How should I deal with a PCI resource not aligned to a page boundary?
ajax at nwnk.net
Wed Feb 17 12:27:07 PST 2010
On Wed, 2010-02-17 at 12:13 -0500, Alex Villacís Lasso wrote:
> After writing a somewhat functional xorg driver for the OAK Spitfire
> OTI64111 video card, I am trying to modify the driver to support the
> OTI64107 video card, which I have plugged in my test machine. The first
> strange thing that I notice about this card is that it reports a MMIO
> region that is not aligned to a page boundary (4096 bytes on this x86
> PC). Instead it reports an physical address like 0xffeff800, both
> through lspci and through libpciaccess within my driver code. If I try
> to map this resource, I get a page-aligned address, but trying to
> actually use the resource at this mapping has no effect in the card. To
> get around this, I have done the following: extract the lower bits of
> the resource with (resource & 0xfff), and use these bits as an offset
> within the mapping. I do get access to the MMIO by doing this, but it
> feels like an ugly hack. What is the official way of dealing with this
> situation? What measures should I take when compiling this for a
> different architecture, or a 64-bit machine?
I think that's the correct thing to do, the hardware's just being weird.
For arches with a different page size, build the mask with
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