linux-kernel - Re: Pegasos OHCI bug (was Re: PROBLEM: memory corrupting bug,

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Date:	Thu, 28 Oct 2010 01:33:52 +0200 (CEST)
From:	"Segher Boessenkool" <segher@...nel.crashing.org>
To:	pacman@...h.dhis.org
Cc:	"Segher Boessenkool" <segher@...nel.crashing.org>,
	"Olaf Hering" <olaf@...fle.de>, linuxppc-dev@...ts.ozlabs.org,
	linux-kernel@...r.kernel.org
Subject: Re: Pegasos OHCI bug (was Re: PROBLEM: memory corrupting bug,

>> 1) Figure out what exactly is going on;
>
> I thought we were past that.

We are not.

> The startup sequence leaves the device in a
> bad
> state (writing 1000 times per second to memory that the kernel believes is
> not in use), so it needs to be given a reset command before the kernel
> tries
> to use that memory.

The question now is what causes the firmware to do that, and then
what is the best way to stop it from doing that.

>> > The big question that I'm still stumbling over is how to access the
>> device
>> > registers. The "reg" property looks like this:
>>
>> You should look at "assigned-addresses", not "reg".  Well,
>> you first need to look at "reg" to figure out what entry
>> in "assigned-addresses" to use.

Ignore this part, I was confused.

> The properties look like this:
>
> /pci@...00000/usb@...ssigned-addresses
>  02002810 00000000 80000000 00000000 00001000

Lovely, incorrect data (it should start with 82002810, i.e.,
not relocatable -- it is already an assigned address!).

This means: 32-bit MMIO address space for bus 0 dev 5 fn 0,
first BAR; assigned to address 80000000; size is 1000.

You could try a boot script like this:

dev /pci
0 ffff04 DO 0 i config-w! -100 +LOOP
device-end

which should disable all PCI devices on all busses, on that
PCI host bus (it disables every device behind pci-pci bridges
separately, as long as every such bridge has a higher secondary
bus number than primary bus number; if you only want to disable
everything on the root bus (which should be sufficient), use
ff04 instead of ffff04).

Segher

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