of_dma_configure() was *supposed* to be following the same logic as
acpi_dma_configure() and only setting bus_dma_mask if some range was
specified by the firmware. However, it seems that subtlety got lost in
the process of fitting it into the differently-shaped control flow, and
as a result the force_dma==true case ends up always setting the bus mask
to the 32-bit default, which is not what anyone wants.

Make sure we only touch it if the DT actually said so.

Fixes: 6c2fb2ea7636 ("of/device: Set bus DMA mask as appropriate")
Reported-by: Aaro Koskinen <[email protected]>
Reported-by: Jean-Philippe Brucker <[email protected]>
Tested-by: Aaro Koskinen <[email protected]>
Tested-by: John Stultz <[email protected]>
Tested-by: Geert Uytterhoeven <[email protected]>
Tested-by: Robert Richter <[email protected]>
Signed-off-by: Robin Murphy <[email protected]>
---

 v2: Add comment, collect tested-by tags

 drivers/of/device.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/of/device.c b/drivers/of/device.c
index 0f27fad9fe94..5592437bb3d1 100644
--- a/drivers/of/device.c
+++ b/drivers/of/device.c
@@ -149,9 +149,11 @@ int of_dma_configure(struct device *dev, struct 
device_node *np, bool force_dma)
         * set by the driver.
         */
        mask = DMA_BIT_MASK(ilog2(dma_addr + size - 1) + 1);
-       dev->bus_dma_mask = mask;
        dev->coherent_dma_mask &= mask;
        *dev->dma_mask &= mask;
+       /* ...but only set bus mask if we found valid dma-ranges earlier */
+       if (!ret)
+               dev->bus_dma_mask = mask;
 
        coherent = of_dma_is_coherent(np);
        dev_dbg(dev, "device is%sdma coherent\n",
-- 
2.19.1.dirty

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