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

[Tom Rini]

On Mon, Mar 25, 2019 at 12:16:53PM +0100, Marek Vasut wrote:
> On 3/25/19 11:24 AM, BOUGH CHEN wrote:
> > 
> >> -----Original Message-----
> >> From: Marek Vasut [mailto:marek.vasut at gmail.com]
> >> Sent: 2019年3月18日 19:53
> >> To: BOUGH CHEN <haibo.chen at nxp.com>; jh80.chung at samsung.com;
> >> trini at konsulko.com
> >> Cc: marek.vasut+renesas at gmail.com; Ye Li <ye.li at nxp.com>; dl-uboot-imx
> >> <uboot-imx at nxp.com>; u-boot at lists.denx.de
> >> Subject: Re: [PATCH] mmc: correct the HS400 initialization process
> >>
> >> On 3/18/19 9:23 AM, 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, make sure in the function
> >>> mmc_set_card_speed(), after switch to HS mode, first config the clock
> >>> rate, then read the EXT_CSD. Otherwise read EXT_CSD in HS mode at
> >>> wrong clock rate, e.g. 200MHz, may lead to uncertain result.
> >>
> >> I think the fix is right, but the reasoning for it is not.
> >>
> >> If you call mmc_set_card_speed() with hsdowngrade=true, it will result in
> >> calling __mmc_switch() with send_status=false , which in turn means that
> >> after issuing the MMC_CMD_SWITCH command, the code won't poll the card
> >> using MMC_CMD_SEND_STATUS, but just wait a bit and then switch the bus
> >> properties. This is indeed required when switching bus properties.
> >> And that's what I think was making your card unstable.
> >>
> >> Is that the case ?
> > 
> > Sorry for the tardy reply, I miss the email last week.
> > No, if without this patch, even I add the dealy after the switch command, eMMC still stuck after the CMD8.
> > The main issue is that, in mmc_set_card_speed, if the bus mode the HS mode, it will send CMD8 to get the EXT_CSD, but the clock is still 200MHz at that time.
> > It is wrong that EMMC output data in HS mode at 200MHz. 
> 
> OK, that makes sense.

Do we need a re-worded commit message then or no?  Thanks!

-- 
Tom
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