dma-direct: refactor the !coherent checks in dma_direct_alloc

Add a big central !dev_is_dma_coherent(dev) block to deal with as much
as of the uncached allocation schemes and document the schemes a bit
better.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>

diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
index 0110466..f9658fe 100644 (file)
--- a/kernel/dma/direct.c
+++ b/kernel/dma/direct.c
@@ -201,29 +201,49 @@ void *dma_direct_alloc(struct device *dev, size_t size,
            !force_dma_unencrypted(dev) && !is_swiotlb_for_alloc(dev))
                return dma_direct_alloc_no_mapping(dev, size, dma_handle, gfp);
 
-       if (!IS_ENABLED(CONFIG_ARCH_HAS_DMA_SET_UNCACHED) &&
-           !IS_ENABLED(CONFIG_DMA_DIRECT_REMAP) &&
-           !IS_ENABLED(CONFIG_DMA_GLOBAL_POOL) &&
-           !dev_is_dma_coherent(dev) &&
-           !is_swiotlb_for_alloc(dev))
-               return arch_dma_alloc(dev, size, dma_handle, gfp, attrs);
+       if (!dev_is_dma_coherent(dev)) {
+               /*
+                * Fallback to the arch handler if it exists.  This should
+                * eventually go away.
+                */
+               if (!IS_ENABLED(CONFIG_ARCH_HAS_DMA_SET_UNCACHED) &&
+                   !IS_ENABLED(CONFIG_DMA_DIRECT_REMAP) &&
+                   !IS_ENABLED(CONFIG_DMA_GLOBAL_POOL) &&
+                   !is_swiotlb_for_alloc(dev))
+                       return arch_dma_alloc(dev, size, dma_handle, gfp,
+                                             attrs);
 
-       if (IS_ENABLED(CONFIG_DMA_GLOBAL_POOL) &&
-           !dev_is_dma_coherent(dev))
-               return dma_alloc_from_global_coherent(dev, size, dma_handle);
+               /*
+                * If there is a global pool, always allocate from it for
+                * non-coherent devices.
+                */
+               if (IS_ENABLED(CONFIG_DMA_GLOBAL_POOL))
+                       return dma_alloc_from_global_coherent(dev, size,
+                                       dma_handle);
+
+               /*
+                * Otherwise remap if the architecture is asking for it.  But
+                * given that remapping memory is a blocking operation we'll
+                * instead have to dip into the atomic pools.
+                */
+               remap = IS_ENABLED(CONFIG_DMA_DIRECT_REMAP);
+               if (remap) {
+                       if (!gfpflags_allow_blocking(gfp) &&
+                           !is_swiotlb_for_alloc(dev))
+                               return dma_direct_alloc_from_pool(dev, size,
+                                               dma_handle, gfp);
+               } else {
+                       if (IS_ENABLED(CONFIG_ARCH_HAS_DMA_SET_UNCACHED))
+                               set_uncached = true;
+               }
+       }
 
        /*
-        * Remapping or decrypting memory may block. If either is required and
-        * we can't block, allocate the memory from the atomic pools.
-        * If restricted DMA (i.e., is_swiotlb_for_alloc) is required, one must
-        * set up another device coherent pool by shared-dma-pool and use
-        * dma_alloc_from_dev_coherent instead.
+        * Decrypting memory may block, so allocate the memory from the atomic
+        * pools if we can't block.
         */
        if (IS_ENABLED(CONFIG_DMA_COHERENT_POOL) &&
-           !gfpflags_allow_blocking(gfp) &&
-           (force_dma_unencrypted(dev) ||
-            (IS_ENABLED(CONFIG_DMA_DIRECT_REMAP) &&
-             !dev_is_dma_coherent(dev))) &&
+           force_dma_unencrypted(dev) && !gfpflags_allow_blocking(gfp) &&
            !is_swiotlb_for_alloc(dev))
                return dma_direct_alloc_from_pool(dev, size, dma_handle, gfp);
 
@@ -231,10 +251,7 @@ void *dma_direct_alloc(struct device *dev, size_t size,
        page = __dma_direct_alloc_pages(dev, size, gfp & ~__GFP_ZERO);
        if (!page)
                return NULL;
-
-       if (!dev_is_dma_coherent(dev) && IS_ENABLED(CONFIG_DMA_DIRECT_REMAP)) {
-               remap = true;
-       } else if (PageHighMem(page)) {
+       if (PageHighMem(page)) {
                /*
                 * Depending on the cma= arguments and per-arch setup,
                 * dma_alloc_contiguous could return highmem pages.
@@ -246,9 +263,8 @@ void *dma_direct_alloc(struct device *dev, size_t size,
                        goto out_free_pages;
                }
                remap = true;
-       } else if (!dev_is_dma_coherent(dev) &&
-                  IS_ENABLED(CONFIG_ARCH_HAS_DMA_SET_UNCACHED))
-               set_uncached = true;
+               set_uncached = false;
+       }
 
        if (remap) {
                /* remove any dirty cache lines on the kernel alias */