On Thu, Jan 10, 2013 at 11:20:07AM -0700, Jason Gunthorpe wrote: > On Thu, Jan 10, 2013 at 11:25:44AM +0100, Thierry Reding wrote: > > On Thu, Jan 10, 2013 at 09:17:19AM +0000, Arnd Bergmann wrote: > > > On Thursday 10 January 2013, Thierry Reding wrote: > > > > On Wed, Jan 09, 2013 at 04:17:58PM -0700, Jason Gunthorpe wrote: > > > > > On Wed, Jan 09, 2013 at 04:12:31PM -0700, Stephen Warren wrote: > > > > > You could decrease the size of the mapping to only span the bus > > > > > numbers that are configured for use via DT. > > > > > > > > That won't work, unfortunately. The mapping is such that the bus number > > > > is not encoded in the uppermost bits, the extended register number is. > > > > So the only thing that we could do is decrease the size of the extended > > > > register space for *all* devices. > > > > > > But you could still a method to map 16 separate areas per bus, each 65536 > > > bytes long, which results in 1MB per bus. That is probably ok, since > > > very few systems have more than a handful of buses in practice. > > > > > > In theory, doing static mappings on a per-page base would let you > > > do 16 devices at a time, but it's probably worth doing at this fine > > > granularity. > > > > I don't understand how this would help. The encoding is like this: > > > > [27:24] extended register number > > [23:16] bus number > > [15:11] device number > > [10: 8] function number > > [ 7: 0] register number > > > > So it doesn't matter whether I use separate areas per bus or not. As > > soon as the whole extended configuration space needs to be accessed a > > whopping 28 bits (256 MiB) are required. > > You'd piece a mapping together, each bus requires 16 64k mappings, a > simple 2d array of busnr*16 of pointers would do the trick. A more > clever solution would be to allocate contiguous virtual memory and > split that up.. Oh, I see. I'm not very familiar with the internals of remapping, so I'll need to do some more reading. Thanks for the hints. > > > Actually, AER probably needs this, and I believe some broken devices > > > need to mask interrupts using the PCI command word in the config space, > > > it it can happen. > > > > Ugh... that would kill any such dynamic mapping approach. Perhaps if we > > could mark a device as requiring a static mapping we could pin that > > cache entry. But that doesn't sound very encouraging. > > AER applies to pretty much every PCI-E device these days. So given there's no way around a segmented static mapping as you suggested, right? Thierry
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