linux-kernel - Re: [PATCH V3] sdhci: fix the timeout check window for clock and reset

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Date:   Wed, 5 Dec 2018 13:16:27 +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 V3] sdhci: fix the timeout check window for clock and
 reset

On 5/12/18 5:14 AM, Du, Alek wrote:
>>>From bcb38577961823b4f8f2cc0aec7dd450a81b6ddc 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 premature timeouts on a virtualization platform, the log
> is like this:
> 
> 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
> ...
> [159525.257205] 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.
> 
> Fixes: 5a436cc0af62 ("mmc: sdhci: Optimize delay loops")
> Signed-off-by: Alek Du <alek.du@...el.com>
> Cc: stable@...r.kernel.org      # v4.12+

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

> ---
>  drivers/mmc/host/sdhci.c | 18 +++++++++++++-----
>  1 file changed, 13 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
> index 99bdae53fa2e..451b08a818a9 100644
> --- a/drivers/mmc/host/sdhci.c
> +++ b/drivers/mmc/host/sdhci.c
> @@ -216,8 +216,12 @@ void sdhci_reset(struct sdhci_host *host, u8 mask)
>  	timeout = ktime_add_ms(ktime_get(), 100);
>  
>  	/* hw clears the bit when it's done */
> -	while (sdhci_readb(host, SDHCI_SOFTWARE_RESET) & mask) {
> -		if (ktime_after(ktime_get(), timeout)) {
> +	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);
> @@ -1608,9 +1612,13 @@ void sdhci_enable_clk(struct sdhci_host *host, u16 clk)
>  
>  	/* Wait max 20 ms */
>  	timeout = ktime_add_ms(ktime_get(), 20);
> -	while (!((clk = sdhci_readw(host, SDHCI_CLOCK_CONTROL))
> -		& SDHCI_CLOCK_INT_STABLE)) {
> -		if (ktime_after(ktime_get(), timeout)) {
> +	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);
>