Subject: Re: [PATCH] powerpc/mpc85xx: match with the pci bus address used by u-boot for all p1_p2_rdb_pc boards

From: Scott Wood <[email-masked]>
Date: Thu, 30 May 2013 09:43:28 -0500

On 05/30/2013 09:21:19 AM, Kumar Gala wrote:
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> On May 28, 2013, at 5:45 PM, Scott Wood wrote:
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> > On 05/16/2013 01:29:45 AM, Kevin Hao wrote:
> >> All these boards use the same configuration file p1_p2_rdb_pc.h in
> >> u-boot. So they have the same pci bus address set by the u-boot.
> >> But in some of these boards the bus address set in dtb don't match
> >> the one used by u-boot. And this will trigger a kernel bug in 32bit
> >> kernel and cause the pci device malfunction. For example, on a
> >> p2020rdb-pc board the u-boot use the 0xa0000000 as both bus address
> >> and cpu address for one pci controller and then assign bus address
> >> such as 0xa00004000 to some pci device. But in the kernel, the dtb
> >> set the bus address to 0xe0000000 and the cpu address to =20
> 0xa0000000.
> >> The kernel assumes mistakenly the assigned bus address 0xa0004000
> >> in pci device is correct and keep it unchanged. This will =20
> definitely
> >> cause the pci device malfunction. I have made two patches to fix
> >> this in the pci subsystem.
> >> http://patchwork.ozlabs.org/patch/243702/
> >> http://patchwork.ozlabs.org/patch/243703/
> >> But I still think it makes sense to set these bus address to match
> >> with the u-boot. This issue can't be reproduced on 36bit kernel.
> >> But I also tweak the 36bit dtb for the above reason.
> >
> > IIRC the reason for using 0xe0000000 on all PCIe roots is to =20
> maximize the memory that is DMA-addressable without involving swiotlb.
> >
> > Maybe U-Boot should be fixed?
> >
> > -Scott
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> I feel that u-boot was the way it is to allow accessing each bus from =20
> the command line in u-boot w/o big changes for >32-bit addressing.
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> Linux was able to handle the PCI bus addresses all being the same.

It's a bit of a hack though, in that you're using the device tree to =20
indicate how you want the hardware programmed rather than to describe =20
the hardware or even what U-Boot's done to it, and in that you can't =20
arbitrarily change what U-Boot chose -- it only works because you're =20
picking an address that U-Boot used for one of the PCIe controllers and =20
thus U-Boot covered it with a LAW.

-Scott=