mmc: Avoid redundant switching to 1-bit bus width for MMC cards

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.

panto: Minor cosmetic edit removing superfluous parentheses.

Signed-off-by: Andrew Gabbasov <andrew_gabbasov@mentor.com>
Tested-by: Alexey Brodkin <abrodkin@synopsys.com>
Signed-off-by: Pantelis Antoniou <pantelis.antoniou@konsulko.com>

diff --git a/drivers/mmc/mmc.c b/drivers/mmc/mmc.c
index 19ac4c4..bdd7894 100644 (file)
--- a/drivers/mmc/mmc.c
+++ b/drivers/mmc/mmc.c
@@ -1381,6 +1381,18 @@ 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
                         */