From mboxrd@z Thu Jan 1 00:00:00 1970 From: James Bottomley Subject: Re: [patch 5/6] ps3: BD/DVD/CD-ROM Storage Driver Date: Fri, 13 Jul 2007 09:34:30 -0400 Message-ID: <1184333670.3402.17.camel@localhost.localdomain> References: <20070704132212.726923000@pademelon.sonytel.be> <20070704132346.591348000@pademelon.sonytel.be> <1184331741.3402.13.camel@localhost.localdomain> <20070713130508.GQ5328@kernel.dk> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Return-path: Received: from hancock.steeleye.com ([71.30.118.248]:38411 "EHLO hancock.sc.steeleye.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S932781AbXGMNeb (ORCPT ); Fri, 13 Jul 2007 09:34:31 -0400 In-Reply-To: Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: Geert Uytterhoeven Cc: Jens Axboe , Paul Mackerras , Alessandro Rubini , linuxppc-dev@ozlabs.org, linux-kernel@vger.kernel.org, linux-scsi@vger.kernel.org, Geoff Levand On Fri, 2007-07-13 at 15:25 +0200, Geert Uytterhoeven wrote: > kmap() just returns page_address() on ppc64, as there's no highmem. > kunmap() is a no-op. > So technically I could just use page_address() directly, but Christoph > wanted > me to keep the kmap()/kunmap() sequence because it's considered a good > practice. The point isn't what kmap and kunmap do ... it's the addresses they return. By and large, a kernel virtual address for a page is different from the user virtual address. If the cache is virtually indexed you get different cache lines for the same page ... and that sets you up with aliases you need to resolve. parisc is the same ... our kmap/kunmap are nops as well, but our kernel virtual addresses are still different from the user virtual ones. James