Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756403Ab0BPNlg (ORCPT ); Tue, 16 Feb 2010 08:41:36 -0500 Received: from bear.ext.ti.com ([192.94.94.41]:60543 "EHLO bear.ext.ti.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756180Ab0BPNle convert rfc822-to-8bit (ORCPT ); Tue, 16 Feb 2010 08:41:34 -0500 From: "Shilimkar, Santosh" To: Oliver Neukum , Russell King - ARM Linux CC: 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" Date: Tue, 16 Feb 2010 19:10:45 +0530 Subject: RE: USB mass storage and ARM cache coherency Thread-Topic: USB mass storage and ARM cache coherency Thread-Index: AcqvDJIz3paz2VxfSk25VXKmqZQZeQAALBTw Message-ID: References: <20100208065519.GE1290@ucw.cz> <201002161007.20576.oliver@neukum.org> <20100216093946.GA13884@n2100.arm.linux.org.uk> <201002161432.57705.oliver@neukum.org> In-Reply-To: <201002161432.57705.oliver@neukum.org> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: acceptlanguage: en-US Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1676 Lines: 35 > -----Original Message----- > From: Oliver Neukum [mailto:oliver@neukum.org] > Sent: Tuesday, February 16, 2010 7:03 PM > To: Russell King - ARM Linux > Cc: Shilimkar, Santosh; 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 > Subject: Re: USB mass storage and ARM cache coherency > > Am Dienstag, 16. Februar 2010 10:39:46 schrieb Russell King - ARM Linux: > > However, because ARM CPUs can now speculatively prefetch, just leaving it > > at that results in corruption of buffers used for DMA. So we have to > > invalidate DMA_FROM_DEVICE and DMA_BIDIRECTIONAL buffers on unmap to > > ensure coherency with DMA operations. > > > > 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. Regards, Santosh -- 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/