0qW4hdWG1YAYkD6X8jL1OaXZn4Lfu7aCmGBqwOPrJyA@mail.gmail.com>
2020-03-21 0:29 ` Peter Hutterer
2020-03-18 19:23 ` Filipe Laíns
2020-03-18 19:27 ` [PATCH v2] " Filipe Laíns
2020-03-24 10:20 ` Bastien Nocera
2020-03-24 13:46 ` Filipe Laíns
2020-03-24 14:03 ` Bastien Nocera
2020-03-24 14:10 ` Filipe Laíns
2020-03-24 14:24 ` Bastien Nocera [this message]
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