Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753741AbaFXM15 (ORCPT ); Tue, 24 Jun 2014 08:27:57 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:44846 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752798AbaFXM14 (ORCPT ); Tue, 24 Jun 2014 08:27:56 -0400 Message-ID: <53A96EC5.3030701@canonical.com> Date: Tue, 24 Jun 2014 14:27:49 +0200 From: Maarten Lankhorst User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.5.0 MIME-Version: 1.0 To: Alexandre Courbot , Alexandre Courbot CC: David Airlie , "nouveau@lists.freedesktop.org" , "linux-kernel@vger.kernel.org" , "dri-devel@lists.freedesktop.org" , Ben Skeggs , "linux-tegra@vger.kernel.org" , Russell King - ARM Linux , "linux-arm-kernel@lists.infradead.org" Subject: Re: [Nouveau] [PATCH v2 2/3] drm/ttm: introduce dma cache sync helpers References: <1403603667-11302-1-git-send-email-acourbot@nvidia.com> <1403603667-11302-3-git-send-email-acourbot@nvidia.com> <20140624100220.GK32514@n2100.arm.linux.org.uk> <53A953E6.2030503@nvidia.com> <53A95910.20104@nvidia.com> In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org op 24-06-14 14:23, Alexandre Courbot schreef: > On Tue, Jun 24, 2014 at 7:55 PM, Alexandre Courbot wrote: >> On 06/24/2014 07:33 PM, Alexandre Courbot wrote: >>> On 06/24/2014 07:02 PM, Russell King - ARM Linux wrote: >>>> On Tue, Jun 24, 2014 at 06:54:26PM +0900, Alexandre Courbot wrote: >>>>> From: Lucas Stach >>>>> >>>>> On architectures for which access to GPU memory is non-coherent, >>>>> caches need to be flushed and invalidated explicitly at the >>>>> appropriate places. Introduce two small helpers to make things >>>>> easy for TTM-based drivers. >>>> >>>> Have you run this with DMA API debugging enabled? I suspect you haven't, >>>> and I recommend that you do. >>> >>> # cat /sys/kernel/debug/dma-api/error_count >>> 162621 >>> >>> (╯°□°）╯︵ ┻━┻) >> >> *puts table back on its feet* >> >> So, yeah - TTM memory is not allocated using the DMA API, hence we cannot >> use the DMA API to sync it. Thanks Russell for pointing it out. >> >> The only alternative I see here is to flush the CPU caches when syncing for >> the device, and invalidate them for the other direction. Of course if the >> device has caches on its side as well the opposite operation must also be >> done for it. Guess the only way is to handle it all by ourselves here. :/ > ... and it really sucks. Basically if we cannot use the DMA API here > we will lose the convenience of having a portable API that does just > the right thing for the underlying platform. Without it we would have > to duplicate arm_iommu_sync_single_for_cpu/device() and we would only > have support for ARM. > > The usage of the DMA API that we are doing might be illegal, but in > essence it does exactly what we need - at least for ARM. What are the > alternatives? Convert TTM to use the dma api? :-) ~Maarten -- 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/