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Re: [Qemu-devel] [PATCH 0/2] [RFC] 64-bit io paths
From: |
Blue Swirl |
Subject: |
Re: [Qemu-devel] [PATCH 0/2] [RFC] 64-bit io paths |
Date: |
Thu, 22 Apr 2010 23:01:43 +0300 |
On 4/22/10, Richard Henderson <address@hidden> wrote:
> On 04/22/2010 12:38 PM, Blue Swirl wrote:
> > Subpages are used when there are several devices on the same page.
> > It's needed for at least Sparc32.
>
>
> That's fine.
>
>
> > Subwidth (with NULL) is used mainly to indicate that the device does
> > not accept accesses in some access widths. Sparc32 and Sparc64 need
> > this (or some other way to signal bus errors for bad access widths).
>
>
> This is also fine. Although by using NULL all you'd get is a qemu
> null pointer dereference; I suppose this might get caught and
> translated to an cpu exception, but I think it would be preferable
> long-term to be more explicit about this and fill in the entries
> with a function that would explicitly raise the exception.
Perhaps also the bus layer could do something here.
> What this *does* confirm for me is that we don't need to support
> multiple devices at the same address, differentiated by the size
> of the reference. Which is something that the current subpage
> implementation actually supports.
Yes, I also agree it's a bit overkill.
> I'll submit a patch to clean this up.
>
>
> > In fact, many system devices on Sparc64 should only accept 64 bit
> > accesses, but currently we can't enforce this.
>
>
> Cool. This is something that should be fixed by the end result
> of the driver interface re-design that pbrook and I have been
> discussing on IRC.
Interesting. Could you make a summary of the design for the benefit of the list?
- [Qemu-devel] [PATCH 0/2] [RFC] 64-bit io paths, Richard Henderson, 2010/04/20
- [Qemu-devel] [PATCH 2/2] io: Add readq/writeq hooks and use them., Richard Henderson, 2010/04/20
- [Qemu-devel] [PATCH 1/2] io: Add CPUIOMemoryOps and use it., Richard Henderson, 2010/04/20
- Re: [Qemu-devel] [PATCH 0/2] [RFC] 64-bit io paths, Blue Swirl, 2010/04/22
- [Qemu-devel] [PATCH] Remove IO_MEM_SUBWIDTH., Richard Henderson, 2010/04/22
- [Qemu-devel] Re: [PATCH] Remove IO_MEM_SUBWIDTH., Blue Swirl, 2010/04/25
- Re: [Qemu-devel] Re: [PATCH] Remove IO_MEM_SUBWIDTH., Artyom Tarasenko, 2010/04/26
- Re: [Qemu-devel] Re: [PATCH] Remove IO_MEM_SUBWIDTH., Richard Henderson, 2010/04/27
- Re: [Qemu-devel] Re: [PATCH] Remove IO_MEM_SUBWIDTH., Artyom Tarasenko, 2010/04/28