linux-kernel - Re: [PATCH V2] sdhci: fix the timeout check window for clock and reset

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Date:   Tue, 4 Dec 2018 14:24:42 +0200
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     "Du, Alek" <alek.du@...el.com>
Cc:     linux-mmc@...r.kernel.org, ulf.hansson@...aro.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2] sdhci: fix the timeout check window for clock and
 reset

On 4/12/18 3:01 AM, Du, Alek wrote:
>>>From 87692fc090978bde8fe872f02d0023a57af6b492 Mon Sep 17 00:00:00 2001
> From: Alek Du <alek.du@...el.com>
> Date: Fri, 30 Nov 2018 14:02:28 +0800
> Subject: [PATCH] sdhci: fix the timeout check window for clock and reset
> 
> We observed some fake timeouts on some devices, the log is like this:

Please change "fake timeouts" to "premature timeouts".  Also I think it is
worth mentioning that this was with a virtualized environment.

> 
> case 1:
> [159525.255629] mmc1: Internal clock never stabilised.
> [159525.255818] mmc1: sdhci: ============ SDHCI REGISTER DUMP ===========
> [159525.256049] mmc1: sdhci: Sys addr:  0x00000000 | Version:  0x00001002
> [159525.256277] mmc1: sdhci: Blk size:  0x00000000 | Blk cnt:  0x00000000
> [159525.256523] mmc1: sdhci: Argument:  0x00000000 | Trn mode: 0x00000000
> [159525.256752] mmc1: sdhci: Present:   0x1fff0000 | Host ctl: 0x00000000
> [159525.256979] mmc1: sdhci: Power:     0x0000000b | Blk gap:  0x00000080
> [159525.257205] mmc1: sdhci: Wake-up:   0x00000000 | Clock:    0x0000fa03
>>>From the clock control register dump, we are pretty sure the clock was
> stablized.
> 
> case 2:
> [  914.550127] mmc1: Reset 0x2 never completed.
> [  914.550321] mmc1: sdhci: ============ SDHCI REGISTER DUMP ===========
> [  914.550608] mmc1: sdhci: Sys addr:  0x00000010 | Version:  0x00001002
> 
> 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.
> 
> Signed-off-by: Alek Du <alek.du@...el.com>

Please add fixes tag:

Fixes: 5a436cc0af62 ("mmc: sdhci: Optimize delay loops")

And also a stable tag:

Cc: stable@...r.kernel.org      # v4.12+

> ---
>  drivers/mmc/host/sdhci.c | 16 ++++++++++++++--
>  1 file changed, 14 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
> index 99bdae53fa2e..af01f7d16eae 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;

It would be neater like:

	while (1) {
		bool timedout = ktime_after(ktime_get(), timeout);

		if (!(sdhci_readb(host, SDHCI_SOFTWARE_RESET) & mask))
			break;
		if (timedout) {


>  			pr_err("%s: Reset 0x%x never completed.\n",
>  				mmc_hostname(host->mmc), (int)mask);
>  			sdhci_dumpregs(host);
>  			return;
> +		} else {

The if-clause does a 'return', so the 'else' is not needed

> +			udelay(10);
>  		}
> -		udelay(10);
>  	}
>  }
>  EXPORT_SYMBOL_GPL(sdhci_reset);
> @@ -1611,12 +1616,19 @@ 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;

Similarly:

	while (1) {
		bool timedout = ktime_after(ktime_get(), timeout);

		clk = sdhci_readw(host, SDHCI_CLOCK_CONTROL);
		if (clk & SDHCI_CLOCK_INT_STABLE)
			break;
		if (timedout) {


>  			pr_err("%s: Internal clock never stabilised.\n",
>  			       mmc_hostname(host->mmc));
>  			sdhci_dumpregs(host);
>  			return;
>  		}
> -		udelay(10);
> +		else {

The if-clause does a 'return', so the 'else' is not needed

> +			udelay(10);
> +		}
>  	}
>  
>  	clk |= SDHCI_CLOCK_CARD_EN;
>