dmaengine: rcar-dmac: Add dma-channel-mask property support

This patch adds dma-channel-mask property support not to reserve
some DMA channels for some reasons. (for example: a heterogeneous
CPU uses it.)
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/1568010892-17606-5-git-send-email-yoshihiro.shimoda.uh@renesas.comSigned-off-by: Vinod Koul <vkoul@kernel.org>

drivers/dma/sh/rcar-dmac.c

@@ -203,7 +203,7 @@ struct rcar_dmac {
 
 	unsigned int n_channels;
 	struct rcar_dmac_chan *channels;
-	unsigned int channels_mask;
+	u32 channels_mask;
 
 	DECLARE_BITMAP(modules, 256);
 };
@@ -1810,7 +1810,15 @@ static int rcar_dmac_parse_of(struct device *dev, struct rcar_dmac *dmac)
 		return -EINVAL;
 	}
 
+	/*
+	 * If the driver is unable to read dma-channel-mask property,
+	 * the driver assumes that it can use all channels.
+	 */
 	dmac->channels_mask = GENMASK(dmac->n_channels - 1, 0);
+	of_property_read_u32(np, "dma-channel-mask", &dmac->channels_mask);
+
+	/* If the property has out-of-channel mask, this driver clears it */
+	dmac->channels_mask &= GENMASK(dmac->n_channels - 1, 0);
 
 	return 0;
 }