mmc: meson-gx: check for scatterlist size alignment in block mode

Enable SGDMA support for SD_IO_RW_EXTENDED and add proper check
for scatterlist size alignment in block mode.

According to documentation, in SDIO block mode meson-gx DMA could
only handle buffers with sizes that are multiples of SDIO block size.

Some SDIO drivers like brcmfmac use scatterlist API, but do not enforce
proper scatterlist buffer size alignemnt, this looks like a root cause
of non-working CMD53.

Some minor style fixes.

Signed-off-by: Dmitry Lebed <lebed.dmitry@gmail.com>
Reviewed-by: Jerome Brunet <jbrunet@baylibre.com>
Link: https://lore.kernel.org/r/20201218075312.67338-1-lebed.dmitry@gmail.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/host/meson-gx-mmc.c

@@ -227,7 +227,6 @@ static void meson_mmc_get_transfer_mode(struct mmc_host *mmc,
 	struct mmc_data *data = mrq->data;
 	struct scatterlist *sg;
 	int i;
-	bool use_desc_chain_mode = true;
 
 	/*
 	 * When Controller DMA cannot directly access DDR memory, disable
@@ -237,25 +236,33 @@ static void meson_mmc_get_transfer_mode(struct mmc_host *mmc,
 	if (host->dram_access_quirk)
 		return;
 
-	/*
-	 * Broken SDIO with AP6255-based WiFi on Khadas VIM Pro has been
-	 * reported. For some strange reason this occurs in descriptor
-	 * chain mode only. So let's fall back to bounce buffer mode
-	 * for command SD_IO_RW_EXTENDED.
-	 */
-	if (mrq->cmd->opcode == SD_IO_RW_EXTENDED)
-		return;
+	if (data->blocks > 1) {
+		/*
+		 * In block mode DMA descriptor format, "length" field indicates
+		 * number of blocks and there is no way to pass DMA size that
+		 * is not multiple of SDIO block size, making it impossible to
+		 * tie more than one memory buffer with single SDIO block.
+		 * Block mode sg buffer size should be aligned with SDIO block
+		 * size, otherwise chain mode could not be used.
+		 */
+		for_each_sg(data->sg, sg, data->sg_len, i) {
+			if (sg->length % data->blksz) {
+				WARN_ONCE(1, "unaligned sg len %u blksize %u\n",
+					  sg->length, data->blksz);
+				return;
+			}
+		}
+	}
 
-	for_each_sg(data->sg, sg, data->sg_len, i)
+	for_each_sg(data->sg, sg, data->sg_len, i) {
 		/* check for 8 byte alignment */
-		if (sg->offset & 7) {
+		if (sg->offset % 8) {
 			WARN_ONCE(1, "unaligned scatterlist buffer\n");
-			use_desc_chain_mode = false;
-			break;
+			return;
 		}
+	}
 
-	if (use_desc_chain_mode)
-		data->host_cookie |= SD_EMMC_DESC_CHAIN_MODE;
+	data->host_cookie |= SD_EMMC_DESC_CHAIN_MODE;
 }
 
 static inline bool meson_mmc_desc_chain_mode(const struct mmc_data *data)