Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756706Ab0BBRL3 (ORCPT ); Tue, 2 Feb 2010 12:11:29 -0500 Received: from iolanthe.rowland.org ([192.131.102.54]:51681 "HELO iolanthe.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1756298Ab0BBRL1 (ORCPT ); Tue, 2 Feb 2010 12:11:27 -0500 Date: Tue, 2 Feb 2010 12:11:25 -0500 (EST) From: Alan Stern X-X-Sender: stern@iolanthe.rowland.org To: Oliver Neukum cc: Catalin Marinas , Matthew Dharm , Sergei Shtylyov , Ming Lei , , linux-kernel , Sebastian Siewior , Greg KH Subject: Re: USB mass storage and ARM cache coherency In-Reply-To: <201002021408.51851.oliver@neukum.org> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1612 Lines: 35 On Tue, 2 Feb 2010, Oliver Neukum wrote: > Am Dienstag, 2. Februar 2010 13:39:35 schrieb Catalin Marinas: > > > For storage that is correct. But what about other sources of pages, > > > for example iSCSI? > > > > In the iSCSI case, does the HCD driver write directly to a page cache > > page? Or it just fills in network packets that are copied to page cache > > pages by the iSCSI code (sorry, I'm not familiar with this part of the > > kernel). If the latter, the cache flushing in the HCD driver would not > > help and it needs to be done in the iSCSI code. > > As far as I can tell iSCSI does a private copy. But I don't know how > many methods to transfer code pages over USB exist. I'd say the > conservative solution is to flush for everything but control transfers. This doesn't make any sense. Nobody would ever use isochronous transfers to store data into a code page because isochronous is unreliable. (Audio isn't a counterexample -- audio data may be mapped to userspace, but only to data pages, not code pages. And the problem here is to maintain consistency between the D and I caches.) In principle interrupt transfers could be used, but it is most unlikely. They are intended for bounded-latency transfers, not transfers of potentially large amounts of data. The only transfer type that makes sense to worry about is bulk. Alan Stern -- 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/