From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from SMTP02.CITRIX.COM (smtp02.citrix.com [66.165.176.63]) by ozlabs.org (Postfix) with ESMTP id A66F4DE1C8 for ; Fri, 22 May 2009 05:12:08 +1000 (EST) Subject: Re: [PATCH V2 2/3] powerpc: Add support for swiotlb on 32-bit From: Ian Campbell To: Becky Bruce In-Reply-To: References: <1242340949-16369-1-git-send-email-beckyb@kernel.crashing.org> <1242340949-16369-2-git-send-email-beckyb@kernel.crashing.org> <20090519142656T.fujita.tomonori@lab.ntt.co.jp> <19E48A70-3332-423C-ACAD-390F940EE81C@kernel.crashing.org> <4A1592CF.8000208@goop.org> Content-Type: text/plain Date: Thu, 21 May 2009 20:01:37 +0100 Message-ID: <1242932497.25553.230.camel@localhost.localdomain> MIME-Version: 1.0 Cc: FUJITA Tomonori , "linuxppc-dev@ozlabs.org" , Jeremy Fitzhardinge , "linux-kernel@vger.kernel.org" List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Thu, 2009-05-21 at 14:27 -0400, Becky Bruce wrote: > We have both in every case but one, > which is in swiotlb_map_page where we call address_needs_mapping() > without calling range_needs_mapping. The reason it calls address_needs_mapping without range_needs_mapping is that in the swiotlb_force=1 case it would trigger every time. If address_needs_mapping and range_needs_mapping are merged as proposed and they do not subsume the swiotlb_force check (and I don't think they would) then I think this will work fine. > It's not actually clear to me that we need that check, though. Can > someone explain what case that was designed to catch? If map_single fails and returns NULL then we try to use io_tlb_overflow_buffer, if that is somehow not DMA-able (for the particular device) then the check will trigger. I would have thought we could arrange that the overflow buffer is always OK and really if map_page is failing we must be close the edge already. Ian.