Re: I need advice with UPS connection. (ping)

David Niklas
2021-11-19T22:19:23Z

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On Wed, 17 Nov 2021 12:08:17 -0500
Alan Stern <stern@rowland.harvard.edu> wrote:
> On Wed, Nov 17, 2021 at 12:23:59AM -0500, David Niklas wrote:
> > On Mon, 15 Nov 2021 11:09:18 -0500
> > stern@rowland.harvard.edu wrote:
> > <snip>
> > > You can test the theory by patching the kernel, if you want. The
> > > code to change is in the source file drivers/hid/usbhid/hid-core.c,
> > > and the function in question is hid_set_idle() located around line
> > > 659 in the file. Just change the statement:
> > >
> > > return usb_control_msg(dev, usb_sndctrlpipe(dev, 0),
> > > HID_REQ_SET_IDLE, USB_TYPE_CLASS |
> > > USB_RECIP_INTERFACE, (idle << 8) | report, ifnum, NULL, 0,
> > > USB_CTRL_SET_TIMEOUT);
> > >
> > > to:
> > >
> > > return 0;
> > >
> > > to prevent the Set-Idle request from being sent. If the device
> > > still insists on disconnecting then we'll know that this wasn't the
> > > reason.
> >
> > Ok, so I changed out the line above with "__panic(2);" and now my PC
> > just reboots.... Teasing :D
> > That didn't seem to change anything. I'll attach another dump just in
> > case it reveals more.
>
> It doesn't. :-( The Set-Idle request does not appear to be related to
> the problem.
>
> > > Also, if you have another system (say, one running Windows) which
> > > the UPS does work properly with, you could try collecting the
> > > equivalent of a usbmon trace from that system for purposes of
> > > comparison. (On Windows, I believe you can use Wireshark to trace
> > > USB communications.)
> >
> > Limitations of SW:
> > Wireshark works if you have windows in a virtual environment, but I
> > don't actually own... I mean license, any windowz products. I'm a
> > straight Luser.
> > So borrowed a windowz machine and plugged in the UPS. I then used
> > USBPcap to capture the data after installing the drivers. It has 4
> > things it can't detect:
> >
> > Bus states (Suspended, Power ON, Power OFF, Reset, High Speed
> > Detection Handshake)
> > Packet ID (PID)
> > Split transactions (CSPLIT, SSPLIT)
> > Duration of bus state and time used to transfer packet over the wire
> > Transfer speed (Low Speed, Full Speed, High Speed)
> >
> > I'm 100% certain the last 2 we don't care about. IDK about the
> > others.
>
> I don't think they matter. In principle the time delays might be
> important, but I rather doubt it.
>
> > Notes:
> > Here's the product page of my UPS.
> > https://www.newegg.com/opti-ups-ts2250b/p/N82E16842107014
> > The main webpage for USBPcap is here:
> > https://desowin.org/usbpcap/index.html
> > I can also try and use SnoopyPro and busdog if the output is
> > undesirable. USBPcap spits out a pcap file which can be analyzed by
> > wireshark using dissectors -- somehow (I really should practice using
> > wireshark.)
>
> Wireshark on my system has no trouble reading your pcap file.

Misunderstanding then. I was thinking in terms of the USBPcap docs. I was
saying a dissector would need to be written. I'm glad it worked for you.
https://desowin.org/usbpcap/dissectors.html
"Writing USB class dissector"

> > Test and capture procedure:
> > When I installed the drivers it asked me where to look for the UPS. I
> > didn't tell it the USB port until after I started USBPcap and then
> > plugged in the UPS. Then the GUI opened up and I could see a lot of
> > cool controls like the battery power, loading, etc. The loading was
> > 132W and the battery was at 100%. Then I ran a self test (There's a
> > button in the GUI) and it worked fine. Then I unplugged the UPS and
> > it crashed. Then I plugged it back in. All --100%-- of this is in the
> > pcap file.
>
> I'm just concentrating on the first part, up to the point where the
> unwanted disconnects occurred with Linux. So far as I can see, there
> are only two significant differences between the usbmon and wireshark
> traces:
>
> The Windows system doesn't transfer any of the string
> descriptors during initial enumeration, whereas the Linux
> system does. While this might be relevant, I don't think it is.
>
> When the Windows system requests the HID report descriptor from
> the device, it asks for 1060 bytes of data. The Linux system
> asks for only 996 bytes. (Note: The descriptor is exactly
> 996 bytes long, and that's how much data the device sends in
> either case.)
>
> It's entirely possible that this second discrepancy is somehow causing
> the problem. You can test this guess by applying the following patch:
>
> --- usb-devel.orig/drivers/hid/usbhid/hid-core.c
> +++ usb-devel/drivers/hid/usbhid/hid-core.c
> @@ -667,13 +667,16 @@ static int hid_get_class_descriptor(stru
> unsigned char type, void *buf, int size)
> {
> int result, retries = 4;
> + int size2 = size;
>
> + if (size == 996)
> + size2 = 1060;
> memset(buf, 0, size);
>
> do {
> result = usb_control_msg(dev, usb_rcvctrlpipe(dev, 0),
> USB_REQ_GET_DESCRIPTOR,
> USB_RECIP_INTERFACE | USB_DIR_IN,
> - (type << 8), ifnum, buf, size,
> USB_CTRL_GET_TIMEOUT);
> + (type << 8), ifnum, buf, size2,
> USB_CTRL_GET_TIMEOUT); retries--;
> } while (result < size && retries);
> return result;
>
> This will cause the kernel to ask for 1060 bytes rather than 996.
> (It's also potentially dangerous, because it asks for 1060 bytes to be
> stored into a 996-byte buffer; if the device sends more data than
> expected then the excess will be written beyond the end of the buffer.)
>
> Please send a usbmon trace showing what happens with this patch
> applied. And you might as well put the Set-Idle request back in,
> because now we know Windows does send that request.
>
<snip>

It still disconnects. I've attached the usbmon output.

Thanks,
David

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