[RFC PATCH] ARM64: PCI: inherit root controller's dma-coherent

[Jon Masters]

Ming,

Thanks for reviving this patch. We carry a similar one internally for Storm currently to handle the Mellanox part that you are trying to use with Trusty as well. There's also an ACPI variant based upon the _CCA provided for the root complex but the eventual upstream solution needs to be a bit more nuanced on AArch64 since PCI devices can imply properties of coherency in e.g. snoopable capability. So while this is an ok default/fallback/initial patch, PCI on AArch64 will need a bit more than this. We're looking at this at the moment (in addition to having the ACPI specification clarified to indicate that there is no safe default assumption, requiring that DMA masters always indicate their coherency or otherwise via a _CCA whether true or false).

Jon.

-- 
Computer Architect | Sent from my 64-bit #ARM Powered Tablet

> On Nov 27, 2014, at 12:41 AM, Ming Lei <ming.lei at canonical.com> wrote:
> 
> This patch sets pci device's dma ops as coherent if the root
> controller is dma-coherent.
> 
> This patch fixes the bug in below link:
> 
>    https://bugs.launchpad.net/bugs/1386490
> 
> Cc: Catalin Marinas <Catalin.Marinas at arm.com>
> Cc: Jon Masters <jcm at redhat.com>
> Cc: Dann Frazier <dann.frazier at canonical.com>
> Signed-off-by: Ming Lei <ming.lei at canonical.com>
> ---
> arch/arm64/kernel/pci.c |   17 +++++++++++++++++
> 1 file changed, 17 insertions(+)
> 
> diff --git a/arch/arm64/kernel/pci.c b/arch/arm64/kernel/pci.c
> index ce5836c..4b6444a 100644
> --- a/arch/arm64/kernel/pci.c
> +++ b/arch/arm64/kernel/pci.c
> @@ -16,6 +16,7 @@
> #include <linux/mm.h>
> #include <linux/of_pci.h>
> #include <linux/of_platform.h>
> +#include <linux/of_address.h>
> #include <linux/slab.h>
> 
> #include <asm/pci-bridge.h>
> @@ -37,6 +38,21 @@ resource_size_t pcibios_align_resource(void *data, const struct resource *res,
>    return res->start;
> }
> 
> +/* Inherit root controller's dma coherent ops */
> +static void pci_dma_config(struct pci_dev *dev)
> +{
> +    struct pci_bus *bus = dev->bus;
> +    struct device *host;
> +
> +    while (!pci_is_root_bus(bus)) {
> +        bus = bus->parent;
> +    }
> +
> +    host = bus->dev.parent->parent;
> +    if (of_dma_is_coherent(host->of_node))
> +        set_arch_dma_coherent_ops(&dev->dev);
> +}
> +
> /*
>  * Try to assign the IRQ number from DT when adding a new device
>  */
> @@ -44,6 +60,7 @@ int pcibios_add_device(struct pci_dev *dev)
> {
>    dev->irq = of_irq_parse_and_map_pci(dev, 0, 0);
> 
> +    pci_dma_config(dev);
>    return 0;
> }
> 
> -- 
> 1.7.9.5
>