Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1753885AbaA0PZG (ORCPT <rfc822;w@1wt.eu>);
	Mon, 27 Jan 2014 10:25:06 -0500
Received: from trinity.fluff.org ([89.16.178.74]:49190 "EHLO trinity.fluff.org"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1753500AbaA0PY7 (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
	Mon, 27 Jan 2014 10:24:59 -0500
Date: Mon, 27 Jan 2014 15:24:57 +0000
From: Ben Dooks <ben@trinity.fluff.org>
To: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Cc: linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-mmc@vger.kernel.org, dmaengine@vger.kernel.org
Subject: Re: [Q] block / zynq: DMA bouncing
Message-ID: <20140127152457.GA1073@trinity.fluff.org>
References: <Pine.LNX.4.64.1401271549280.23931@axis700.grange>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <Pine.LNX.4.64.1401271549280.23931@axis700.grange>
X-Disclaimer: These are my views alone.
X-URL: http://www.fluff.org/
User-Agent: Mutt/1.5.20 (2009-06-14)
X-SA-Exim-Connect-IP: <locally generated>
X-SA-Exim-Mail-From: ben@trinity.fluff.org
X-SA-Exim-Scanned: No (on trinity.fluff.org); SAEximRunCond expanded to false
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Mon, Jan 27, 2014 at 04:13:56PM +0100, Guennadi Liakhovetski wrote:
> Hi all,
> 
> I'm working on an MMC driver with a DMA capability. All has been working 
> well, until at some point I've got a bus error, when the mmc driver had 
> been handed in a buffer at 0x3000 physical RAM address. The reason is, 
> that on Zynq arch bus masters cannot access RAM below 0x80000. Therefore 
> my question: how shall I configure this in software?
> 
> The way I found was to use ARM-specific struct dmabounce_device_info and 
> implement its .needs_bounce() method to return true for those addresses. 
> Is this the right way or is there a better / more straight-forward one?
> 
> To do the above I have to enable CONFIG_DMABOUNCE, which then selects 
> CONFIG_ZONE_DMA. Having done just that I suddenly discover, that 0x3000 
> buffers aren't used any more, so, I cannot actually verify my 
> implementation :) Looking at ZONE_DMA it looks like it is still covering 
> the whole RAM range (/proc/zoneinfo shows start_pfn=0 in zone DMA), so, I 
> don't see why 0x3000 should be excluded now.
> 
> So, is using the .needs_bounce() method the correct way to support DMA on 
> this arch or is there a better one?

I have a similar issue with Renesas R8A7790 where there is a bus bridge
that can only deal with transactions to one half of the available RAM.

-- 
Ben Dooks, ben@fluff.org, http://www.fluff.org/ben/

Large Hadron Colada: A large Pina Colada that makes the universe disappear.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/