Re: [Qemu-devel] [PATCH] usb-redir: Allow to attach USB 2.0 devices to 1.1 host controller

[Jan Kiszka <jan.kiszka@web.de>]

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On 2012-09-17 11:08, Hans de Goede wrote:
> Hi,
> 
> On 09/15/2012 06:27 PM, Jan Kiszka wrote:
>> From: Jan Kiszka <jan.kiszka@siemens.com>
>>
>> This follows the logic of host-linux: If a 2.0 device has no ISO
>> endpoint and no interrupt endpoint with a packet size > 64, we can
>> attach it also to an 1.1 host controller. In case the redir server does
>> not report endpoint sizes, play safe and remove the 1.1 compatibility as
>> well.
>>
>> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
> 
> Interesting thanks for the patch. I like the approach you took (simple
> code),
> but unfortunately it won't work, if you look at usbredir_device_connect(),
> where you do the dev->dev.speedmask |= USB_SPEED_MASK_FULL, it also
> actually attaches the device to the controller, from which point on the
> guest will see the device.
> 
> What happens on the wire is that the usbredir-host sends (in order):
> -ep_info + interface_info
> -device_connect message
> 
> So your clearing of the speed-mask will never trigger, unless ep-info
> gets repeated later (which it does under certain circumstances).

Hmm, what a pity...

> 
> I suggest instead changing the code to set a "fullspeed_compatible" flag
> in struct USBRedirDevice from usbredir_device_disconnect(), clear that
> flag from usbredir_ep_info and use it to add to the mask in
> usbredir_device_connect().

OK.

> 
> ###
> 
> Another issue is what happens if a device "grows" incompatible endpoints
> after being attached, ie a webcam could have no isoc endpoints in alt
> setting 0, and then grow an isoc endpoint on a set_interface. So we
> would need a check for a device becoming not fullspeed compat while
> being attached at fullspeed in usbredir_ep_info(), and then call
> usbredir_reject_device() when this happens.

...and this patch started so simple. OK.

> 
> Although not pretty I'm ok with this, since I actually want to add
> similar code to allow usb-3 (superspeed) devices like a usb-3 usb-stick
> to work with ehci or uhci controllers :)

Great, that would have been my next question, but I don't have hardware
for that around yet.

BTW, I'm facing several incompatibilities with passed-through CDC/ACM
devices (e.g. a Galaxy S2), independent of my patch. Both host-linux and
redir doesn't allow to use them properly but show different symptoms.
Need to analyze and report once time permits.

Jan



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