Hello,
I have a somewhat strange request: how to break Linux USB support and disable some
validation.
Recently I have become a "lucky" owner of the badly designed hardware (ZWO 120MM astronomy
camera to be specific) and stumbled upon classic issue: hardware was designed not
according to specifications, but to work on Windows. From what I was able to dig on ZWO
forums , camera uses bulk transfer mode, but uses incorrect packet size of 1024 bytes.
Windows ignores that, Linux - does not. As a result camera does not work in Linux.
There are repeated messages in kern.log "usb 1-1: reset high-speed USB device number 8
using ehci_hcd" and "usb usb1-port1: disabled by hub (EMI?), re-enabling..." each time I
attempted to use camera.
In ZWO forums there was a suggestion to revert USB packet validation by applying a "break"
to Linux kernel. With some changes to line locations I have applied the patch below and
camera started to work on a desktop with USB 2.0 host. However this patch does not help if
camera is attached to a laptop with USB 3.0 host. Each time I try to use camera, I see
similar error messages, but now originating from xhci_hcd.
Question: can anyone point what lines should be commented out to ignore packet sizes for
USB 2.0 device, when attached to USB 3.0 host?
As I am not much of C programmer I have not been able to locate those myself and did not
want to play "whack a mole" by commenting out some random line, wait ~1 hour to compile
kernel and see that nothing good happens.
-------------------- CUT LINE -------------------
--- config.c.ORIG 2018-03-14 19:48:11.000000000 +0200
+++ config.c 2018-04-16 19:45:24.538599024 +0300
@@ -374,10 +374,12 @@
j = maxpacket_maxes[usb_endpoint_type(&endpoint->desc)];
if (maxp > j) {
- dev_warn(ddev, "config %d interface %d altsetting %d endpoint 0x%X has invalid
maxpacket %d, setting to %d\n",
+ dev_warn(ddev, "config %d interface %d altsetting %d endpoint 0x%X has invalid
maxpacket %d, setting to %d (IGNORED!)\n",
cfgno, inum, asnum, d->bEndpointAddress, maxp, j);
+ #if 0
maxp = j;
endpoint->desc.wMaxPacketSize = cpu_to_le16(i | maxp);
-------------------- CUT LINE -------------------
PS I know that not the ideal way to solve the problem, but booting customized kernel just
for the imaging sessions for me seems to be a good trade off.
Thank you
--
Informatikas - diagnozė, o ne specialybė
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