> Date: Fri, 09 Mar 2001 13:14:03 -0800
> From: David Brownell <[EMAIL PROTECTED]>
>[...]
> It feels to me like you're being inconsistent here, objecting
> to a library API for some functionality (mapping) yet not for
> any of the other functionality (alignment, small size, poisoning
> and so
> I wonder if it may be feasible to allocate a bunch of contiguous
> pages. Then, whenever the hardware returns a bus address, subtract
> the remembered bus address of the zone start, add the offset to
> the virtual and voila.
Even if not you can hash by page number not low bits so the hash is
> > Given that some hardware must return the dma addresses, why
> > should it be a good thing to have an API that doesn't expose
> > the notion of a reverse mapping? At this level -- not the lower
> > level code touching hardware PTEs.
>
> Because its' _very_ expensive on certain machines.
David Brownell writes:
> Given that some hardware must return the dma addresses, why
> should it be a good thing to have an API that doesn't expose
> the notion of a reverse mapping? At this level -- not the lower
> level code touching hardware PTEs.
Because its' _very_ expensive on
> > > Do lots of drivers need the reverse mapping? It wasn't on my todo list
> > > yet.
> >
> > I am against any API which provides this. It can be extremely
> > expensive to do this on some architectures,
The implementation I posted needed no architecture-specific
knowledge. If cost is
> Drivers can keep track of this kind of information themselves,
> and that is what I tell every driver author to do who complains
> of a lack of a "bus_to_virt()" type thing, it's just lazy
> programming.
I'd agree. There are _good_ reasons for having reverse mappings especially on
certain
On Fri, Mar 09, 2001, David S. Miller <[EMAIL PROTECTED]> wrote:
> Manfred Spraul writes:
> > Do lots of drivers need the reverse mapping? It wasn't on my todo list
> > yet.
>
> I am against any API which provides this. It can be extremely
> expensive to do this on some architectures, and
On Fri, Mar 09, 2001, David S. Miller [EMAIL PROTECTED] wrote:
Manfred Spraul writes:
Do lots of drivers need the reverse mapping? It wasn't on my todo list
yet.
I am against any API which provides this. It can be extremely
expensive to do this on some architectures, and since the
Drivers can keep track of this kind of information themselves,
and that is what I tell every driver author to do who complains
of a lack of a "bus_to_virt()" type thing, it's just lazy
programming.
I'd agree. There are _good_ reasons for having reverse mappings especially on
certain
Do lots of drivers need the reverse mapping? It wasn't on my todo list
yet.
I am against any API which provides this. It can be extremely
expensive to do this on some architectures,
The implementation I posted needed no architecture-specific
knowledge. If cost is the issue,
David Brownell writes:
Given that some hardware must return the dma addresses, why
should it be a good thing to have an API that doesn't expose
the notion of a reverse mapping? At this level -- not the lower
level code touching hardware PTEs.
Because its' _very_ expensive on certain
Given that some hardware must return the dma addresses, why
should it be a good thing to have an API that doesn't expose
the notion of a reverse mapping? At this level -- not the lower
level code touching hardware PTEs.
Because its' _very_ expensive on certain machines. You have
I wonder if it may be feasible to allocate a bunch of contiguous
pages. Then, whenever the hardware returns a bus address, subtract
the remembered bus address of the zone start, add the offset to
the virtual and voila.
Even if not you can hash by page number not low bits so the hash is way
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