Re: [PATCH 4/7] dma-direct: provide generic support for uncached kernel segments
From: Paul Burton <hidden>
Date: 2019-05-01 17:19:02
Also in:
linux-iommu, linux-mips, lkml
Hi Christoph, On Tue, Apr 30, 2019 at 07:00:29AM -0400, Christoph Hellwig wrote:
quoted hunk ↗ jump to hunk
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