From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932714Ab0BPH6o (ORCPT ); Tue, 16 Feb 2010 02:58:44 -0500 Received: from devils.ext.ti.com ([198.47.26.153]:51072 "EHLO devils.ext.ti.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754493Ab0BPH6n convert rfc822-to-8bit (ORCPT ); Tue, 16 Feb 2010 02:58:43 -0500 From: "Shilimkar, Santosh" To: Catalin Marinas , Pavel Machek , Greg KH , Russell King - ARM Linux CC: 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 13:27:53 +0530 Subject: RE: USB mass storage and ARM cache coherency Thread-Topic: USB mass storage and ARM cache coherency Thread-Index: Acqoskzu3x2YdA6rS5S6M3u8UyjhAAGKPpUg Message-ID: References: <20100208065519.GE1290@ucw.cz> <1265622676.4020.19.camel@pc1117.cambridge.arm.com> <20100208105209.GA31671@atrey.karlin.mff.cuni.cz> <1265628483.4020.63.camel@pc1117.cambridge.arm.com> In-Reply-To: <1265628483.4020.63.camel@pc1117.cambridge.arm.com> 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: 8BIT MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > -----Original Message----- > From: linux-arm-kernel-bounces@lists.infradead.org [mailto:linux-arm-kernel- > bounces@lists.infradead.org] On Behalf Of Catalin Marinas > Sent: Monday, February 08, 2010 4:58 PM > To: Pavel Machek > Cc: Matthew Dharm; Sergei Shtylyov; Ming Lei; Sebastian Siewior; linux-usb@vger.kernel.org; linux- > kernel; Greg KH; linux-arm-kernel > Subject: Re: USB mass storage and ARM cache coherency > > On Mon, 2010-02-08 at 10:52 +0000, Pavel Machek wrote: > > > On Mon, 2010-02-08 at 06:55 +0000, Pavel Machek wrote: > > > > > > So, let's put this in the HCD drivers and be done with it. > > > > > > > > > > The patch below is what fixes the I-D cache incoherency issues on ARM. I > > > > > don't particularly like the solution but it seems to be the only one > > > > > available. > > > > > > > > Really? It looks like arm should just flush the caches when mapping > > > > executable page to the userspace.... you can't expect all the drivers > > > > to be modified like that... > > > > > > We could of course flush the caches every time we get a page fault but > > > that's far from optimal, especially since DMA-capable drivers to do > > > not > > > > Maybe far for optimal, but it is something that should be done, > > _first_. Correctness is more important than performance, and you can't > > expect all drivers to behave like you want them. > > I wouldn't call heavy cache flushing "correctness". We could as well > disable the caches so that it is fully coherent. > > The arch code follows an API defined in cachetlb.txt but the PIO drivers > don't (some do, like mmci.c). It may be inconvenient to call > flush_dcache_page() in the driver, hence I started a discussion on > linux-arch on a PIO mapping API that x86 or other fully coherent > architectures can leave it as no-ops. > > > Then you can add optimalizations not to do the flushes on drivers you > > audited and where you care... > > Sorry but that's not really feasible (unless I don't fully understand > what you mean) - if we do the cache flushing on the fault handling path > in the arch code, there is no way for the arch code to know what driver > is doing, unless we make this conditionally compiled with something like > CONFIG_ARCH_NEEDS_HEAVY_FLUSHING. Continuing on the USB issue w.r.t cache coherency, the usb host code is violating the buffer ownership rules of streaming APIs from dma and non-dma transfers point if view. We have a below temporary patch to get around the issue and probably it needs to be fixed in the right way in the stack because some controllers may not have PIO option even for control transfers. (e.g. Synopsis EHCI controller) From: Maulik Mankad USB: Avoid DMA map/unmap of control transfer buffers. This patch avoids the DMA mapping of buffers for control transfers. Signed-off-by: Maulik Mankad --- Index: omap4_integration/drivers/usb/core/hcd.c =================================================================== --- omap4_integration.orig/drivers/usb/core/hcd.c +++ omap4_integration/drivers/usb/core/hcd.c @@ -1274,6 +1274,10 @@ static int map_urb_for_dma(struct usb_hc if (is_root_hub(urb->dev)) return 0; + if (usb_endpoint_xfer_control(&urb->ep->desc)) + urb->transfer_flags = URB_NO_SETUP_DMA_MAP | + URB_NO_TRANSFER_DMA_MAP; + if (usb_endpoint_xfer_control(&urb->ep->desc) && !