From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from hancock.sc.steeleye.com (hancock.steeleye.com [71.30.118.248]) by ozlabs.org (Postfix) with ESMTP id 39153DDF0A for ; Fri, 13 Jul 2007 23:34:32 +1000 (EST) Subject: Re: [patch 5/6] ps3: BD/DVD/CD-ROM Storage Driver From: James Bottomley To: Geert Uytterhoeven In-Reply-To: References: <20070704132212.726923000@pademelon.sonytel.be> <20070704132346.591348000@pademelon.sonytel.be> <1184331741.3402.13.camel@localhost.localdomain> <20070713130508.GQ5328@kernel.dk> Content-Type: text/plain Date: Fri, 13 Jul 2007 09:34:30 -0400 Message-Id: <1184333670.3402.17.camel@localhost.localdomain> Mime-Version: 1.0 Cc: linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org, Alessandro Rubini , linuxppc-dev@ozlabs.org, Paul Mackerras , Jens Axboe List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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