swiotlb: refactor coherent buffer allocation

Factor out a new swiotlb_alloc_buffer helper that allocates DMA coherent
memory from the swiotlb bounce buffer.

This allows to simplify the swiotlb_alloc implemenation that uses
dma_direct_alloc to try to allocate a reachable buffer first.

Signed-off-by: Christoph Hellwig <[email protected]>
Acked-by: Christian König <[email protected]>

Author: Christoph Hellwig

lib/swiotlb.c

@@ -709,75 +709,79 @@ void swiotlb_tbl_sync_single(struct device *hwdev, phys_addr_t tlb_addr,
 }
 EXPORT_SYMBOL_GPL(swiotlb_tbl_sync_single);
 
-void *
-swiotlb_alloc_coherent(struct device *hwdev, size_t size,
-		       dma_addr_t *dma_handle, gfp_t flags)
+static inline bool dma_coherent_ok(struct device *dev, dma_addr_t addr,
+		size_t size)
 {
-	bool warn = !(flags & __GFP_NOWARN);
-	dma_addr_t dev_addr;
-	void *ret;
-	int order = get_order(size);
-	u64 dma_mask = DMA_BIT_MASK(32);
+	u64 mask = DMA_BIT_MASK(32);
 
-	if (hwdev && hwdev->coherent_dma_mask)
-		dma_mask = hwdev->coherent_dma_mask;
+	if (dev && dev->coherent_dma_mask)
+		mask = dev->coherent_dma_mask;
+	return addr + size - 1 <= mask;
+}
 
-	ret = (void *)__get_free_pages(flags, order);
-	if (ret) {
-		dev_addr = swiotlb_virt_to_bus(hwdev, ret);
-		if (dev_addr + size - 1 > dma_mask) {
-			/*
-			 * The allocated memory isn't reachable by the device.
-			 */
-			free_pages((unsigned long) ret, order);
-			ret = NULL;
-		}
-	}
-	if (!ret) {
-		/*
-		 * We are either out of memory or the device can't DMA to
-		 * GFP_DMA memory; fall back on map_single(), which
-		 * will grab memory from the lowest available address range.
-		 */
-		phys_addr_t paddr = map_single(hwdev, 0, size, DMA_FROM_DEVICE,
-					       warn ? 0 : DMA_ATTR_NO_WARN);
-		if (paddr == SWIOTLB_MAP_ERROR)
-			goto err_warn;
+static void *
+swiotlb_alloc_buffer(struct device *dev, size_t size, dma_addr_t *dma_handle,
+		unsigned long attrs)
+{
+	phys_addr_t phys_addr;
 
-		ret = phys_to_virt(paddr);
-		dev_addr = swiotlb_phys_to_dma(hwdev, paddr);
+	if (swiotlb_force == SWIOTLB_NO_FORCE)
+		goto out_warn;
 
-		/* Confirm address can be DMA'd by device */
-		if (dev_addr + size - 1 > dma_mask) {
-			printk("hwdev DMA mask = 0x%016Lx, dev_addr = 0x%016Lx\n",
-			       (unsigned long long)dma_mask,
-			       (unsigned long long)dev_addr);
+	phys_addr = swiotlb_tbl_map_single(dev,
+			swiotlb_phys_to_dma(dev, io_tlb_start),
+			0, size, DMA_FROM_DEVICE, 0);
+	if (phys_addr == SWIOTLB_MAP_ERROR)
+		goto out_warn;
 
-			/*
-			 * DMA_TO_DEVICE to avoid memcpy in unmap_single.
-			 * The DMA_ATTR_SKIP_CPU_SYNC is optional.
-			 */
-			swiotlb_tbl_unmap_single(hwdev, paddr,
-						 size, DMA_TO_DEVICE,
-						 DMA_ATTR_SKIP_CPU_SYNC);
-			goto err_warn;
-		}
-	}
+	*dma_handle = swiotlb_phys_to_dma(dev, phys_addr);
+	if (dma_coherent_ok(dev, *dma_handle, size))
+		goto out_unmap;
 
-	*dma_handle = dev_addr;
-	memset(ret, 0, size);
+	memset(phys_to_virt(phys_addr), 0, size);
+	return phys_to_virt(phys_addr);
 
-	return ret;
+out_unmap:
+	dev_warn(dev, "hwdev DMA mask = 0x%016Lx, dev_addr = 0x%016Lx\n",
+		(unsigned long long)(dev ? dev->coherent_dma_mask : 0),
+		(unsigned long long)*dma_handle);
 
-err_warn:
-	if (warn && printk_ratelimit()) {
-		pr_warn("swiotlb: coherent allocation failed for device %s size=%zu\n",
-			dev_name(hwdev), size);
+	/*
+	 * DMA_TO_DEVICE to avoid memcpy in unmap_single.
+	 * DMA_ATTR_SKIP_CPU_SYNC is optional.
+	 */
+	swiotlb_tbl_unmap_single(dev, phys_addr, size, DMA_TO_DEVICE,
+			DMA_ATTR_SKIP_CPU_SYNC);
+out_warn:
+	if ((attrs & DMA_ATTR_NO_WARN) && printk_ratelimit()) {
+		dev_warn(dev,
+			"swiotlb: coherent allocation failed, size=%zu\n",
+			size);
 		dump_stack();
 	}
-
 	return NULL;
 }
+
+void *
+swiotlb_alloc_coherent(struct device *hwdev, size_t size,
+		       dma_addr_t *dma_handle, gfp_t flags)
+{
+	int order = get_order(size);
+	unsigned long attrs = (flags & __GFP_NOWARN) ? DMA_ATTR_NO_WARN : 0;
+	void *ret;
+
+	ret = (void *)__get_free_pages(flags, order);
+	if (ret) {
+		*dma_handle = swiotlb_virt_to_bus(hwdev, ret);
+		if (dma_coherent_ok(hwdev, *dma_handle, size)) {
+			memset(ret, 0, size);
+			return ret;
+		}
+		free_pages((unsigned long)ret, order);
+	}
+
+	return swiotlb_alloc_buffer(hwdev, size, dma_handle, attrs);
+}
 EXPORT_SYMBOL(swiotlb_alloc_coherent);
 
 static bool swiotlb_free_buffer(struct device *dev, size_t size,
@@ -1103,6 +1107,10 @@ void *swiotlb_alloc(struct device *dev, size_t size, dma_addr_t *dma_handle,
 {
 	void *vaddr;
 
+	/* temporary workaround: */
+	if (gfp & __GFP_NOWARN)
+		attrs |= DMA_ATTR_NO_WARN;
+
 	/*
 	 * Don't print a warning when the first allocation attempt fails.
 	 * swiotlb_alloc_coherent() will print a warning when the DMA memory
@@ -1112,7 +1120,7 @@ void *swiotlb_alloc(struct device *dev, size_t size, dma_addr_t *dma_handle,
 
 	vaddr = dma_direct_alloc(dev, size, dma_handle, gfp, attrs);
 	if (!vaddr)
-		vaddr = swiotlb_alloc_coherent(dev, size, dma_handle, gfp);
+		vaddr = swiotlb_alloc_buffer(dev, size, dma_handle, attrs);
 	return vaddr;
 }