benh@kernel.crashing.org said:
> actually, the device model defines a bus "type" structure rather than a
> "bus instance" structure (well, at least it did last I looked a couple
> of weeks ago). That's a problem I beleive here, as those functions are
> really a property of a given bus instance. One solution would
> eventually be to have the set of functions pointers in the generic
> struct device and by default be copied from parent to child.
Well, the bus in the generic device model is just a struct device as well.
The parisc implementation I'm working on stores this type of conversion
information in the platform_data field of the generic device (although the
function pointers that make use of it are global).
I did do an implementation which added a dma_accessors set of functions to the
struct device (and also struct bus_type), but I eventually concluded they had
to be so platform specific that there was no utility to exposing them.
> Consistency of memory (or simply, in some cases, accessibility of
> system memory by a given device) is really a property of the bus.
> Tweaking magic bits in dma_addr_t and testing them later is a hack.
> The proper implementation is to have the consistent_{alloc,free,map,unm
> ap,sync,...) functions be function pointers in the generic bus
> structure.
actually, in parisc, the implementation is simple. The type of memory is
determined globally per architecture (so it's not encoded in the dma_addr_t).
As Adam said. The preferred platform implementation for a machine that did
both (I believe this is the fabled parisc V class, which I've never seen)
would be to implement a consistent region so you could tell if dma_addr_t fell
in that region for whether it was consistent or not.
I fully recognise that dma_addr_t actually has to be freely convertable to the
physical address by simple casting, because that's the way the pci_ functions
use it.
James
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
This archive was generated by hypermail 2b29 : Sat Dec 07 2002 - 22:00:22 EST