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Subject[PATCH] mmc: sdhci: fix the timeout check window for clock and reset
Date
From: Alek Du <alek.du@intel.com>

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")
Cc: stable@vger.kernel.org # v4.12+
Signed-off-by: Alek Du <alek.du@intel.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);
--
2.17.1
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