m68k: Set default dma mask for platform devices

This avoids a WARNING splat when loading the macsonic or macmace driver.
Please see commit 205e1b7f ("dma-mapping: warn when there is no
coherent_dma_mask").

This implementation of arch_setup_pdev_archdata() differs from the
powerpc one, in that this one avoids clobbering a device dma mask
which has already been initialized.

Cc: Christoph Hellwig <hch@lst.de>
Cc: Greg Ungerer <gerg@linux-m68k.org>
Signed-off-by: NFinn Thain <fthain@telegraphics.com.au>
Acked-by: NGreg Ungerer <gerg@linux-m68k.org>
Signed-off-by: NGeert Uytterhoeven <geert@linux-m68k.org>

arch/m68k/kernel/dma.c

@@ -9,6 +9,7 @@
 #include <linux/dma-mapping.h>
 #include <linux/device.h>
 #include <linux/kernel.h>
+#include <linux/platform_device.h>
 #include <linux/scatterlist.h>
 #include <linux/slab.h>
 #include <linux/vmalloc.h>
@@ -165,3 +166,12 @@ const struct dma_map_ops m68k_dma_ops = {
 	.sync_sg_for_device	= m68k_dma_sync_sg_for_device,
 };
 EXPORT_SYMBOL(m68k_dma_ops);
+
+void arch_setup_pdev_archdata(struct platform_device *pdev)
+{
+	if (pdev->dev.coherent_dma_mask == DMA_MASK_NONE &&
+	    pdev->dev.dma_mask == NULL) {
+		pdev->dev.coherent_dma_mask = DMA_BIT_MASK(32);
+		pdev->dev.dma_mask = &pdev->dev.coherent_dma_mask;
+	}
+}