lan743x driver fails to map DMA during initialization on Raspberry CM4IO

To whom it may concern,

I encountered this error when trying to get an EVB-LAN7430 evaluation
board to work with the PCIe interface on a Raspberry CM4IO board.
There was already someone on the raspberrypi/linux github who
encountered the same problem and also provided a possible fix here:
https://github.com/raspberrypi/linux/issues/4117

Please refer to the github link for a detailed error description.

The fix was tested successfully by some people who commented on the
github issue and by myself.
It seems the issue occurred on both 32 and 64 Bit builds on this system.
If I understand it correctly, this might not a universal fix.

diff --git a/drivers/net/ethernet/microchip/lan743x_main.c

b/drivers/net/ethernet/microchip/lan743x_main.c
index 8947c3a62810..96673017d6d9 100644

--- a/drivers/net/ethernet/microchip/lan743x_main.c
+++ b/drivers/net/ethernet/microchip/lan743x_main.c

@@ -2318,6 +2318,13 @@ static int lan743x_rx_ring_init(struct lan743x_rx *rx)
                ret = -EINVAL;
                goto cleanup;
        }
+
+       if (dma_set_mask_and_coherent(&rx->adapter->pdev->dev,

DMA_BIT_MASK(64))) {
+               dev_warn(&rx->adapter->pdev->dev, "lan743x_: No
suitable DMA available\n");
+               ret = -ENOMEM;
+               goto cleanup;
+       }
+
        ring_allocation_size = ALIGN(rx->ring_size *
                                     sizeof(struct lan743x_rx_descriptor),
                                     PAGE_SIZE);

--
Best regards
Andreas Hilse

On Mon, Aug 02, 2021 at 02:45:12PM +0200, Andreas Hilse wrote:

+
+       if (dma_set_mask_and_coherent(&rx->adapter->pdev->dev,
DMA_BIT_MASK(64))) {

Setting the 64-bit mask never fails, no need for the error handling
here.