[PATCH 4/4] arm/imx: fix imx6q mmc error when mounting rootfs

The following error is seen in some case when mounting rootfs from
SD/MMC cards.

?Waiting for root device /dev/mmcblk0p1...
?mmc1: host does not support reading read-only switch. assuming write-enable.
?mmc1: new high speed SDHC card at address b368
?mmcblk0: mmc1:b368 SDC ? 3.74 GiB
? mmcblk0: p1
?mmc1: Timeout waiting for hardware interrupt.
?mmcblk0: error -110 transferring data, sector 3678224, nr 40, cmd response 0x900, card status 0xc00
?end_request: I/O error, dev mmcblk0, sector 3678225
?Buffer I/O error on device mmcblk0p1, logical block 458754
?lost page write due to I/O error on mmcblk0p1

This patch fixes the problem by lowering the usdhc clock and correcting
watermark configuration.

Signed-off-by: Shawn Guo <redacted>
Cc: Chris Ball <redacted>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
---
?arch/arm/mach-imx/clock-imx6q.c ? ?| ? 17 ++++++++++++++++-
?drivers/mmc/host/sdhci-esdhc-imx.c | ? ?8 ++++++++
?2 files changed, 24 insertions(+), 1 deletions(-)

diff --git a/arch/arm/mach-imx/clock-imx6q.c b/arch/arm/mach-imx/clock-imx6q.c
index e0b926d..613a1b9 100644
--- a/arch/arm/mach-imx/clock-imx6q.c
+++ b/arch/arm/mach-imx/clock-imx6q.c

@@ -1139,7 +1139,7 @@ static int _clk_set_rate(struct clk *clk, unsigned long rate)

? ? ? ? ? ? ? ?return -EINVAL;

? ? ? ?max_div = ((d->bm_pred >> d->bp_pred) + 1) *
- ? ? ? ? ? ? ? ? ((d->bm_pred >> d->bp_pred) + 1);
+ ? ? ? ? ? ? ? ? ((d->bm_podf >> d->bp_podf) + 1);

? ? ? ?div = parent_rate / rate;
? ? ? ?if (div == 0)

@@ -2002,6 +2002,21 @@ int __init mx6q_clocks_init(void)

? ? ? ?clk_set_rate(&asrc_serial_clk, 1500000);
? ? ? ?clk_set_rate(&enfc_clk, 11000000);

+ ? ? ? /*
+ ? ? ? ?* Before pinctrl API is available, we have to rely on the pad
+ ? ? ? ?* configuration set up by bootloader. ?For usdhc example here,
+ ? ? ? ?* u-boot sets up the pads for 49.5 MHz case, and we have to lower
+ ? ? ? ?* the usdhc clock from 198 to 49.5 MHz to match the pad configuration.