[PATCH V1] mmc: core: Wait for 1ms after enabling the clocks post voltage switch

[Sarthak Garg]

As per spec we should wait for 1ms after providing the SD clock to the
card again as part of voltage switch sequence but there seems to be a
violation here. Clocks are getting gated before 1ms as part of
sdhci_set_ios function where we try to reset SD Clock Enable by
resetting SDHCI_CLOCK_CARD_EN bit in SDHCI_CLOCK_CONTROL register
leading to voltage switch failures for specific SD cards.
Below ftraces also confirms the above understanding :

9.511367: mmc_host_set_uhs_voltage: mmc1 called
9.511369: mmc_set_ios: mmc1: clock 0Hz busmode 2 powermode 2 cs 0
Vdd 18 width 1 timing 0
9.511370: sdhci_set_ios: mmc1 called
9.511370: sdhci_set_ios: mmc1 setting clock ios->clock: 0 host->clock:
400000
9.511372: sdhci_msm_set_clock: mmc1 clock: 0
9.511394: sdhci_set_ios: mmc1 gating clocks by writing
~SDHCI_CLOCK_CARD_EN to SDHCI_CLOCK_CONTROL register
9.511413: sdhci_msm_set_clock: mmc1 clock: 0
9.511423: mmc_set_signal_voltage: mmc1 called
9.533816: mmc_set_ios: mmc1: clock 400000Hz busmode 2 powermode 2 cs 0
Vdd 18 width 1 timing 0
9.533820: sdhci_set_ios: mmc1 called
9.533822: sdhci_set_ios: mmc1 setting clock ios->clock: 400000
host->clock: 0
9.533826: sdhci_msm_set_clock: mmc1 clock: 400000
9.533925: sdhci_enable_clk: mmc1 Enabling clocks by writing
SDHCI_CLOCK_CARD_EN to SDHCI_CLOCK_CONTROL register
9.533950: sdhci_set_ios: mmc1 gating clocks by writing
~SDHCI_CLOCK_CARD_EN to SDHCI_CLOCK_CONTROL register
9.533973: sdhci_msm_set_clock: mmc1 clock: 400000
9.534043: sdhci_enable_clk: mmc1 Enabling clocks by writing
SDHCI_CLOCK_CARD_EN to SDHCI_CLOCK_CONTROL register
9.534045: mmc_host_set_uhs_voltage: mmc1 Done

Wait for 1ms after enabling the clock post voltage switch to make sure
clock is kept alive for alteast 1ms as per spec.

Signed-off-by: Sarthak Garg <quic_sartgarg@xxxxxxxxxxx>
---
 drivers/mmc/core/core.c  | 4 ++++
 drivers/mmc/host/sdhci.c | 3 +++
 include/linux/mmc/host.h | 1 +
 3 files changed, 8 insertions(+)

diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
index a1efda85c6f2..d63e00aab6cb 100644
--- a/drivers/mmc/core/core.c
+++ b/drivers/mmc/core/core.c
@@ -1181,6 +1181,8 @@ int mmc_host_set_uhs_voltage(struct mmc_host *host)
 	host->ios.clock = 0;
 	mmc_set_ios(host);
 
+	host->doing_signal_voltage_switch = true;
+
 	if (mmc_set_signal_voltage(host, MMC_SIGNAL_VOLTAGE_180))
 		return -EAGAIN;
 
@@ -1189,6 +1191,8 @@ int mmc_host_set_uhs_voltage(struct mmc_host *host)
 	host->ios.clock = clock;
 	mmc_set_ios(host);
 
+	host->doing_signal_voltage_switch = false;
+
 	return 0;
 }
 
diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
index fb6e9a81f198..ac7c254eef4b 100644
--- a/drivers/mmc/host/sdhci.c
+++ b/drivers/mmc/host/sdhci.c
@@ -2312,6 +2312,9 @@ void sdhci_set_ios(struct mmc_host *mmc, struct mmc_ios *ios)
 		host->ops->set_clock(host, ios->clock);
 		host->clock = ios->clock;
 
+		if (mmc->doing_signal_voltage_switch)
+			usleep_range(1000, 1250);
+
 		if (host->quirks & SDHCI_QUIRK_DATA_TIMEOUT_USES_SDCLK &&
 		    host->clock) {
 			host->timeout_clk = mmc->actual_clock ?
diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h
index 8fdd3cf971a3..06c88cd7a8bf 100644
--- a/include/linux/mmc/host.h
+++ b/include/linux/mmc/host.h
@@ -521,6 +521,7 @@ struct mmc_host {
 	bool			hsq_enabled;
 
 	u32			err_stats[MMC_ERR_MAX];
+	bool			doing_signal_voltage_switch;
 	unsigned long		private[] ____cacheline_aligned;
 };
 
-- 
2.17.1