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

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

在 2015/9/6 20:09, Yousong Zhou 写道:
> Hi,
>
> On 6 September 2015 at 08:12, Shawn Lin <shawn.lin-TNX95d0MmH7DzftRWevZcw@public.gmane.org> wrote:
>> 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.
>>
>
> Maybe the fix is anti-spec.  But the fact is that the card works on
> many other platforms with the builtin card reader (not through an USB
> adapter), including Mac OS X, my old Nokia Symbian phone, and Windows.
>
>>> 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.
>>
>
> The SD Specification (simplified version) says "If CRC error occurs on
> the status data, the host should issue a power cycle.", so I guess the
> above approach is anti-spec in some way :)
>

Right，I was guessing that way from your intention.

> In case it may help debug this problem, I'd like to add that the card
> previously worked fine with U-Boot before commit [1].  This can also
> be confirmed by Debian Jessie installer image with which the old
> U-Boot there worked fine while the kernel (3.16) did not.
>
>   [1] sunxi: mmc: Properly setup mod-clk and clock sampling phases,
> http://git.denx.de/?p=u-boot.git;a=commit;h=fc3a832576ce7bb597b1823935bfb7dcca235c3c
>

Interesting... but that at least prove your patch is a workaround but 
not find the root cause.

Anyway, look into commit-sha [1], can you have a test by restoring 
mod-clk and clock sampling phases before jump to kernel.

I happended to fix some problems which seems *similar* to yours(but I'm 
not sure just from commit[1]'s msg):

https://patchwork.kernel.org/patch/7119661/

> Cheers
>
>                  yousong
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>


-- 
Best Regards
Shawn Lin

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