linux-kernel - Re: [PATCH v2] mmc: sdhci-of-esdhc: set timeout to max before tuning

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Date:   Fri, 23 Oct 2020 14:25:34 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Michael Walle <michael@...le.cc>
Cc:     "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Yangbo Lu <yangbo.lu@....com>,
        Adrian Hunter <adrian.hunter@...el.com>
Subject: Re: [PATCH v2] mmc: sdhci-of-esdhc: set timeout to max before tuning

On Fri, 23 Oct 2020 at 00:24, Michael Walle <michael@...le.cc> wrote:
>
> On rare occations there is the following error:
>
>   mmc0: Tuning timeout, falling back to fixed sampling clock
>
> There are SD cards which takes a significant longer time to reply to the
> first CMD19 command. The eSDHC takes the data timeout value into account
> during the tuning period. The SDHCI core doesn't explicitly set this
> timeout for the tuning procedure. Thus on the slow cards, there might be
> a spurious "Buffer Read Ready" interrupt, which in turn triggers a wrong
> sequence of events. In the end this will lead to an unsuccessful tuning
> procedure and to the above error.
>
> To workaround this, set the timeout to the maximum value (which is the
> best we can do) and the SDHCI core will take care of the proper timeout
> handling.
>
> Fixes: ba49cbd0936e ("mmc: sdhci-of-esdhc: add tuning support")
> Signed-off-by: Michael Walle <michael@...le.cc>
> Acked-by: Adrian Hunter <adrian.hunter@...el.com>

Applied for fixes and by adding a stable tag, thanks!

I am not sure for what stable kernel this applies to, but I guess we
will get notified about that, sooner or later.

Kind regards
Uffe


>
> ---
> Changes since v1:
>  - Added fixes tag. Suggested by Ulf Hansson.
>
>  drivers/mmc/host/sdhci-of-esdhc.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
>
> diff --git a/drivers/mmc/host/sdhci-of-esdhc.c b/drivers/mmc/host/sdhci-of-esdhc.c
> index 0b45eff6fed4..baf7801a1804 100644
> --- a/drivers/mmc/host/sdhci-of-esdhc.c
> +++ b/drivers/mmc/host/sdhci-of-esdhc.c
> @@ -1052,6 +1052,17 @@ static int esdhc_execute_tuning(struct mmc_host *mmc, u32 opcode)
>
>         esdhc_tuning_block_enable(host, true);
>
> +       /*
> +        * The eSDHC controller takes the data timeout value into account
> +        * during tuning. If the SD card is too slow sending the response, the
> +        * timer will expire and a "Buffer Read Ready" interrupt without data
> +        * is triggered. This leads to tuning errors.
> +        *
> +        * Just set the timeout to the maximum value because the core will
> +        * already take care of it in sdhci_send_tuning().
> +        */
> +       sdhci_writeb(host, 0xe, SDHCI_TIMEOUT_CONTROL);
> +
>         hs400_tuning = host->flags & SDHCI_HS400_TUNING;
>
>         do {
> --
> 2.20.1
>