Johannes,
Did you look over the patch yet?
Gosh, even USB 2.0 still only allows 127 devices (per
bus/controller). Why the 255?
~Randy
-----Original Message-----
From: Johannes Erdfelt [mailto:[EMAIL PROTECTED]]
Sent: Saturday, June 17, 2000 9:05 AM
To: Brad Hards
Cc: Dunlap, Randy; '[EMAIL PROTECTED]'
Subject: Re: [linux-usb] Monitor with embedded hub
On Sat, Jun 17, 2000, Brad Hards <[EMAIL PROTECTED]> wrote:
> Johannes Erdfelt wrote:
> >
> > On Fri, Jun 16, 2000, Dunlap, Randy <[EMAIL PROTECTED]> wrote:
> > > I got a CTX monitor/hub this week and spent today
> > > looking into this problem. The problem is that
> > > the hub doesn't like to return a partial descriptor
> > > in usb_hub_configure() [2-byte "header" is requested].
> > >
> > > I have made 2 workarounds for this and either one
> > > of them works, but I'd like your opinion on them,
> > > then one of us can make a patch to hub.c.
> > >
> > > A. Do the normal 2-byte header request, then handle
> > > this error case (something like):
> > >
> > > if (ret == -EPIPE &&
> > > (vendor == CTX) && (product == 0x9999)) {
> > > /* simulate good desc & clear the stall */
> > > bLength = 2;
> > > bDescType = USB_DT_HUB;
> > > if (usb_clear_halt(dev, usbrcvctrlpipe(dev, 0)))
> > > return -1;
> > > }
> > > ...
> > >
> > > . More direct, less intrusive to the current code.
> > >
> > > or:
> > >
> > > B. Don't do a 2-byte header request; do a header request
> > > of 13 bytes [or maybe even larger, but 13 bytes is enough
> > > for a 16-port hub]. This requires only one get_hub_desc()
> > > call instead of 2. Instead of the 2nd call, just
> > > memcpy (bitmap, buffer, header->bLength).
> > > [Think we'll ever need to support more than 16 ports on
> > > a hub?]
> > >
> > > . More general solution [unless we find some hub that doesn't
> > > like descriptor requests that are _larger_ than actual].
> > > . Calls get_hub_desc() one time instead of 2 times.
> > >
> > > I tested both methods with a keyboard and floppy drive
> > > on UHCI (both HCDs) and OHCI.
> > >
> > > Which method do you prefer? Do you want to make a hub.c
> > > patch for this or have me do it? I'll be glad to send
> > > my patches to you, of course.
> >
> > I like option B, but why don't we just request 39 bytes?
> >
> > That's 7 bytes for the base hub descriptor, 16 bytes for DeviceRemovable
> > (127 ports) and 16 bytes for PortPwrCtrlMask (127 ports).
>
> Any reason why you chose 127?
> Table 11-8 of USB Spec Rev 1.1 says "maximum of 255 ports". So that
> should be 7+32+32 or about 71 bytes requested.
Because you can only enumerate 127 devices on the bus. I wonder why that
says
255. I guess we could set it to 71 without any worries as well.
JE
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