On Fri, Feb 14, 2014 at 10:36:20AM +0800, FengHua wrote:
-Original Messages-
From: Wolfgang Denk w...@denx.de
Sent Time: 2014-02-14 00:30:24 (Friday)
To: feng...@phytium.com.cn
Cc: u-boot@lists.denx.de, tr...@ti.com, albert.u.b...@aribaud.net
Subject: Re: [PATCH][RFC v2] add pci 64 bit prefechable mem support
Dear feng...@phytium.com.cn,
In message 1392282108-56485-1-git-send-email-feng...@phytium.com.cn you
wrote:
From: David Feng feng...@phytium.com.cn
u-boot did not program the upper 32 bits of prefetchable base and limit
in pci bridge config space. I think it's needed when 64 bit address space
is used.
You write I think it's needed - is it or not?
Do you have a specific test case that fails without your patch, and
works with it?
Best regards,
Wolfgang Denk.
There's no test case now (maybe a few days later I could make a test).
PCI-to-PCI Bridge Architecture Specification require that the upper 32 bit
of prefetchable space
must be initialized by configuration software. But usually the default value
is zero already.
A board using 64 bit pci prefetchable memory space and a pci device with 64
bit prefetchable space
are needed. I think u-boot did not encounter this situation before.
There's two things happening here.
1) You are adding support to explicitly program the upper32 prefetch
limit/base to zero (in the 64-bit prefetch memory 4GB case) which is
a completely theoretical fix. I can more or less confirm that this
doesn't cause a problem in practice for prefetch memory 4GB. When I
wrote the original code in-kernel, I had noticed this on the 21154
bridges and others when I was trying out WIP prefetch support (which
I never finished to upstream because we let the kernel subsystem fix
up prefetch later). If we look at the history of the prefetch support
added to the U-Boot version of pci_auto.c it's also proven on real h/w
that this is only a theoretical fix. To be fair, it is best to be safe,
but as Wolfgang points out it appears you are fixing something that's
not practically broken
2) 64-bit prefetch support for prefetch memory 4GB. It's up to the
maintainers, but given that this is untested code, I don't see a good
reason to merge it. I have reviewed it and the implementation looks
correct to me per spec. However, I believe that you should resubmit this
patch along with support for a platform that actually makes use of it as
you describe above. At that time, it would be appropriate to fix the
possible latent bug (for a not-yet-known p2p bridge that doesn't default
upper32 limit/base to 0) in the 4GB case just as part of handling the
4GB case.
-Matt
___
U-Boot mailing list
U-Boot@lists.denx.de
http://lists.denx.de/mailman/listinfo/u-boot
