Re: [PATCH for review] [69/145] x86_64: Disable DAC on VIA PCI bridges

Muli Ben-Yehuda
2006-08-11T19:13:14Z

On Fri, Aug 11, 2006 at 08:51:53AM +0200, Andi Kleen wrote:

> I've haven't decided yet. I put it out for review for now at least.
>
> I got various reports of the VIA bridges having trouble with DAC over the
> years, but usually when I asked for confirmation the reporters disappeared.
> I finally did the patch now because with cheap 2GB DIMMs VIA systems
> with 4GB (which gives some memory over 4GB) are becomming more common.
>
> But again the last reporters disappeared this time.
>
> I will probably not sent it off before final confirmation again.

Ok. I'll give it and the rest of the patches a spin on my systems with
and without Calgary on Sunday.

> > > int dma_supported(struct device *dev, u64 mask)
> > > {
> > > if (dma_ops->dma_supported)
> > > return dma_ops->dma_supported(dev, mask);
> >
> > I just checked, no ops has a dma_supported method... should we remove
> > it?
>
> The if()? Possible.

the .dma_supported member of dma_ops. If no one is using it, I don't
see a point in keeping it there - we can always reintroduce it when an
IOMMU implementation that needs it comes along.

> > > + if (!strncmp(p, "nodac", 5))
> > > + allow_dac = -1;
> >
> > Why <0? we usually set 1 for enabled and 0 for disabled.
>
> For hardware workarounds it is usually best to have three values:
>
> - Force disabled
> - Default based on black/white list
> The black/white list is not active when != 0
> - Force enabled
>
> I tend to use -1/0/1 for this.

I understand, makes sense. Thanks.

Cheers,
Muli