[U-Boot] [PATCH 1/2] mmc: Avoid redundant switching to 1-bit bus width for MMC cards

[Andrew Gabbasov]

If all the commands switching an MMC card to 4- or 8-bit bus width fail,
and the bus width for the controller and the driver is still set
to default 1 bit, there is no need to send one more command to switch
the card to 1-bit bus width. Also, if the card or host controller do not
support wider bus widths, there is no need to send a switch command at all.

However, if one of switch commands succeeds, but the subsequent ext_csd
fields comparison fails, the card should be switched to some other bus width
(next in the list for the loop), or to default 1-bit bus width as a last
resort. That's why it would be incorrect to just remove the 1-bit bus width
case from the list, it should still be processed in some cases.

Signed-off-by: Andrew Gabbasov <andrew_gabbasov at mentor.com>
Tested-by: Alexey Brodkin <abrodkin at synopsys.com>
---
 drivers/mmc/mmc.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/mmc/mmc.c b/drivers/mmc/mmc.c
index 1eb9c27..c0cf318 100644
--- a/drivers/mmc/mmc.c
+++ b/drivers/mmc/mmc.c
@@ -1139,6 +1139,18 @@ static int mmc_startup(struct mmc *mmc)
 			unsigned int caps = ext_to_hostcaps[extw];
 
 			/*
+			 * If the bus width is still not changed,
+			 * don't try to set the default again.
+			 * Otherwise, recover from switch attempts
+			 * by switching to 1-bit bus width.
+			 */
+			if ((extw == EXT_CSD_BUS_WIDTH_1) &&
+			    (mmc->bus_width == 1)) {
+				err = 0;
+				break;
+			}
+
+			/*
 			 * Check to make sure the card and controller support
 			 * these capabilities
 			 */
-- 
2.1.0