Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756623Ab0BPNq7 (ORCPT ); Tue, 16 Feb 2010 08:46:59 -0500 Received: from smtp-out003.kontent.com ([81.88.40.217]:39244 "EHLO smtp-out003.kontent.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756332Ab0BPNq6 (ORCPT ); Tue, 16 Feb 2010 08:46:58 -0500 From: Oliver Neukum To: "Shilimkar, Santosh" Subject: Re: USB mass storage and ARM cache coherency Date: Tue, 16 Feb 2010 14:46:59 +0100 User-Agent: KMail/1.12.2 (Linux/2.6.33-rc6-0.1-default; KDE/4.3.1; x86_64; ; ) Cc: "Russell King - ARM Linux" , Catalin Marinas , Pavel Machek , Greg KH , Matthew Dharm , Sergei Shtylyov , Ming Lei , Sebastian Siewior , "linux-usb@vger.kernel.org" , "linux-kernel" , "linux-arm-kernel" , "Mankad, Maulik Ojas" References: <20100208065519.GE1290@ucw.cz> <201002161432.57705.oliver@neukum.org> In-Reply-To: MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Message-Id: <201002161446.59920.oliver@neukum.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1095 Lines: 24 Am Dienstag, 16. Februar 2010 14:40:45 schrieb Shilimkar, Santosh: > > > If the CPU writes to a DMA_FROM_DEVICE buffer between map and unmap, the > > > writes can sit in the cache, and on unmap, they will be discarded. > > > > > > Cleaning the cache on unmap is not an option; that too can lead to DMA > > > buffer corruption in the DMA case. > > > > I am afraid for these controllers the controller driver must be responsible > > for all DMA and cache issues. Indicating the exact requirements to the > > upper layer would be a battle already lost. > > so the safe choice is not to set has_dma and the generic layer will leave > > the issue to the lower level. > This means don't use dma at all which will almost kill the performance. Why would you be unable to map a buffer in the hcd driver when you know that you'll use DMA? Regards Oliver -- 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/