mmc: sdhci: avoid walking SG list for writes

If we are writing data to the card, there is no point in walking the
scatterlist to find out if there are any unaligned entries; this is a
needless waste of CPU cycles.  Avoid this by checking for a non-read
tranfer first.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Tested-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/host/sdhci.c

@@ -559,37 +559,39 @@ static void sdhci_adma_table_post(struct sdhci_host *host,
 	void *align;
 	char *buffer;
 	unsigned long flags;
-	bool has_unaligned;
 
 	if (data->flags & MMC_DATA_READ)
 		direction = DMA_FROM_DEVICE;
 	else
 		direction = DMA_TO_DEVICE;
 
-	/* 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) & SDHCI_ADMA2_MASK) {
-			has_unaligned = true;
-			break;
-		}
+	if (data->flags & MMC_DATA_READ) {
+		bool has_unaligned = false;
 
-	if (has_unaligned && data->flags & MMC_DATA_READ) {
-		dma_sync_sg_for_cpu(mmc_dev(host->mmc), data->sg,
-			data->sg_len, direction);
+		/* Do a quick scan of the SG list for any unaligned mappings */
+		for_each_sg(data->sg, sg, host->sg_count, i)
+			if (sg_dma_address(sg) & SDHCI_ADMA2_MASK) {
+				has_unaligned = true;
+				break;
+			}
 
-		align = host->align_buffer;
+		if (has_unaligned) {
+			dma_sync_sg_for_cpu(mmc_dev(host->mmc), data->sg,
+				data->sg_len, direction);
 
-		for_each_sg(data->sg, sg, host->sg_count, i) {
-			if (sg_dma_address(sg) & SDHCI_ADMA2_MASK) {
-				size = SDHCI_ADMA2_ALIGN -
-				       (sg_dma_address(sg) & SDHCI_ADMA2_MASK);
+			align = host->align_buffer;
 
-				buffer = sdhci_kmap_atomic(sg, &flags);
-				memcpy(buffer, align, size);
-				sdhci_kunmap_atomic(buffer, &flags);
+			for_each_sg(data->sg, sg, host->sg_count, i) {
+				if (sg_dma_address(sg) & SDHCI_ADMA2_MASK) {
+					size = SDHCI_ADMA2_ALIGN -
+					       (sg_dma_address(sg) & SDHCI_ADMA2_MASK);
 
-				align += SDHCI_ADMA2_ALIGN;
+					buffer = sdhci_kmap_atomic(sg, &flags);
+					memcpy(buffer, align, size);
+					sdhci_kunmap_atomic(buffer, &flags);
+
+					align += SDHCI_ADMA2_ALIGN;
+				}
 			}
 		}
 	}