On Wednesday, January 4, 2017 9:24:09 AM CET Nikita Yushchenko wrote:

quoted

commit 9a57d58d116800a535510053136c6dd7a9c26e25
Author: Arnd Bergmann [off-list ref]
Date:   Tue Nov 17 14:06:55 2015 +0100

    [EXPERIMENTAL] ARM64: check implement dma_set_mask
    
    Needs work for coherent mask
    
    Signed-off-by: Arnd Bergmann [off-list ref]

Unfortunately this is far incomplete

quoted

@@ -957,6 +983,18 @@ void arch_setup_dma_ops(struct device *dev, u64 dma_base, u64 size,
 	if (!dev->archdata.dma_ops)
 		dev->archdata.dma_ops = &swiotlb_dma_ops;
 
+	/*
+	 * we don't yet support buses that have a non-zero mapping.
+	 *  Let's hope we won't need it
+	 */
+	WARN_ON(dma_base != 0);
+
+	/*
+	 * Whatever the parent bus can set. A device must not set
+	 * a DMA mask larger than this.
+	 */
+	dev->archdata.parent_dma_mask = size;
+

... because size/mask passed here for PCI devices are meaningless.

For OF platforms, this is called via of_dma_configure(), that checks
dma-ranges of node that is *parent* for host bridge. Host bridge
currently does not control this at all.

We need to think about this a bit. Is it actually the PCI host
bridge that limits the ranges here, or the bus that it is connected
to. In the latter case, the caller needs to be adapted to handle
both.

In current device trees no dma-ranges is defined for nodes that are
parents to pci host bridges. This will make of_dma_configure() to fall
back to 32-bit size for all devices on all current platforms.  Thus
applying this patch will immediately break 64-bit dma masks on all
hardware that supports it.

No, it won't break it, it will just fall back to swiotlb for all the
ones that are lacking the dma-ranges property. I think this is correct
behavior.

Also related: dma-ranges property used by several pci host bridges is
*not* compatible with "legacy" dma-ranges parsed by of_get_dma_range() -
former uses additional flags word at beginning.

Can you elaborate? Do we have PCI host bridges that use wrongly formatted
dma-ranges properties?

	Arnd