From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1751868AbdJCLnd (ORCPT <rfc822;w@1wt.eu>);
        Tue, 3 Oct 2017 07:43:33 -0400
Received: from verein.lst.de ([213.95.11.211]:43250 "EHLO newverein.lst.de"
        rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
        id S1751604AbdJCLnc (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
        Tue, 3 Oct 2017 07:43:32 -0400
Date: Tue, 3 Oct 2017 13:43:30 +0200
From: Christoph Hellwig <hch@lst.de>
To: Christophe LEROY <christophe.leroy@c-s.fr>
Cc: Christoph Hellwig <hch@lst.de>, iommu@lists.linux-foundation.org,
        Chris Zankel <chris@zankel.net>, Michal Simek <monstr@monstr.eu>,
        linux-ia64@vger.kernel.org, linux-mips@linux-mips.org,
        linux-sh@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
        linux-xtensa@linux-xtensa.org, x86@kernel.org,
        linux-kernel@vger.kernel.org, David Howells <dhowells@redhat.com>,
        Max Filippov <jcmvbkbc@gmail.com>, Guan Xuetao <gxt@mprc.pku.edu.cn>,
        Robin Murphy <robin.murphy@arm.com>,
        Marek Szyprowski <m.szyprowski@samsung.com>
Subject: Re: [PATCH 07/11] powerpc: make dma_cache_sync a no-op
Message-ID: <20171003114330.GA24592@lst.de>
References: <20171003104311.10058-1-hch@lst.de> <20171003104311.10058-8-hch@lst.de> <670a0571-1a36-51a3-db52-64bc61184c35@c-s.fr>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <670a0571-1a36-51a3-db52-64bc61184c35@c-s.fr>
User-Agent: Mutt/1.5.17 (2007-11-01)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Tue, Oct 03, 2017 at 01:24:57PM +0200, Christophe LEROY wrote:
>> powerpc does not implement DMA_ATTR_NON_CONSISTENT allocations, so it
>> doesn't make any sense to do any work in dma_cache_sync given that it
>> must be a no-op when dma_alloc_attrs returns coherent memory.
> What about arch/powerpc/mm/dma-noncoherent.c ?
>
> Powerpc 8xx doesn't have coherent memory.

It doesn't implement the DMA_ATTR_NON_CONSISTENT interface either,
so if it really doesn't have a way to provide dma coherent allocation
(although the code in __dma_alloc_coherent suggests it does provide
dma coherent allocations) I have no idea how it could ever have
worked.