Hi Christoph,
On Tue, Apr 30, 2019 at 07:00:29AM -0400, Christoph Hellwig wrote:
> diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
> index 2c2772e9702a..d15a535c3e67 100644
> --- a/kernel/dma/direct.c
> +++ b/kernel/dma/direct.c
> @@ -164,6 +164,13 @@ void *dma_direct_alloc_pages(struct device *dev, size_t
> size,
> }
>
> ret = page_address(page);
> +
> + if (IS_ENABLED(CONFIG_ARCH_HAS_UNCACHED_SEGMENT) &&
> + !dev_is_dma_coherent(dev) && !(attrs & DMA_ATTR_NON_CONSISTENT)) {
> + arch_dma_prep_coherent(page, size);
> + ret = uncached_kernel_address(ret);
> + }
> +
> if (force_dma_unencrypted()) {
> set_memory_decrypted((unsigned long)ret, 1 << get_order(size));
> *dma_handle = __phys_to_dma(dev, page_to_phys(page));
> @@ -171,6 +178,7 @@ void *dma_direct_alloc_pages(struct device *dev, size_t
> size,
> *dma_handle = phys_to_dma(dev, page_to_phys(page));
> }
> memset(ret, 0, size);
> +
> return ret;
> }
I'm not so sure about this part though.
On MIPS we currently don't clear the allocated memory with memset. Is
doing that really necessary?
If it is necessary then as-is this code will clear the allocated memory
using uncached writes which will be pretty slow. It would be much more
efficient to perform the memset before arch_dma_prep_coherent() & before
converting ret to an uncached address.
Thanks,
Paul
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