Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756984AbZD0OjX (ORCPT ); Mon, 27 Apr 2009 10:39:23 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755951AbZD0OjG (ORCPT ); Mon, 27 Apr 2009 10:39:06 -0400 Received: from mail-qy0-f180.google.com ([209.85.221.180]:53313 "EHLO mail-qy0-f180.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756658AbZD0OjE (ORCPT ); Mon, 27 Apr 2009 10:39:04 -0400 X-Greylist: delayed 470 seconds by postgrey-1.27 at vger.kernel.org; Mon, 27 Apr 2009 10:39:04 EDT DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:sender:in-reply-to:references:date :x-google-sender-auth:message-id:subject:from:to:cc:content-type :content-transfer-encoding; b=M9xhp/Sd4KQOlAcDQEnBEgfNeZFFyoz39OaRPLOlZTaWEKXdGHwUAqb2A27v/7/5ER rqbSLRBw5HczCnu68lxIfMtVpUxzWKojCaaJueKYyr4/FE5VHmvC8HDL+GkQSu7Cgm5g m4d5+nEWrNtPGCX0DP80KX7/hgSoD5uR8t2Tc= MIME-Version: 1.0 In-Reply-To: References: <20090424183517.GB23140@ovro.caltech.edu> Date: Mon, 27 Apr 2009 09:31:12 -0500 X-Google-Sender-Auth: be36beb348c68657 Message-ID: Subject: Re: [PATCH] fsldma: use PCI Read Multiple command From: Timur Tabi To: Liu Dave-R63238 Cc: Ira Snyder , linux-kernel@vger.kernel.org, linuxppc-dev@ozlabs.org, Dan Williams , Li Yang-R58472 , Zhang Wei Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 920 Lines: 22 On Mon, Apr 27, 2009 at 4:09 AM, Liu Dave-R63238 wrote: > You are assuming the PCI memory space is prefetchable( no side effect) > for DMA. > Is it possible that DMA is from non-prefetchable memory space? This should be a safe assumption for this driver. Remember, this driver just does offload memcpy, from one region to another. So the PCI memory that you are reading from should be just a buffer of data, and there should be side-effect of reading it. However, I would like to see a comment at the top of the file warning people that copying from PCI memory will result in prefetched reads. -- Timur Tabi Linux kernel developer at Freescale -- 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/