Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752289AbaGKCfa (ORCPT ); Thu, 10 Jul 2014 22:35:30 -0400 Received: from hqemgate16.nvidia.com ([216.228.121.65]:7685 "EHLO hqemgate16.nvidia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751409AbaGKCf2 (ORCPT ); Thu, 10 Jul 2014 22:35:28 -0400 X-PGP-Universal: processed; by hqnvupgp08.nvidia.com on Thu, 10 Jul 2014 19:28:21 -0700 Message-ID: <53BF4D6B.70904@nvidia.com> Date: Fri, 11 Jul 2014 11:35:23 +0900 From: Alexandre Courbot Organization: NVIDIA User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.6.0 MIME-Version: 1.0 To: Daniel Vetter CC: Ben Skeggs , David Airlie , David Herrmann , Lucas Stach , Thierry Reding , Maarten Lankhorst , , , , , Alexandre Courbot Subject: Re: [Nouveau] [PATCH v4 2/6] drm/nouveau: map pages using DMA API on platform devices References: <1404807961-30530-1-git-send-email-acourbot@nvidia.com> <1404807961-30530-3-git-send-email-acourbot@nvidia.com> <20140710125849.GF17271@phenom.ffwll.local> In-Reply-To: <20140710125849.GF17271@phenom.ffwll.local> X-NVConfidentiality: public Content-Type: text/plain; charset="ISO-8859-1"; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/10/2014 09:58 PM, Daniel Vetter wrote: > On Tue, Jul 08, 2014 at 05:25:57PM +0900, Alexandre Courbot wrote: >> page_to_phys() is not the correct way to obtain the DMA address of a >> buffer on a non-PCI system. Use the DMA API functions for this, which >> are portable and will allow us to use other DMA API functions for >> buffer synchronization. >> >> Signed-off-by: Alexandre Courbot >> --- >> drivers/gpu/drm/nouveau/core/engine/device/base.c | 8 +++++++- >> 1 file changed, 7 insertions(+), 1 deletion(-) >> >> diff --git a/drivers/gpu/drm/nouveau/core/engine/device/base.c b/drivers/gpu/drm/nouveau/core/engine/device/base.c >> index 18c8c7245b73..e4e9e64988fe 100644 >> --- a/drivers/gpu/drm/nouveau/core/engine/device/base.c >> +++ b/drivers/gpu/drm/nouveau/core/engine/device/base.c >> @@ -489,7 +489,10 @@ nv_device_map_page(struct nouveau_device *device, struct page *page) >> if (pci_dma_mapping_error(device->pdev, ret)) >> ret = 0; >> } else { >> - ret = page_to_phys(page); >> + ret = dma_map_page(&device->platformdev->dev, page, 0, >> + PAGE_SIZE, DMA_BIDIRECTIONAL); >> + if (dma_mapping_error(&device->platformdev->dev, ret)) >> + ret = 0; >> } >> >> return ret; >> @@ -501,6 +504,9 @@ nv_device_unmap_page(struct nouveau_device *device, dma_addr_t addr) >> if (nv_device_is_pci(device)) >> pci_unmap_page(device->pdev, addr, PAGE_SIZE, >> PCI_DMA_BIDIRECTIONAL); > > pci_map/unmap alias to dma_unmap/map when called on the underlying struct > device embedded in pci_device (like for platform drivers). Dunno whether > it's worth to track a pointer to the struct device directly and always > call dma_unmap/map. Isn't it (theoretically) possible to have a platform that does not use the DMA API for its PCI implementation and thus requires the pci_* functions to be called? I could not find such a case in -next, which suggests that all PCI platforms have been converted to the DMA API already and that we could indeed refactor this to always use the DMA functions. But at the same time the way we use APIs should not be directed by their implementation, but by their intent - and unless the PCI API has been deprecated in some way (something I am not aware of), the rule is still that you should use it on a PCI device. > > Just drive-by comment since I'm interested in how you solve this - i915 > has similar fun with buffer sharing and coherent and non-coherent > platforms. Although we don't have fun with pci and non-pci based > platforms. Yeah, I am not familiar with i915 but it seems like we are on a similar boat here (excepted ARM is more constrained as to its memory mappings). The strategy in this series is, map buffers used by user-space cached and explicitly synchronize them (since the ownership transition from user to GPU is always clearly performed by syscalls), and use coherent mappings for buffers used by the kernel which are accessed more randomly. This has solved all our coherency issues and resulted in the best performance so far. -- 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/