From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Albert Cahalan <acahalan@gmail.com>
Cc: linuxppc-dev@lists.ozlabs.org
Subject: Re: use of BAT before taking over the MMU
Date: Tue, 05 Oct 2010 19:11:03 +1100 [thread overview]
Message-ID: <1286266263.2463.337.camel@pasglop> (raw)
In-Reply-To: <AANLkTikt9e5s3UUn1+k=NY7UhqosM5qkgdih=UD+Hd+L@mail.gmail.com>
On Mon, 2010-10-04 at 12:06 -0400, Albert Cahalan wrote:
> On Mon, Oct 4, 2010 at 12:25 AM, Segher Boessenkool
> <segher@kernel.crashing.org> wrote:
>
> > The PowerPC OF binding requires the firmware to save and restore
> > the BATs on entry to / exit from the firmware.
>
> This sucks, because using the BAT is **much** easier for
> the firmware. In my case, it also means I don't need to worry
> about Linux stomping on anything -- I have nothing in RAM.
What FW are we talking about here anyways ? As I said, Linux isn't
supposed to take any fault from the moment it starts setting up BATs to
the moment it takes over exceptions and can handle faults all by itself.
> (this is an emulator, but I don't want to cheat too much
> because adding special cases affects performance)
>
> Page tables would need to go in RAM. If Linux wants to
> use that memory...? It seems that Linux does tend to ask;
> will it panic if I refuse? Are there addresses Linux won't
> ever ask for?
>
> It also looks like I could just start up Linux w/o the MMU on.
> I'm just making 1:1 mappings anyway.
Cheers,
Ben.
next prev parent reply other threads:[~2010-10-05 8:11 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-10-02 18:32 use of BAT before taking over the MMU Albert Cahalan
2010-10-04 4:25 ` Segher Boessenkool
2010-10-04 16:06 ` Albert Cahalan
2010-10-05 7:54 ` Segher Boessenkool
2010-10-05 8:11 ` Benjamin Herrenschmidt [this message]
2010-10-05 8:10 ` Benjamin Herrenschmidt
2010-10-05 12:05 ` Albert Cahalan
2010-10-05 12:28 ` Benjamin Herrenschmidt
2010-10-05 15:31 ` Segher Boessenkool
2010-10-07 2:05 ` Albert Cahalan
2010-10-07 8:00 ` Benjamin Herrenschmidt
2010-10-05 15:22 ` Segher Boessenkool
2010-10-05 8:09 ` Benjamin Herrenschmidt
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