[PATCH 4/4] mtd: spi-nor: aspeed: use command mode for reads

["Cédric Le Goater" <clg@kaod.org>]

When reading flash contents, try to use the "command mode" if the AHB
window configured for the flash module is big enough. Else, just fall
back to the "user mode" to perform the read.

Signed-off-by: Cédric Le Goater <clg@kaod.org>
---

 Changes since initial version :

 - rebased on current patchset which removed DMA support

 drivers/mtd/spi-nor/aspeed-smc.c | 27 ++++++++++++++++++++++++++-
 1 file changed, 26 insertions(+), 1 deletion(-)

diff --git a/drivers/mtd/spi-nor/aspeed-smc.c b/drivers/mtd/spi-nor/aspeed-smc.c
index 60c020482946..43015aec4557 100644
--- a/drivers/mtd/spi-nor/aspeed-smc.c
+++ b/drivers/mtd/spi-nor/aspeed-smc.c
@@ -394,6 +394,31 @@ static ssize_t aspeed_smc_read_user(struct spi_nor *nor, loff_t from,
 
 	aspeed_smc_read_from_ahb(read_buf, chip->ahb_base, len);
 	aspeed_smc_stop_user(nor);
+	return 0;
+}
+
+static ssize_t aspeed_smc_read(struct spi_nor *nor, loff_t from, size_t len,
+			       u_char *read_buf)
+{
+	struct aspeed_smc_chip *chip = nor->priv;
+
+	/*
+	 * The AHB window configured for the chip is too small for the
+	 * read offset. Use the "User mode" of the controller to
+	 * perform the read.
+	 */
+	if (from >= chip->ahb_window_size) {
+		aspeed_smc_read_user(nor, from, len, read_buf);
+		goto out;
+	}
+
+	/*
+	 * Use the "Command mode" to do a direct read from the AHB
+	 * window configured for the chip. This should be the default.
+	 */
+	memcpy_fromio(read_buf, chip->ahb_base + from, len);
+
+out:
 	return len;
 }
 
@@ -817,7 +842,7 @@ static int aspeed_smc_setup_flash(struct aspeed_smc_controller *controller,
 		nor->dev = dev;
 		nor->priv = chip;
 		spi_nor_set_flash_node(nor, child);
-		nor->read = aspeed_smc_read_user;
+		nor->read = aspeed_smc_read;
 		nor->write = aspeed_smc_write_user;
 		nor->read_reg = aspeed_smc_read_reg;
 		nor->write_reg = aspeed_smc_write_reg;
-- 
2.7.4