char: xillybus: Allow 64-bit DMA on PCIe interface

Until now, only 32-bit DMA addressing was allowed, following a report on
some old Intel machine that dropped 64-bit PCIe packets, even though
pci_set_dma_mask() was successful with DMA_BIT_MASK(64).

But then came TI's Keystone II chip (ARM Cortex A15 + DSPs), which refuses
32-bit DMA addressing (for good reasons). So 64-bit DMA is allowed as a
fallback option.

Signed-off-by: Eli Billauer <eli.billauer@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/char/xillybus/xillybus_pcie.c b/drivers/char/xillybus/xillybus_pcie.c
index d8266bc2ae356138a70672b081a1e20b23594e2c..9418300214e985472fbd76f1c3e5cd1d1c186a2a 100644 (file)
--- a/drivers/char/xillybus/xillybus_pcie.c
+++ b/drivers/char/xillybus/xillybus_pcie.c
@@ -193,14 +193,16 @@ static int xilly_probe(struct pci_dev *pdev,
        }
 
        /*
-        * In theory, an attempt to set the DMA mask to 64 and dma_using_dac=1
-        * is the right thing. But some unclever PCIe drivers report it's OK
-        * when the hardware drops those 64-bit PCIe packets. So trust
-        * nobody and use 32 bits DMA addressing in any case.
+        * Some (old and buggy?) hardware drops 64-bit addressed PCIe packets,
+        * even when the PCIe driver claims that a 64-bit mask is OK. On the
+        * other hand, on some architectures, 64-bit addressing is mandatory.
+        * So go for the 64-bit mask only when failing is the other option.
         */
 
        if (!pci_set_dma_mask(pdev, DMA_BIT_MASK(32))) {
                endpoint->dma_using_dac = 0;
+       } else if (!pci_set_dma_mask(pdev, DMA_BIT_MASK(64))) {
+               endpoint->dma_using_dac = 1;
        } else {
                dev_err(endpoint->dev, "Failed to set DMA mask. Aborting.\n");
                return -ENODEV;