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

Adrian Hunter
2018-12-04T12:24:42Z

On 4/12/18 3:01 AM, Du, Alek wrote:
>>From 87692fc090978bde8fe872f02d0023a57af6b492 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 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@intel.com>

Please add fixes tag:

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

And also a stable tag:

Cc: stable@vger.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;
>