[U-Boot] [U-Boot, v2] mmc: correct the HS400 initialization process

[Tom Rini]

On Tue, Mar 26, 2019 at 06:24:17AM +0000, BOUGH CHEN wrote:

> After the commit b9a2a0e2e9c0 ("mmc: Add support for downgrading
> HS200/HS400 to HS mode"), it add a parameter in mmc_set_card_speed()
> which indicates that the HS200/HS400 to HS downgrade is happening.
> 
> During the HS400 initialization, first select to HS200, and config
> the related clock rate, then downgrade to HS mode. So here also need
> to config the downgrade value to be true for two reasons. First,
> make sure in the function mmc_set_card_speed(), after switch to HS
> mode, first config the clock rate, then read the EXT_CSD, avoid
> receiving data of EXT_CSD in HS mode at 200MHz. Second, after issue
> the MMC_CMD_SWITCH command, it need to wait a bit then switch bus
> properties.
> 
> Test on i.MX8QM MEK board, some Micron eMMC will stuck in transfer
> mode in this case, and USDHC will never get data transfer complete
> status, cause the uboot hang.
> 
> Signed-off-by: Haibo Chen <haibo.chen at nxp.com>
> Acked-by: Marek Vasut <marek.vasut at gmail.com>

Applied to u-boot/master, thanks!

-- 
Tom
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