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Subject: Re: [PATCH] sdhci: fix the fake timeout bug
To:     "Du, Alek" <alek.du@intel.com>, linux-mmc@vger.kernel.org,
        ulf.hansson@linaro.org
Cc:     linux-kernel@vger.kernel.org
References: <20181130150028.732896d8@xdu1-mobl>
From:   Adrian Hunter <adrian.hunter@intel.com>
Organization: Intel Finland Oy, Registered Address: PL 281, 00181 Helsinki,
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Message-ID: <81ba3745-8277-d16e-3aad-48324f51dc8a@intel.com>
Date:   Fri, 30 Nov 2018 11:19:03 +0200
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On 30/11/18 9:00 AM, Du, Alek wrote:
>>From b893df3a1a937bd5fe22d39ceae93454a2e5e0e4 Mon Sep 17 00:00:00 2001
> From: Alek Du <alek.du@intel.com>
> Date: Fri, 30 Nov 2018 14:02:28 +0800
> Subject: [PATCH] sdhci: fix the fake timeout bug
> 
> We observed some fake timeouts on some devices, the log is like this:
> 
> [ 7586.290201] mmc1: Timeout waiting for hardware cmd interrupt.
> [ 7586.290420] mmc1: sdhci: ============ SDHCI REGISTER DUMP ===========
> ...
> [ 7586.291774] mmc1: sdhci: Wake-up:   0x00000000 | Clock:    0x00000203
> 
>>From the clock control register dump, we are pretty sure the clock was
> stabilized.
> 
> In other cases, we also observed:
> 
> [ 7596.530171] mmc1: Timeout waiting for hardware cmd interrupt.
> 
> and
> 
> [ 1956.534634] mmc1: Reset 0x2 never completed.
> 
> But we are pretty sure the mmc controller is working perfectly under low
> system load.
> 
> After checking the sdhci code, we found the timeout check actually has a
> little window that the CPU can be scheduled out and when it comes back,
> the original time set or check is not valid.

Commands and resets are under spin lock, so no possibility for preemption,
and certainly a few microseconds isn't going to make any difference to these
timeouts, so I don't see how this patch could help.

I recently sent a patch for GLK laptops that had BIOS issues:

	https://marc.info/?l=linux-mmc&m=154270005901609

And also some improvements to error handling:

	https://marc.info/?l=linux-mmc&m=154229013900437

If those don't help, please share more details of the actual problem.

> 
> Signed-off-by: Alek Du <alek.du@intel.com>
> ---
>  drivers/mmc/host/sdhci.c | 19 ++++++++++++++++---
>  1 file changed, 16 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
> index 99bdae53fa2e..f88c49fc574e 100644
> --- a/drivers/mmc/host/sdhci.c
> +++ b/drivers/mmc/host/sdhci.c
> @@ -218,12 +218,17 @@ void sdhci_reset(struct sdhci_host *host, u8 mask)
>  	/* hw clears the bit when it's done */
>  	while (sdhci_readb(host, SDHCI_SOFTWARE_RESET) & mask) {
>  		if (ktime_after(ktime_get(), timeout)) {
> +			/* check it again, since there is a window between
> +			   bit check and time check */
> +			if (!(sdhci_readb(host, SDHCI_SOFTWARE_RESET) & mask))
> +				break;
>  			pr_err("%s: Reset 0x%x never completed.\n",
>  				mmc_hostname(host->mmc), (int)mask);
>  			sdhci_dumpregs(host);
>  			return;
> +		} else {
> +			udelay(10);
>  		}
> -		udelay(10);
>  	}
>  }
>  EXPORT_SYMBOL_GPL(sdhci_reset);
> @@ -1395,9 +1400,10 @@ void sdhci_send_command(struct sdhci_host *host, struct mmc_command *cmd)
>  		timeout += DIV_ROUND_UP(cmd->busy_timeout, 1000) * HZ + HZ;
>  	else
>  		timeout += 10 * HZ;
> -	sdhci_mod_timer(host, cmd->mrq, timeout);
>  
>  	sdhci_writew(host, SDHCI_MAKE_CMD(cmd->opcode, flags), SDHCI_COMMAND);
> +	/* setup timer after command to avoid fake timeout */
> +	sdhci_mod_timer(host, cmd->mrq, timeout);
>  }
>  EXPORT_SYMBOL_GPL(sdhci_send_command);
>  
> @@ -1611,12 +1617,19 @@ void sdhci_enable_clk(struct sdhci_host *host, u16 clk)
>  	while (!((clk = sdhci_readw(host, SDHCI_CLOCK_CONTROL))
>  		& SDHCI_CLOCK_INT_STABLE)) {
>  		if (ktime_after(ktime_get(), timeout)) {
> +			/* check it again since there is a window between
> +			   status check and time check */
> +			if ((clk = sdhci_readw(host, SDHCI_CLOCK_CONTROL))
> +					& SDHCI_CLOCK_INT_STABLE)
> +				break;
>  			pr_err("%s: Internal clock never stabilised.\n",
>  			       mmc_hostname(host->mmc));
>  			sdhci_dumpregs(host);
>  			return;
>  		}
> -		udelay(10);
> +		else {
> +			udelay(10);
> +		}
>  	}
>  
>  	clk |= SDHCI_CLOCK_CARD_EN;
>