Message-ID: <667c2c8307e0e738ed54e34f6c83ea1df99c7528.camel@archlinux.org>
Subject: Re: I need advice with UPS connection. (ping)
From:   Filipe =?ISO-8859-1?Q?La=EDns?= <lains@archlinux.org>
To:     Alan Stern <stern@rowland.harvard.edu>,
        David Niklas <Hgntkwis@vfemail.net>,
        Jiri Kosina <jikos@kernel.org>,
        Benjamin Tissoires <benjamin.tissoires@redhat.com>
Cc:     linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org,
        linux-input@vger.kernel.org
In-Reply-To: <YZv55KMsuSYanfYp@rowland.harvard.edu>
References: <20201109220000.2ae98fa5@Phenom-II-x6.niklas.com>
         <20211114144842.72463ccc@Zen-II-x12.niklas.com>
         <20211114211435.GA87082@rowland.harvard.edu>
         <20211114220222.31755871@Zen-II-x12.niklas.com>
         <20211115160918.GB109771@rowland.harvard.edu>
         <20211117002359.03b36ec6@Zen-II-x12.niklas.com>
         <20211117170817.GD172151@rowland.harvard.edu>
         <20211119171915.6a8cac47@Zen-II-x12.niklas.com>
         <YZm03KTcWOwtMtCN@rowland.harvard.edu>
         <20211122112526.501c5f66@Zen-II-x12.niklas.com>
         <YZv55KMsuSYanfYp@rowland.harvard.edu>
Organization: Archlinux
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Date:   Mon, 22 Nov 2021 21:29:47 +0000
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On Mon, 2021-11-22 at 15:13 -0500, Alan Stern wrote:
> On Mon, Nov 22, 2021 at 11:25:26AM -0500, David Niklas wrote:
> > Ok, I first edited the kernel to return -ENOMEM like you suggested but
> > the UPS still disconnected. I then edited it again to re-add the 1060
> > byte request and the UPS still disconnected.
> >=20
> > I'm attaching the usbmon traces.
> > If you need any additional info I'll do my best to provide it.
>=20
> Holy cow!=C2=A0 I just realized what's going on.=C2=A0 And these little c=
hanges=20
> we've been messing around with have nothing to do with it.
>=20
> For the first time, I looked at the timestamps in the usbmon traces.=C2=
=A0 It=20
> turns out that the disconnects occur several seconds after the kernel=20
> retrieves the HID report descriptor from the device.=C2=A0 Under normal=
=20
> conditions we would expect to see report packets coming in from the=20
> device, starting just a fraction of a second after the descriptor is=20
> received.=C2=A0 But that isn't happening in the Linux traces, whereas it =
does=20
> happen in the Windows pcap log.
>=20
> I would guess that the UPS is programmed to disconnect itself=20
> electronically from the USB bus if it doesn't get any requests for=20
> reports within a couple of seconds.=C2=A0 That certainly would explain wh=
at=20
> you've been seeing.=C2=A0 I can't imagine why it would be programmed to=
=20
> behave this way, but companies have been known to do stranger things.
>=20
> As for why the kernel doesn't try to get the reports...=C2=A0 That's a li=
ttle=20
> harder to answer.=C2=A0 Maybe Jiri or Benjamin will know something about =
it.=C2=A0=20
>=20
> The UPS's vendor ID is 0d9f (POWERCOM) and the product ID is 0004.=C2=A0 =
Now,=20
> the drivers/hid/hid-quirks.c file contains a quirk entry for 0d9f:0002=
=20
> (product POWERCOM_UPS), which is probably an earlier model of the same=
=20
> device, or a very similar device.=C2=A0 This quirk entry is in the=20
> hid_ignore_list; it tells the HID core not to handle the device at all.
>=20
> I don't know why that quirk entry is present, and furthermore, it can't=
=20
> directly affect what is happening with your device because the product=
=20
> IDs are different.=C2=A0 Still, it is an indication that something strang=
e is=20
> going on behind the scenes.
>=20
> Perhaps there is no kernel driver for these UPS devices?=C2=A0 Perhaps th=
e=20
> intention is that some user program will handle all the communication=20
> when one of them is detected?=C2=A0 A quick search on Google turns up=20
> usbhid-ups, part of Network USB Tools (NUT) -- maybe you need to=20
> install that package in order to use the device.
>=20
> I don't know what the full story is.=C2=A0 With luck, Jiri or Benjamin ca=
n=20
> help more.
>=20
> Alan Stern

hid-generic should be able to handle these devices, but UPSes are much less
tested than normal input peripherals, so it's not that surprising that ther=
e may
be some unexpected weirdness. FWIW, I have two UPSes, one works OOTB and th=
e
other doesn't, I have been meaning to investigate the issue. However, David=
's
case seems to me like a hardware quirk, but that's just my guess.

Cheers,
Filipe La=C3=ADns

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