Re: Re: [RFC] mmc: core: Set clock before switching to highspeed mode.

[Shawn Lin <shawn.lin-TNX95d0MmH7DzftRWevZcw@public.gmane.org>]

On 2015/9/5 22:58, Hans de Goede wrote:
> Hi Shawn Lin,
>
> On 05-09-15 16:07, Shawn Lin wrote:
>> On 2015/9/5 18:19, Yousong Zhou wrote:
>>> A SD card with sunxi-mmc can fail with the following error message
>>> (RCD for
>>> response CRC error) when trying to switch to highspeed mode.  Setting
>>> the bus
>>> clock before the access mode switch fixed it.
>>
>> No, that's wrong!
>>
>> Before this card is switched to highspeed, it works under
>> identification mode(From spec: bus clock <= 400KHz). How could you
>> raise bus clock to higher clk rate which I _guess_ is 52MHz before you
>> notify sd cards to run into highspeed mode?
>>
>> Althought it works for this card, this patch will not please the other
>> cards that they might not reply CMDs any longer including the
>> following CMD6.
>
> Thanks for the feedback, this is exactly why I asked Yousong Zhou to
> take this
> to the mmc list.
>
> So if this is not the proper fix for the problem that Yousong Zhou is
> seeing, then
> what might be the proper fix ?
>

 From my knowledge of mmc, there hadn't have a way to deal with this 
"broken" case. In another word, IMO,it's ANTI-SPEC. We can't be too spec 
sometimes, but at least we shouldn't violate it.

> Could it be that the sunxi-mmc is doing some things in the wrong order when
> changing the clock, or is this all under control of the mmc core ?
>

all of this is under control of the mmc core.
So if Yongsong does want this card to work for any linux-based mmc 
stack, I guess something like that should be "better"?

if (switch to HS fail) {
	set_bus_clk
	goto retry switch to HS
}

BUT...I admit it seems strange as well.


> Regards,
>
> Hans
>
>
>>
>>
>>>
>>>      [    1.112060] mmc0: host does not support reading read-only
>>> switch, assuming write-enable
>>>      [    1.120203] ehci-platform 1c1c000.usb: irq 31, io mem 0x01c1c000
>>>      [    1.126527] sunxi-mmc 1c0f000.mmc: smc 0 err, cmd 6, RD RCE !!
>>>      [    1.132388] sunxi-mmc 1c0f000.mmc: data error, sending stop
>>> command
>>>      [    1.139451] sunxi-mmc 1c0f000.mmc: send stop command failed
>>>      [    1.145056] mmc0: error -110 whilst initialising SD card
>>>      [    1.150424] ehci-platform 1c1c000.usb: USB 2.0 started, EHCI
>>> 1.00
>>>      [    1.156533] sunxi-mmc 1c0f000.mmc: smc 0 err, cmd 1, RTO !!
>>>
>>> Signed-off-by: Yousong Zhou <yszhou4tech-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
>>> ---
>>>   drivers/mmc/core/sd.c |   10 +++++-----
>>>   1 file changed, 5 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/drivers/mmc/core/sd.c b/drivers/mmc/core/sd.c
>>> index 4e7366a..402a8db 100644
>>> --- a/drivers/mmc/core/sd.c
>>> +++ b/drivers/mmc/core/sd.c
>>> @@ -366,6 +366,11 @@ int mmc_sd_switch_hs(struct mmc_card *card)
>>>           return -ENOMEM;
>>>       }
>>>
>>> +    /*
>>> +     * Set bus frequency to match highspeed mode.
>>> +     */
>>> +    mmc_set_clock(card->host, mmc_sd_get_max_clock(card));
>>> +
>>>       err = mmc_sd_switch(card, 1, 0, 1, status);
>>>       if (err)
>>>           goto out;
>>> @@ -969,11 +974,6 @@ static int mmc_sd_init_card(struct mmc_host
>>> *host, u32 ocr,
>>>               goto free_card;
>>>
>>>           /*
>>> -         * Set bus speed.
>>> -         */
>>> -        mmc_set_clock(host, mmc_sd_get_max_clock(card));
>>> -
>>> -        /*
>>>            * Switch to wider bus (if supported).
>>>            */
>>>           if ((host->caps & MMC_CAP_4_BIT_DATA) &&
>>>
>>
>>
>
>
>


-- 
Best Regards
Shawn Lin