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

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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>
This commit is contained in:
Andrew Gabbasov 2014-12-25 10:22:24 -06:00 committed by Pantelis Antoniou
parent 9e41a00b57
commit bf4770731c
1 changed files with 12 additions and 0 deletions
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12
drivers/mmc/mmc.c
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@ -1380,6 +1380,18 @@ static int mmc_startup(struct mmc *mmc)
unsigned int extw = ext_csd_bits[idx];
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