From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Roland Dreier <rdreier@cisco.com>
Cc: linuxppc-dev@ozlabs.org, Joachim Fenkes <fenkes@de.ibm.com>,
Paul Mackerras <paulus@samba.org>
Subject: Re: [PATCH] Allow drivers to map individual 4k pages to userspace
Date: Wed, 04 Apr 2007 13:23:45 +1000 [thread overview]
Message-ID: <1175657025.30879.45.camel@localhost.localdomain> (raw)
In-Reply-To: <adar6r0dg0q.fsf@cisco.com>
> The problem with this approach is that remap_4k_pfn is
> powerpc-specific, right? For example, I don't believe that an ia64
> kernel running with 16K pages could implement this. Which means that
> any driver that calls remap_4k_pfn is now powerpc-specific (or has an
> #ifdef to work around this).
>
> In fact my impression was that the powerpc MMU is not part of the
> architecture, in the sense that a new implementation could come along
> that supported 64K pages without the ability to do this 4K aliasing
> trick. Which would make multiplatform kernels very painful, since
> remap_4k_pfn might work for some platforms the kernel could boot on.
> Or is this not a problem?
It's somewhat architected. I doubt there will ever be a processor that
can have an eHCA and doesn't support that trick. The thing is, eHCA is
platform specific, so the remap_4k_pfn would have to be called by driver
specific code, but that's not a problem since that driver will only ever
be used on those platforms that support that call.
Ben.
next prev parent reply other threads:[~2007-04-04 3:24 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-04-03 11:24 [PATCH] Allow drivers to map individual 4k pages to userspace Paul Mackerras
2007-04-04 2:34 ` Roland Dreier
2007-04-04 3:23 ` Benjamin Herrenschmidt [this message]
2007-04-04 4:07 ` Roland Dreier
2007-04-04 4:43 ` Benjamin Herrenschmidt
2007-04-04 5:14 ` Paul Mackerras
2007-04-04 4:41 ` Paul Mackerras
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