running configuration cycle across the secondary side of a non transparent(21554) bridge

Joe Green jgreen at
Tue Aug 14 02:28:10 EST 2001

bhupinder sahran wrote:
> i am trying to run configuration cycle across the
> secondary of 21554 bridge, from my MPC8240 on which
> linux is running.
> i am not able to write anything into the downstrean
> configuration register which is at offset 0x90 from
> the primary interface.
> i have enabled the downstream configuration control &
> status register also.
> i have tried to write through CSR I/O BAR also.
> but could not write.
> can anybody tell me what could be the reason.

The first thing to check is whether the primary access lockout has been
disabled.  The chip can come up in a mode where accesses via the
primary interface are rejected (generate PCI bus retries).  This can
only be cleared from the secondary interface.  You can strap the chip
or configure the serial ROM to disable this on startup.

Joe Green <jgreen at>
MontaVista Software, Inc.

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