Most Cardbus bridges supported by pccbb(4) fire a power-cycle
interrupt when the power state of a cardslot changes from 'off' to
'on'. TI bridges fire a power-cycle interrupt on both on->off and
off->on changes.
When pccbb_power() powered-down a cardslot, it did not wait around
for the power-cycle interrupt. When pccbb_power() powered-up a
cardslot, it did wait for the interrupt. If a pccbb_power(UP)
followed a pccbb_power(DOWN) very closely, pccbb_power() used to
interpret the power-cycle interrupt for the up->down transition as
"power-up complete," read the power-state bit and, finding that
power had NOT been activated, complain, "cbb0: power on failed?"
Then pccbb_power() exited before power-activation was complete,
falsely indicating that the power-activation *was* complete. After
that, a driver attach/enable routine would blithely configure a
card that was not fully powered-up. An operator who ran a command
such as 'ifconfig rtw0 down up' or 'ifconfig ath0 down up' would
read 'cbb0: power on failed?' in the system log, and their NIC
would misbehave.
This excerpt from a comment in the source should suffice to explain
how I fixed the bug,
/*
* Wait as long as 200ms for a power-cycle interrupt. If
* interrupts are enabled, but the socket has already
* changed to the desired status, keep waiting for the
* interrupt. "Consuming" the interrupt in this way keeps
* the interrupt from prematurely waking some subsequent
* pccbb_power call.
And this explains why this patch will work for Ricoh bridges that
do not fire an interrupt on the on->off transition:
* XXX Not every bridge interrupts on the ->OFF transition.
* XXX That's ok, we will time-out after 200ms.
*
* XXX The power cycle event will never happen when attaching
* XXX a 16-bit card. That's ok, we will time-out after
* XXX 200ms.
*/
M. Warner Losh and Charles M. Hannum provided valuable input on
this patch.
$NetBSD: README,v 1.3 1998/08/15 03:02:46 mycroft Exp $
This directory contains files which are used during PCI configuration
and PCI device drivers. Eventually, most of the device drivers and
some of the configuration support should become machine-independent
and be moved to a more general location.
The configuration support was implemented according to the `PCI Local
Bus Specification, Production Version, Revision 2.0' dated April 30,
1993. Section numbers referred to in the code may be specific to that
edition of the specification.
Some attempt has been made to insure that the code works on rogue
machines where the BIOS doesn't do its job, but in general I can't
guarantee that.
--
- Charles M. Hannum
NetBSD group
August 8, 1994
fa956bd2bd