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

[Marek Vasut]

On 3/25/19 1:10 PM, Tom Rini wrote:
> 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!

A bit wouldn't hurt, to clarify things.

-- 
Best regards,
Marek Vasut