linux-kernel - Re: [openib-general] [PATCH 2.6.19 2/4] ehca: hcp_phyp.c: correct page mapping in 64k page mode

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Message-ID: <OF75FFAC00.E43450CA-ONC1257222.002A402A-C1257222.002AB9BD@de.ibm.com>
Date:	Fri, 10 Nov 2006 08:49:48 +0100
From:	Christoph Raisch <RAISCH@...ibm.com>
To:	"Roland Dreier" <rdreier@...co.com>
Cc:	linux-kernel@...r.kernel.org, linuxppc-dev@...abs.org,
	openib-general@...nib.org, openib-general-bounces@...nib.org,
	"Paul Mackerras" <paulus@...ba.org>
Subject: Re: [openib-general] [PATCH 2.6.19 2/4] ehca: hcp_phyp.c: correct page
 mapping in 64k page mode


> Umm, so is this patch really needed?  Where did the patch come from --
> is it needed to fix something actually seen, or was it written just
> based on some theoretical understanding?
>
> I'm confused...
>
>  - R.
The patch is needed. We've seen it on the real system. We did fix it on the
real system.
...and it conforms to theory... although theory is a bit confusing here.

let me try to summarize:
ioremap checks for 64k boundary (actually page boundary)
nopage does H_ENTER in 4k granularity if it's configured like that for a
certain type of POWER processor.

so you have to adjust the ioremap to page boundary, and THEN access at the
offset within the 64k.

Took quite a while until we understood that code path.... ;-)

Christoph R.

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