Re: [PATCH] powerpc: add Book E support to 64-bit hibernation

[Scott Wood <scottwood@freescale.com>]

On 03/19/2013 03:55:34 PM, Johannes Berg wrote:
> On Mon, 2013-03-18 at 17:12 -0500, Scott Wood wrote:
>=20
> > Could you elaborate on why book3s flushes the way it does?  What's
> > special about the first 32 MiB?  If it's to cover kernel code, why
> > would that be changing from what's already there?
>=20
> I was going to say I have no idea, but looking at it again ... this is
> in the *resume* code, not the suspend code as I'd assumed, and on =20
> resume
> I guess I felt it was safer to not assume it didn't change, since it
> could be a slightly different kernel that loaded and restored the
> hibernation image?

Wouldn't that be doomed for other reasons?

I wonder about kernel modules, though flushing 32 MiB wouldn't be =20
adequate there.

> It should be the same one, so I guess it should be
> exactly the same code, but I guess I wanted to make sure there wasn't
> anything weird there. As for why it'd be 32 MiB? No idea. Although =20
> that
> really ought to flush all your possible caches anyway, I guess.

It's not a displacement flush (i.e. you don't do a separate load pass =20
first) -- it just flushes lines if they happen to be present, and =20
leaves alone anything outside that range.  Given that you just finished =20
copying a bunch of data, most likely what's in the cache is the last =20
bit of data you copied.

-Scott=