On Sun, 6 Apr 2014, vichy wrote:
> hi alan:
> >> Why you think it is a bug in hardware?
> >
> > The timeout error means that the kernel told the controller to turn off
> > the PORT_RESET bit, and 1000 us later the bit was still on. That's a
> > hardware bug.
> after checking my hardware I found if device is no connected and do
> the port reset,
> the reset bit always will be 1 (I purposely add port status check in
> set port reset case like below)
>
> Platform-ehci Platform-ehci.0: port 1 reset
> Platform-ehci Platform-ehci.0: in port reset sequence, GetStatus
> port:1 status 000100 0 ACK sig=se0 RESET
Yep. That's a hardware bug.
> from ehci spec, there did not mention what will HW to do if port reset
> happens on no connection.
> it only explain what controller needs to do when device is connected.
Nonsense. The EHCI spec says this (in Table 2-16, the description
for bit 8):
... Software writes a zero to this bit to terminate
the bus reset sequence...
... Note that when software writes a zero to this bit there
may be a delay before the bit status changes to a zero. The bit
status will not read as a zero until after the reset has
completed... A host controller must terminate the reset and
stabilize the state of the port within 2 milliseconds of
software transitioning this bit from a one to a zero.
Thus, the bit is supposed to change to 0 after no more than 2 ms,
whether a device is connected or not.
> if related reset bit will automatically cleared for a while when
> device is not connected.
> Why we still need to clear them in hub_port_finish_reset like below flow
> in hub_port_reset,
> /* Check for disconnect or reset */
> if (status == 0 || status == -ENOTCONN || status == -ENODEV) {
> hub_port_finish_reset(hub, port1, udev, &status);
> then in hub_port_finish_reset
> case -ENOTCONN:
> case -ENODEV:
> clear_port_feature(hub->hdev,
> port1, USB_PORT_FEAT_C_RESET);
That's a different bit. USB_PORT_FEAT_C_RESET isn't the same as
USB_PORT_FEAT_RESET.
> if (hub_is_superspeed(hub->hdev)) {
> clear_port_feature(hub->hdev, port1,
> USB_PORT_FEAT_C_BH_PORT_RESET);
> clear_port_feature(hub->hdev, port1,
> USB_PORT_FEAT_C_PORT_LINK_STATE);
> clear_port_feature(hub->hdev, port1,
> USB_PORT_FEAT_C_CONNECTION);
> }
Same goes for these bits.
Alan Stern
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