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Date: Fri, 19 Sep 2014 21:30:36 +0300 From: Grygorii Strashko <grygorii.strashko@...com> To: Mark Salter <msalter@...hat.com>, Will Deacon <will.deacon@....com> CC: Catalin Marinas <Catalin.Marinas@....com>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>, "jcm@...hat.com" <jcm@...hat.com> Subject: Re: [PATCH] arm64/pci: fix dma coherency inheritance for PCI devices Hi Mark, On 09/19/2014 07:42 PM, Mark Salter wrote: > On Fri, 2014-09-19 at 17:28 +0100, Will Deacon wrote: >> On Fri, Sep 19, 2014 at 04:51:26PM +0100, Mark Salter wrote: >>> The default dma_ops for devices on arm64 systems are noncoherent in >>> nature and rely upon special operations and bounce buffers to >>> perform a device DMA operation to/from memory. Some drivers rely >>> upon coherent operations involving suitably capable hardware. In >>> this case, a "dma-coherent" property will exist on the corresponding >>> Device Tree node for the bridge device, or one of its ancestors. >>> This patch adds support for applying a DMA coherent dma_ops for >>> PCI devices in the case of such a property. >>> >>> Signed-off-by: Jon Masters <jcm@...hat.com> >>> [added search for device with of_node] >>> Signed-off-by: Mark Salter <msalter@...hat.com> >>> --- >>> arch/arm64/mm/dma-mapping.c | 21 +++++++++++++++++++-- >>> 1 file changed, 19 insertions(+), 2 deletions(-) >>> >>> diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c >>> index 4164c5a..0e26bd7 100644 >>> --- a/arch/arm64/mm/dma-mapping.c >>> +++ b/arch/arm64/mm/dma-mapping.c >>> @@ -23,10 +23,12 @@ >>> #include <linux/dma-mapping.h> >>> #include <linux/dma-contiguous.h> >>> #include <linux/of.h> >>> +#include <linux/of_address.h> >>> #include <linux/platform_device.h> >>> #include <linux/vmalloc.h> >>> #include <linux/swiotlb.h> >>> #include <linux/amba/bus.h> >>> +#include <linux/pci.h> >>> >>> #include <asm/cacheflush.h> >>> >>> @@ -316,8 +318,18 @@ static int dma_bus_notifier(struct notifier_block *nb, >>> if (event != BUS_NOTIFY_ADD_DEVICE) >>> return NOTIFY_DONE; >>> >>> - if (of_property_read_bool(dev->of_node, "dma-coherent")) >>> - set_dma_ops(dev, &coherent_swiotlb_dma_ops); >>> + /* >>> + * Some devices won't have an of_node but a bus controller/bridge will. >>> + * Search up the device chain until we find an of_node to check. >>> + */ >>> + while (dev) { >>> + if (dev->of_node) { >>> + if (of_dma_is_coherent(dev->of_node)) >>> + set_dma_ops(_dev, &coherent_swiotlb_dma_ops); >>> + break; >>> + } >>> + dev = dev->parent; >>> + } >> >> Hmm, how does this interact with of_dma_configure? I don't think the >> dma-coherent property is inherited there, so I'm uneasy about doing this for >> buses other than PCI (i.e. the platform bus). > > of_dma_configure() only gets called for platform bus and it It's going to be used for AMBA bus too - "[PATCH] of: amba: use of_dma_configure for AMBA devices" http://www.spinics.net/lists/arm-kernel/msg363169.html > uses of_dma_is_coherent() which searches device ancestors for > dma-coherent property. But it uses set_arch_dma_coherent_ops() of_dma_is_coherent() will search from current Device node and all its ancestors. > which is a no-op on arm64 now. Catalin mentions this in another > thread: https://lkml.org/lkml/2014/9/15/363 > > So maybe we should fix set_arch_dma_coherent_ops() and drop > platform bus from the notifier handler. Yes. That will allow you to drop platform bus notifier handler. Actually, if patch "[PATCH] of: amba: use of_dma_configure for AMBA devices" will be merged then notifier for AMBA bus can be dropped too. > >> >> In other words, we should move to using of_dma_configure for the platform >> and amba buses, and have a separate notifier for the PCI bus. Is it likely >> that people will have a mixture of coherent and non-coherent devices behind >> the same host controller? >> Also, there is a patch which updates DT documentation for DMA properties, but it's not been merged accidentally :( "Re: [PATCH] dt/documentation: add specification of dma bus information" https://lkml.org/lkml/2014/6/22/144 Regards, -grygorii -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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