On Thu, Jun 28, 2018 at 05:14:52PM +0300, Eugeniy Paltsev wrote:
> And if we get DMA buffer from ZONE_HIGHMEM memory we need to
> do real flush/invalidate operations on that buffer, which is obviously
> not done by "dma_direct_ops".
>
> So I am not sure about "dma_direct_ops" using - probably we need to
> create our special cache ops like "arc_ioc_ops" which will handle
> ZONE_HIGHMEM case.
FYI, I have a plan to merge dma_direct_ops and dma_noncoherent_ops
and make the decision to use cache flushing run time controllable
with a flag in struct device based on existing dynamic selection
in e.g. arm, arm64 and mips. It will probably take a few more merge
windows to get there, but once it is done you should be able to take
easy advantage of it.
> +++ b/arch/arc/mm/dma.c
> @@ -19,6 +19,7 @@
> #include <linux/dma-noncoherent.h>
> #include <asm/cache.h>
> #include <asm/cacheflush.h>
> +#include <linux/dma-mapping.h>
dma-noncoherent.h already includes dma-mapping.h, so this is not
required.
> - if ((is_isa_arcv2() && ioc_enable) ||
> - (attrs & DMA_ATTR_NON_CONSISTENT))
> + if (attrs & DMA_ATTR_NON_CONSISTENT)
> need_coh = 0;
need_coh is only used twice, it might be cleaner to remove the
variable and just open code the DMA_ATTR_NON_CONSISTENT check.
And for extra points remove the need_kvaddr variable as well.
Also you probably want to do the equivalent change in arch_dma_free
as well.
> +void arch_setup_dma_ops(struct device *dev, u64 dma_base, u64 size,
> + const struct iommu_ops *iommu, bool coherent)
> +{
> + /*
> + * IOC hardware snoops all DMA traffic keeping the caches consistent
> + * with memory - eliding need for any explicit cache maintenance of
> + * DMA buffers - so we can use dma_direct cache ops.
> + */
> + if (is_isa_arcv2() && ioc_enable && coherent) {
> + set_dma_ops(dev, &dma_direct_ops);
> + dev_info(dev, "use dma_direct_ops cache ops\n");
> + } else {
> + set_dma_ops(dev, &dma_noncoherent_ops);
> + dev_info(dev, "use dma_noncoherent_ops cache ops\n");
> + }
> +}
Note that due to your use of asm-generic/dma-mapping.h we already
default to dma_noncoherent_ops if no per-device ops is set. So we
could skip the else branch here I think.