(urb->transfer_flags & URB_NO_SETUP_DMA_MAP)) { if (hcd->self.uses_dma) { From mboxrd@z Thu Jan 1 00:00:00 1970 From: santosh.shilimkar@ti.com (Shilimkar, Santosh) Date: Tue, 16 Feb 2010 13:27:53 +0530 Subject: USB mass storage and ARM cache coherency In-Reply-To: <1265628483.4020.63.camel@pc1117.cambridge.arm.com> References: <20100208065519.GE1290@ucw.cz> <1265622676.4020.19.camel@pc1117.cambridge.arm.com> <20100208105209.GA31671@atrey.karlin.mff.cuni.cz> <1265628483.4020.63.camel@pc1117.cambridge.arm.com> Message-ID: To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org > -----Original Message----- > From: linux-arm-kernel-bounces at lists.infradead.org [mailto:linux-arm-kernel- > bounces at lists.infradead.org] On Behalf Of Catalin Marinas > Sent: Monday, February 08, 2010 4:58 PM > To: Pavel Machek > Cc: Matthew Dharm; Sergei Shtylyov; Ming Lei; Sebastian Siewior; linux-usb at vger.kernel.org; linux- > kernel; Greg KH; linux-arm-kernel > Subject: Re: USB mass storage and ARM cache coherency > > On Mon, 2010-02-08 at 10:52 +0000, Pavel Machek wrote: > > > On Mon, 2010-02-08 at 06:55 +0000, Pavel Machek wrote: > > > > > > So, let's put this in the HCD drivers and be done with it. > > > > > > > > > > The patch below is what fixes the I-D cache incoherency issues on ARM. I > > > > > don't particularly like the solution but it seems to be the only one > > > > > available. > > > > > > > > Really? It looks like arm should just flush the caches when mapping > > > > executable page to the userspace.... you can't expect all the drivers > > > > to be modified like that... > > > > > > We could of course flush the caches every time we get a page fault but > > > that's far from optimal, especially since DMA-capable drivers to do > > > not > > > > Maybe far for optimal, but it is something that should be done, > > _first_. Correctness is more important than performance, and you can't > > expect all drivers to behave like you want them. > > I wouldn't call heavy cache flushing "correctness". We could as well > disable the caches so that it is fully coherent. > > The arch code follows an API defined in cachetlb.txt but the PIO drivers > don't (some do, like mmci.c). It may be inconvenient to call > flush_dcache_page() in the driver, hence I started a discussion on > linux-arch on a PIO mapping API that x86 or other fully coherent > architectures can leave it as no-ops. > > > Then you can add optimalizations not to do the flushes on drivers you > > audited and where you care... > > Sorry but that's not really feasible (unless I don't fully understand > what you mean) - if we do the cache flushing on the fault handling path > in the arch code, there is no way for the arch code to know what driver > is doing, unless we make this conditionally compiled with something like > CONFIG_ARCH_NEEDS_HEAVY_FLUSHING. Continuing on the USB issue w.r.t cache coherency, the usb host code is violating the buffer ownership rules of streaming APIs from dma and non-dma transfers point if view. We have a below temporary patch to get around the issue and probably it needs to be fixed in the right way in the stack because some controllers may not have PIO option even for control transfers. (e.g. Synopsis EHCI controller) From: Maulik Mankad USB: Avoid DMA map/unmap of control transfer buffers. This patch avoids the DMA mapping of buffers for control transfers. Signed-off-by: Maulik Mankad --- Index: omap4_integration/drivers/usb/core/hcd.c =================================================================== --- omap4_integration.orig/drivers/usb/core/hcd.c +++ omap4_integration/drivers/usb/core/hcd.c @@ -1274,6 +1274,10 @@ static int map_urb_for_dma(struct usb_hc if (is_root_hub(urb->dev)) return 0; + if (usb_endpoint_xfer_control(&urb->ep->desc)) + urb->transfer_flags = URB_NO_SETUP_DMA_MAP | + URB_NO_TRANSFER_DMA_MAP; + if (usb_endpoint_xfer_control(&urb->ep->desc) && !(urb->transfer_flags & URB_NO_SETUP_DMA_MAP)) { if (hcd->self.uses_dma) {