linux-kernel - Re: [PATCH v2] mmc: core: Fix init

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Date:	Thu, 8 Oct 2015 15:35:44 +0200
From:	Ulf Hansson <ulf.hansson@...aro.org>
To:	Adrian Hunter <adrian.hunter@...el.com>
Cc:	Chaotian Jing <chaotian.jing@...iatek.com>,
	Matthias Brugger <matthias.bgg@...il.com>,
	Jaehoon Chung <jh80.chung@...sung.com>,
	Fabio Estevam <fabio.estevam@...escale.com>,
	Johan Rudholm <johan.rudholm@...s.com>,
	Gwendal Grignou <gwendal@...omium.org>,
	linux-mmc <linux-mmc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	linux-mediatek@...ts.infradead.org,
	srv_heupstream <srv_heupstream@...iatek.com>,
	Sascha Hauer <kernel@...gutronix.de>
Subject: Re: [PATCH v2] mmc: core: Fix init_card in 52Mhz

On 8 October 2015 at 15:03, Adrian Hunter <adrian.hunter@...el.com> wrote:
> On 08/10/15 13:59, Ulf Hansson wrote:
>> On 8 October 2015 at 09:09, Chaotian Jing <chaotian.jing@...iatek.com> wrote:
>>> Suppose that we got a data crc error, and it triggers the mmc_reset.
>>> mmc_reset will call mmc_send_status to see if HW reset was supported.
>>> before issue CMD13, it will do retune, and if EMMC was in HS400 mode,
>>> it will reduce frequency to 52Mhz firstly, then results in card init
>>> was doing at 52Mhz.
>>> The mmc_send_status was originally only done for mmc_test, so if retune
>>> needed, do not call mmc_send_status.
>>>
>>> Signed-off-by: Chaotian Jing <chaotian.jing@...iatek.com>
>>> Suggested-by: Adrian Hunter <adrian.hunter@...el.com>
>>> ---
>>>  drivers/mmc/card/mmc_test.c | 6 ++++++
>>>  drivers/mmc/core/mmc.c      | 2 +-
>>>  2 files changed, 7 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/mmc/card/mmc_test.c b/drivers/mmc/card/mmc_test.c
>>> index b78cf5d..2f78bfb 100644
>>> --- a/drivers/mmc/card/mmc_test.c
>>> +++ b/drivers/mmc/card/mmc_test.c
>>> @@ -2272,6 +2272,12 @@ static int mmc_test_hw_reset(struct mmc_test_card *test)
>>>         if (!mmc_card_mmc(card) || !mmc_can_reset(card))
>>>                 return RESULT_UNSUP_CARD;
>>>
>>> +       if (host->need_retune) {
>>> +               pr_info("%s: cannot test hw reset because retune needed\n",
>>> +                       mmc_hostname(test->card->host));
>>> +               return RESULT_FAIL;
>>> +       }
>>> +
>>>         err = mmc_hw_reset(host);
>>>         if (!err)
>>>                 return RESULT_OK;
>>> diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
>>> index e726903..647c96d 100644
>>> --- a/drivers/mmc/core/mmc.c
>>> +++ b/drivers/mmc/core/mmc.c
>>> @@ -1938,7 +1938,7 @@ static int mmc_reset(struct mmc_host *host)
>>>         host->ops->hw_reset(host);
>>>
>>>         /* If the reset has happened, then a status command will fail */
>>> -       if (!mmc_send_status(card, &status)) {
>>> +       if (!host->need_retune && !mmc_send_status(card, &status)) {
>>
>> No, this seem like the wrong solution! The main purpose of mmc_reset()
>> is to try to reset and re-initiate the card, to make it operational
>> again.
>>
>> I can't find a good reason to why we want to do a mmc_send_status() at
>> this point, as even if it succeeds it will only tell us that the card
>> has not been "hw-reset". No matter what, we should still try to make
>> it fully operational again and thus give mmc_init_card() a try.
>>
>>>>From this reasoning, I suggest we remove the call to mmc_send_status()
>> from this path, as that will also address your issue with CRC errors
>> in combination with re-tune.
>
> Then you need to remove the hw_reset test from mmc_test.  Refer:
>
>         http://marc.info/?l=linux-mmc&m=144360165906544&w=2
>

I realize that the test becomes a bit different, but I don't think it's useless.

If we add a check for MMC_CAP_HW_RESET and verify that the
host->ops->hw_reset exists, then we can assume that the "hw_reset"
sequence has executed. And if mmc_init_card() fails, that would
probably mean that the reset also failed, right?

Kind regards
Uffe
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