MMC: OMAP: fix broken MMC on OMAP15XX/OMAP5910/OMAP310

MMC: OMAP: fix broken MMC on OMAP15XX/OMAP5910/OMAP310

commit e8cde625bfe8a714a856e1366bcbb259d7346095 upstream.

Since v2.6.22 or so there has been reports [1] about OMAP MMC being
broken on OMAP15XX based hardware (OMAP5910 and OMAP310). The breakage
seems to have been caused by commit 46a6730e3ff9 ("mmc-omap: Fix
omap to use MMC_POWER_ON") that changed clock enabling to be done
on MMC_POWER_ON. This can happen multiple times in a row, and on 15XX
the hardware doesn't seem to like it and the MMC just stops responding.
Fix by memorizing the power mode and do the init only when necessary.

Before the patch (on Palm TE):

	mmc0: new SD card at address b368
	mmcblk0: mmc0:b368 SDC   977 MiB
	mmci-omap mmci-omap.0: command timeout (CMD18)
	mmci-omap mmci-omap.0: command timeout (CMD13)
	mmci-omap mmci-omap.0: command timeout (CMD13)
	mmci-omap mmci-omap.0: command timeout (CMD12) [x 6]
	mmci-omap mmci-omap.0: command timeout (CMD13) [x 6]
	mmcblk0: error -110 requesting status
	mmci-omap mmci-omap.0: command timeout (CMD8)
	mmci-omap mmci-omap.0: command timeout (CMD18)
	mmci-omap mmci-omap.0: command timeout (CMD13)
	mmci-omap mmci-omap.0: command timeout (CMD13)
	mmci-omap mmci-omap.0: command timeout (CMD12) [x 6]
	mmci-omap mmci-omap.0: command timeout (CMD13) [x 6]
	mmcblk0: error -110 requesting status
	mmcblk0: recovery failed!
	print_req_error: I/O error, dev mmcblk0, sector 0
	Buffer I/O error on dev mmcblk0, logical block 0, async page read
	 mmcblk0: unable to read partition table

After the patch:

	mmc0: new SD card at address b368
	mmcblk0: mmc0:b368 SDC   977 MiB
	 mmcblk0: p1

The patch is based on a fix and analysis done by Ladislav Michl.

Tested on OMAP15XX/OMAP310 (Palm TE), OMAP1710 (Nokia 770)
and OMAP2420 (Nokia N810).

[1] https://marc.info/?t=123175197000003&r=1&w=2

Fixes: 46a6730e3ff9 ("mmc-omap: Fix omap to use MMC_POWER_ON")
Reported-by: Ladislav Michl <ladis@linux-mips.org>
Reported-by: Andrzej Zaborowski <balrogg@gmail.com>
Tested-by: Ladislav Michl <ladis@linux-mips.org>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Cc: stable@vger.kernel.org
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>