linux-kernel - Re: [PATCH v2 2/2] mmc: core: fall back host->f_init if failing to init mmc card after resume

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Date:	Tue, 02 Aug 2016 19:47:32 +0900
From:	Jaehoon Chung <jh80.chung@...sung.com>
To:	Shawn Lin <shawn.lin@...k-chips.com>,
	Ulf Hansson <ulf.hansson@...aro.org>
Cc:	Adrian Hunter <adrian.hunter@...el.com>, linux-mmc@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Doug Anderson <dianders@...omium.org>,
	linux-rockchip@...ts.infradead.org
Subject: Re: [PATCH v2 2/2] mmc: core: fall back host->f_init if failing to
 init mmc card after resume

Hi Shawn,

On 08/02/2016 06:07 PM, Shawn Lin wrote:
> Hi Ulf,
> 
> 在 2016/7/20 9:57, Shawn Lin 写道:
>> We observed the failure of initializing card after resume
>> accidentally. It's hard to reproduce but we did get report from
>> the suspend/resume test of our RK3399 mp test farm . Unfortunately,
>> we still fail to figure out what was going wrong at that time.
>> Also we can't achieve it by retrying the host->f_init without falling
>> back it. But this patch will solve the problem as we could add some log
>> there and see that we resume the mmc card successfully after falling
>> back the host->f_init. There is no obvious side effect found, so it seems
>> this patch will improve the stability.
>>
>> [   93.405085] mmc1: unexpected status 0x800900 after switch
>> [   93.408474] mmc1: switch to bus width 1 failed
>> [   93.408482] mmc1: mmc_select_hs200 failed, error -110
>> [   93.408492] mmc1: error -110 during resume (card was removed?)
>> [   93.408705] PM: resume of devices complete after 213.453 msecs
>>

Status 0x800900 is COM_CRC_ERROR..it seems that CRC check fails.
But i don't know what is related with "fall back host->f_init".

I don't have a knowledge of rockchip...
but in my experience, there are some cases, not mmc core problem..

1. Exynos is using the gpio as clk/cmd/data line..and gpio has the driver strength value.
If driver strength is changed after resuming, it's possible to occur the error.

2. And glitch for I/O line..this loop has the delay..Just delay? 

So you can check the other problem... :)

At Booting time, f_init can use 400K..but after resuming..f_init need to use 100K..hmm..strange..

Best Regards,
Jaehoon Chung

> 
> Any comments for this patch? :)
> 
>> Signed-off-by: Shawn Lin <shawn.lin@...k-chips.com>
>>
>> ---
>>
>> Changes in v2:
>> - remove mmc_power_off
>> - take f_min into consideration
>>
>>  drivers/mmc/core/mmc.c | 19 +++++++++++++++++--
>>  1 file changed, 17 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
>> index 403b97b..a2891c1 100644
>> --- a/drivers/mmc/core/mmc.c
>> +++ b/drivers/mmc/core/mmc.c
>> @@ -1945,6 +1945,7 @@ static int mmc_suspend(struct mmc_host *host)
>>  static int _mmc_resume(struct mmc_host *host)
>>  {
>>      int err = 0;
>> +    int i;
>>
>>      BUG_ON(!host);
>>      BUG_ON(!host->card);
>> @@ -1954,8 +1955,22 @@ static int _mmc_resume(struct mmc_host *host)
>>      if (!mmc_card_suspended(host->card))
>>          goto out;
>>
>> -    mmc_power_up(host, host->card->ocr);
>> -    err = mmc_init_card(host, host->card->ocr, host->card);
>> +    /*
>> +     * Let's try to fallback the host->f_init
>> +     * if failing to init mmc card after resume.
>> +     */
>> +    for (i = 0; i < ARRAY_SIZE(freqs); i++) {
>> +        if (host->f_init < max(freqs[i], host->f_min))
>> +            continue;
>> +        else
>> +            host->f_init = max(freqs[i], host->f_min);
>> +
>> +        mmc_power_up(host, host->card->ocr);
>> +        err = mmc_init_card(host, host->card->ocr, host->card);
>> +        if (!err)
>> +            break;
>> +    }
>> +
>>      mmc_card_clr_suspended(host->card);
>>
>>  out:
>>
> 
>