On 5/18/06, Guennadi Liakhovetski <[EMAIL PROTECTED]> wrote:
Hi all,
I've experimented a bit with the hub-power switching program from NIIBE
Yutaka and I've got a couple of questions to my observations.
On Sat, 14 Jan 2006, NIIBE Yutaka wrote:
> Vlado Handziski wrote:
>> http://thread.gmane.org/gmane.linux.usb.devel/36739
>>
>>
>> at the end I have posted a python wrapper over libusb for controlling the
>> hub port power. The issue with the "self-healing" in the kernel is still
>> there. We are currently patching the kernel to disable the automatic
>> re-powering.
First short question - what is this about? I haven't seen any such
attempts under 2.6.16/17-rc3? Have they been in the meantime fixed?
The problem occurs when there is a hub downstream from the power
controlled port. For example, in the following topology with 2 hubs:
H_C->HUB1->HUB2->USB_DEVICE
if the port on HUB1 to which HUB2 is attached (the upstream port of
HUB2) is switched off, the kernel driver detects -EPROTO errors, and
after 10 retries re-powers the whole chain, ultimately re-powering the
managed port and the downstream devices. For our application, we have
modified the driver to simply ignore the -EPROTO events.
--- linux-2.6.16/drivers/usb/core/hub.c.old 2006-05-09
10:58:15.000000000 +0200
+++ linux-2.6.16/drivers/usb/core/hub.c 2006-05-09 10:57:42.000000000 +0200
@@ -302,6 +302,7 @@ static void hub_irq(struct urb *urb, str
case -ENOENT: /* synchronous unlink */
case -ECONNRESET: /* async unlink */
case -ESHUTDOWN: /* hardware going away */
+ case -EPROTO: /* port power off */
return;
default: /* presumably an error */
This is quick and dirty and can cause state consistency problems since
the driver is not aware about the external power control commands.
Having said that, we would be happy to help in designing/implementing
a "proper" solution that would keep the internal state machine of the
driver sane while allowing user-space port power control.
Vlado
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