On 09/19/2014 12:28 PM, 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 <j...@redhat.com>
>> [added search for device with of_node]
>> Signed-off-by: Mark Salter <msal...@redhat.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).
>
> 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?
Right. My original internal patch had a separate method for the PCI bus
rather than rolling these back into one...but I suggested to Mark that I
thought Catalin and you wanted this rolled back into one. If you'd
rather there be two, well that's really easy as we know that works.
Jon.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
