Re: [PATCH] Stop pci_set_dma_mask() from failing when RAM doesn't exceed the mask anyway

[David Woodhouse <dwmw2@infradead.org>]

On Sat, 2009-08-01 at 18:00 +1000, Benjamin Herrenschmidt wrote:
> On Sat, 2009-08-01 at 08:54 +0100, David Woodhouse wrote:
> > On Sat, 2009-08-01 at 08:25 +1000, Benjamin Herrenschmidt wrote:
> > > On Fri, 2009-07-31 at 20:41 +0100, David Woodhouse wrote:
> > > > On an iMac G5, the b43 driver is failing to initialise because trying to
> > > > set the dma mask to 30-bit fails. Even though there's only 512MiB of RAM
> > > > in the machine anyway:
> > > > 	https://bugzilla.redhat.com/show_bug.cgi?id=514787
> > > > 
> > > > We should probably let it succeed if the available RAM in the system
> > > > doesn't exceed the requested limit.
> > > > 
> > > > Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
> > > 
> > > Also, isn't our iommu code smart enough to clamp allocations to the DMA
> > > mask nowadays ? In that case, we could probably just force iommu on
> > > always...
> > 
> > We're not using the IOMMU on this box:
> > 
> > PowerMac motherboard: iMac G5
> > DART: table not allocated, using direct DMA
> 
> I know, I was suggesting we do :-)

I'm not sure. Losing 16MiB on a machine which only has 512MiB anyway
doesn't seem ideal, and we'll want to make the no-iommu code DTRT
_anyway_, surely?

So we might as well let the DART keep its existing logic (which is only
to bother if we have more than 1GiB of RAM; a limit chosen specifically
because of the Broadcom brokenness).

-- 
David Woodhouse                            Open Source Technology Centre
David.Woodhouse@intel.com                              Intel Corporation