Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757447Ab0BQP2B (ORCPT ); Wed, 17 Feb 2010 10:28:01 -0500 Received: from cam-admin0.cambridge.arm.com ([217.140.96.50]:62556 "EHLO cam-admin0.cambridge.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757315Ab0BQP2A (ORCPT ); Wed, 17 Feb 2010 10:28:00 -0500 Subject: Re: USB mass storage and ARM cache coherency From: Catalin Marinas To: Benjamin Herrenschmidt Cc: Oliver Neukum , "Shilimkar, Santosh" , Matthew Dharm , Russell King - ARM Linux , Ming Lei , "Mankad, Maulik Ojas" , Sergei Shtylyov , Sebastian Siewior , "linux-usb@vger.kernel.org" , linux-kernel , Pavel Machek , Greg KH , linux-arm-kernel In-Reply-To: <1266397543.16346.264.camel@pasglop> References: <20100208065519.GE1290@ucw.cz> <1265628483.4020.63.camel@pc1117.cambridge.arm.com> <201002160922.47072.oliver@neukum.org> <1266397543.16346.264.camel@pasglop> Content-Type: text/plain; charset="UTF-8" Organization: ARM Limited Date: Wed, 17 Feb 2010 15:27:55 +0000 Message-ID: <1266420475.16707.31.camel@e102109-lin.cambridge.arm.com> Mime-Version: 1.0 X-Mailer: Evolution 2.28.1 Content-Transfer-Encoding: 7bit X-OriginalArrivalTime: 17 Feb 2010 15:27:56.0778 (UTC) FILETIME=[C7CA5CA0:01CAAFE5] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1770 Lines: 40 On Wed, 2010-02-17 at 20:05 +1100, Benjamin Herrenschmidt wrote: > On Tue, 2010-02-16 at 09:22 +0100, Oliver Neukum wrote: > > This seems wrong to me. Buffers for control transfers may be > > transfered > > by DMA, so the caches must be flushed on architectures whose caches > > are not coherent with respect to DMA. > > > > Would you care to elaborate on the exact nature of the bug you are > > fixing? > > I missed part of this thread, so forgive me if I'm a bit off here, but > if the problem is indeed I$/D$ cache coherency vs. PIO transfers, then > this is a long solved issue on other archs such as ppc (and I _think_ > sparc). The thread I started was indeed regarding I/D cache coherency and PIO. But it diverged into DMA issues a few days ago (should have been a new thread). > The way we do it, at least on powerpc which is PIPT, is to keep track on > a per-page basis, whether a given page is clean for execution using > PG_arch1 bit. This bit is cleared when a new page is popped into the > page cache, and we clear it from flush_dcache_page() iirc (you may want > to dbl check I don't have the code at hand right now, or rather, I do > but I'm to lazy to look right now :-) We do the same on ARM. The problem with most (all) HCD drivers that do PIO is that they copy the data to the transfer buffer but there is no call in this driver to flush_dcache_page(). The upper mass storage or filesystem layers don't call this function either, so there isn't anything that would set the PG_arch1 bit. -- Catalin -- 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/