On Thu, Feb 20, 2020 at 05:21:35PM +0000, Robin Murphy wrote:

quoted

@@ -196,10 +192,15 @@ void *dma_direct_alloc_pages(struct device *dev, size_t size,
    	memset(ret, 0, size);
  -	if (IS_ENABLED(CONFIG_ARCH_HAS_UNCACHED_SEGMENT) &&
-	    dma_alloc_need_uncached(dev, attrs)) {
+	if (dma_alloc_need_uncached(dev, attrs)) {
  		arch_dma_prep_coherent(page, size);
-		ret = uncached_kernel_address(ret);
+
+		if (IS_ENABLED(CONFIG_ARCH_HAS_DMA_SET_UNCACHED)) {
+			if (!arch_dma_set_uncached(ret, size))
+				goto out_free_pages;
+		} else if (IS_ENABLED(CONFIG_ARCH_HAS_UNCACHED_SEGMENT)) {
+			ret = uncached_kernel_address(ret);

Hmm, would we actually need to keep ARCH_HAS_UNCACHED_SEGMENT? If 
arch_dma_set_uncached() returned void*/ERR_PTR instead, then it could work 
for both cases (with arch_dma_clear_uncached() being a no-op for segments).

Yes, I think so.  I was a little worried about what to do with
cached_kernel_address() in that scheme, but it turns out with the recent
round of dma-direct cleanup that is actually entirely unused now.

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