mmc: sdhci: avoid sync'ing the SG if there's no misalignment

On read, we don't need to sync the whole scatterlist and then check
whether any segments need copying - if we check first, we avoid
potentially expensive cache handling.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Tested-by: Markus Pargmann <mpa@pengutronix.de>
Tested-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Chris Ball <chris@printf.net>

drivers/mmc/host/sdhci.c

@@ -602,6 +602,7 @@ static void sdhci_adma_table_post(struct sdhci_host *host,
 	u8 *align;
 	char *buffer;
 	unsigned long flags;
+	bool has_unaligned;
 
 	if (data->flags & MMC_DATA_READ)
 		direction = DMA_FROM_DEVICE;
@@ -614,7 +615,15 @@ static void sdhci_adma_table_post(struct sdhci_host *host,
 	dma_unmap_single(mmc_dev(host->mmc), host->align_addr,
 		128 * 4, direction);
 
-	if (data->flags & MMC_DATA_READ) {
+	/* Do a quick scan of the SG list for any unaligned mappings */
+	has_unaligned = false;
+	for_each_sg(data->sg, sg, host->sg_count, i)
+		if (sg_dma_address(sg) & 3) {
+			has_unaligned = true;
+			break;
+		}
+
+	if (has_unaligned && data->flags & MMC_DATA_READ) {
 		dma_sync_sg_for_cpu(mmc_dev(host->mmc), data->sg,
 			data->sg_len, direction);