In-Reply-To: <adaodrgb7uq.fsf@cisco.com>
Subject: Re: [openib-general] [PATCH 2.6.19 2/4] ehca: hcp_phyp.c: correct page
 mapping in 64k page mode
To: "Roland Dreier" <rdreier@cisco.com>
Cc: linux-kernel@vger.kernel.org, linuxppc-dev@ozlabs.org,
       openib-general@openib.org, openib-general-bounces@openib.org,
       "Paul Mackerras" <paulus@samba.org>
Message-ID: <OF75FFAC00.E43450CA-ONC1257222.002A402A-C1257222.002AB9BD@de.ibm.com>
From: Christoph Raisch <RAISCH@de.ibm.com>
Date: Fri, 10 Nov 2006 08:49:48 +0100
MIME-Version: 1.0
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Sender: linux-kernel-owner@vger.kernel.org
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> 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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