From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752487AbaEBQzG (ORCPT ); Fri, 2 May 2014 12:55:06 -0400 Received: from mail-ie0-f173.google.com ([209.85.223.173]:42528 "EHLO mail-ie0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751782AbaEBQzD (ORCPT ); Fri, 2 May 2014 12:55:03 -0400 Date: Fri, 2 May 2014 10:54:59 -0600 From: Bjorn Helgaas To: Santosh Shilimkar Cc: linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, devicetree@vger.kernel.org, Greg Kroah-Hartman , Russell King , Arnd Bergmann , Olof Johansson , Grant Likely , Rob Herring , Catalin Marinas , Linus Walleij , Grygorii Strashko Subject: Re: [PATCH v3 4/7] of: configure the platform device dma parameters Message-ID: <20140502165459.GA29511@google.com> References: <1398353407-2345-1-git-send-email-santosh.shilimkar@ti.com> <1398353407-2345-5-git-send-email-santosh.shilimkar@ti.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1398353407-2345-5-git-send-email-santosh.shilimkar@ti.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Apr 24, 2014 at 11:30:04AM -0400, Santosh Shilimkar wrote: > Retrieve DMA configuration from DT and setup platform device's DMA > parameters. The DMA configuration in DT has to be specified using > "dma-ranges" and "dma-coherent" properties if supported. > > We setup dma_pfn_offset using "dma-ranges" and dma_coherent_ops > using "dma-coherent" device tree properties. > > The set_arch_dma_coherent_ops macro has to be defined by arch if > it supports coherent dma_ops. Otherwise, set_arch_dma_coherent_ops() is > declared as nop. > > Cc: Greg Kroah-Hartman > Cc: Russell King > Cc: Arnd Bergmann > Cc: Olof Johansson > Cc: Grant Likely > Cc: Rob Herring > Cc: Catalin Marinas > Cc: Linus Walleij > Signed-off-by: Grygorii Strashko > Signed-off-by: Santosh Shilimkar > --- > drivers/of/platform.c | 48 ++++++++++++++++++++++++++++++++++++++++--- > include/linux/dma-mapping.h | 7 +++++++ > 2 files changed, 52 insertions(+), 3 deletions(-) > > diff --git a/drivers/of/platform.c b/drivers/of/platform.c > index 48de98f..270c0b9 100644 > --- a/drivers/of/platform.c > +++ b/drivers/of/platform.c > @@ -187,6 +187,50 @@ struct platform_device *of_device_alloc(struct device_node *np, > EXPORT_SYMBOL(of_device_alloc); > > /** > + * of_dma_configure - Setup DMA configuration > + * @dev: Device to apply DMA configuration > + * > + * Try to get devices's DMA configuration from DT and update it > + * accordingly. > + * > + * In case if platform code need to use own special DMA configuration,it > + * can use Platform bus notifier and handle BUS_NOTIFY_ADD_DEVICE event > + * to fix up DMA configuration. > + */ > +static void of_dma_configure(struct device *dev) > +{ > + u64 dma_addr, paddr, size; > + int ret; > + > + dev->coherent_dma_mask = DMA_BIT_MASK(32); > + if (!dev->dma_mask) > + dev->dma_mask = &dev->coherent_dma_mask; > + > + /* > + * if dma-coherent property exist, call arch hook to setup > + * dma coherent operations. > + */ > + if (of_dma_is_coherent(dev->of_node)) { > + set_arch_dma_coherent_ops(dev); > + dev_dbg(dev, "device is dma coherent\n"); > + } > + > + /* > + * if dma-ranges property doesn't exist - just return else > + * setup the dma offset > + */ > + ret = of_dma_get_range(dev->of_node, &dma_addr, &paddr, &size); > + if ((ret == -ENODEV) || (ret < 0)) { > + dev_dbg(dev, "no dma range information to setup\n"); > + return; > + } > + > + /* DMA ranges found. Calculate and set dma_pfn_offset */ > + dev->dma_pfn_offset = PFN_DOWN(paddr - dma_addr); > + dev_dbg(dev, "dma_pfn_offset(%#08lx)\n", dev->dma_pfn_offset); Is this effectively the same as an IOMMU that applies a constant offset to the bus address? Could or should this be done by adding a simple IOMMU driver instead of adding dma_pfn_offset to struct device? If we had both dma-ranges (and we set dma_pfn_offset as you do here) and an IOMMU, how would the combination work? If the IOMMU driver managed dma_pfn_offset internally, it seems like we'd have two entities dealing with it. If the IOMMU driver doesn't use dma_pfn_offset, it seems like it would be exposing a weird intermediate address space that's not usable by either CPU or device.