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Re: [PATCH 2/3] i386: add io_map_cached
From: |
Justus Winter |
Subject: |
Re: [PATCH 2/3] i386: add io_map_cached |
Date: |
Tue, 01 Jul 2014 11:22:38 +0200 |
User-agent: |
alot/0.3.4 |
Quoting Samuel Thibault (2014-05-23 01:28:30)
> Justus Winter, le Thu 15 May 2014 12:32:41 +0200, a écrit :
> > Quoting Samuel Thibault (2014-05-15 02:13:13)
> > > Justus Winter, le Fri 02 May 2014 21:33:01 +0200, a écrit :
> > > > io_map_cached is like io_map, but reuses the old mapping if it is
> > > > applicable.
> > >
> > > But AIUI, if it is not applicable, it does not unmap the previous
> > > mapping, so we lose virtual memory.
> > >
> > > A really transparent io_map_cached seems not really feasible, since you
> > > never know what the caller will do with the pointer.
> >
> > Right, I did this b/c I didn't know how to do this properly.
>
> > accessing this physical address with phystokv() fails b/c it is
> > outside the mapped range
>
> Ok. I'd say then to just use io_map once for accessing that (AIUI one
> knows the needed size), and then free the mapped memory region after
> that with kmem_free.
I don't believe one knows the size in advance. Every acpi table has a
header with explicit size information. From a quick search through
this internet thing it appears that Linux at some point just mapped a
page or so, but that turned out to be problematic.
Justus
- Re: [PATCH 2/3] i386: add io_map_cached,
Justus Winter <=