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

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Date:   Fri, 16 Oct 2020 11:45:50 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Michael Walle <michael@...le.cc>, linux-mmc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     Yangbo Lu <yangbo.lu@....com>, Ulf Hansson <ulf.hansson@...aro.org>
Subject: Re: [PATCH] mmc: sdhci-of-esdhc: set timeout to max before tuning

On 16/10/20 2:11 am, Michael Walle 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.
> 
> Signed-off-by: Michael Walle <michael@...le.cc>

Acked-by: Adrian Hunter <adrian.hunter@...el.com>

> ---
>  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 {
>