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

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Message-ID: <CAPDyKFqrjP3-y+ucm5ybwXefsDLOYcPF9XqMciwhRkjD5NXLBg@mail.gmail.com>
Date:	Thu, 8 Oct 2015 12:59:12 +0200
From:	Ulf Hansson <ulf.hansson@...aro.org>
To:	Chaotian Jing <chaotian.jing@...iatek.com>
Cc:	Matthias Brugger <matthias.bgg@...il.com>,
	Jaehoon Chung <jh80.chung@...sung.com>,
	Adrian Hunter <adrian.hunter@...el.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 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.

>                 mmc_host_clk_release(host);
>                 return -ENOSYS;
>         }
> --
> 1.8.1.1.dirty
>

Kind regards
Uffe
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