On Mon, 23 Apr 2018, Elvinas wrote:
> 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.
The patch you wrote isn't ideal; the one below is better. In fact, the
code should be like this already. It was an oversight.
> 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 far as I know, there is no way to do this. USB-3 xHCI host
controllers validate maxpacket sizes in the hardware, not in software,
and there isn't any way to change the hardware's behavior. But I am
not an expert on xHCI.
Does the camera work when attached to a USB-3 host controller on a
computer running Windows or Mac OS X?
> 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
Alan Stern
Index: usb-4.x/drivers/usb/core/config.c
===================================================================
--- usb-4.x.orig/drivers/usb/core/config.c
+++ usb-4.x/drivers/usb/core/config.c
@@ -191,7 +191,9 @@ static const unsigned short full_speed_m
static const unsigned short high_speed_maxpacket_maxes[4] = {
[USB_ENDPOINT_XFER_CONTROL] = 64,
[USB_ENDPOINT_XFER_ISOC] = 1024,
- [USB_ENDPOINT_XFER_BULK] = 512,
+
+ /* Bulk should be 512, but some devices use 1024: we warn below */
+ [USB_ENDPOINT_XFER_BULK] = 1024,
[USB_ENDPOINT_XFER_INT] = 1024,
};
static const unsigned short super_speed_maxpacket_maxes[4] = {
--
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