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

[BOUGH CHEN]

> -----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. 

Best Regards
Haibo Chen

> 
> > 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>
> > ---
> >  drivers/mmc/mmc.c | 3 +--
> >  1 file changed, 1 insertion(+), 2 deletions(-)
> >
> > diff --git a/drivers/mmc/mmc.c b/drivers/mmc/mmc.c index
> > 1c1527cc74..55d3560b30 100644
> > --- a/drivers/mmc/mmc.c
> > +++ b/drivers/mmc/mmc.c
> > @@ -1892,8 +1892,7 @@ static int mmc_select_hs400(struct mmc *mmc)
> >  	}
> >
> >  	/* Set back to HS */
> > -	mmc_set_card_speed(mmc, MMC_HS, false);
> > -	mmc_set_clock(mmc, mmc_mode2freq(mmc, MMC_HS), false);
> > +	mmc_set_card_speed(mmc, MMC_HS, true);
> >
> >  	err = mmc_switch(mmc, EXT_CSD_CMD_SET_NORMAL,
> EXT_CSD_BUS_WIDTH,
> >  			 EXT_CSD_BUS_WIDTH_8 | EXT_CSD_DDR_FLAG);
> >
> 
> 
> --
> Best regards,
> Marek Vasut