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

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Message-Id: <20221117094859.20582-1-quic_sartgarg@quicinc.com>
Date:   Thu, 17 Nov 2022 15:18:48 +0530
From:   Sarthak Garg <quic_sartgarg@...cinc.com>
To:     adrian.hunter@...el.com, ulf.hansson@...aro.org
Cc:     linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, quic_rampraka@...cinc.com,
        quic_pragalla@...cinc.com, quic_sayalil@...cinc.com,
        Sarthak Garg <quic_sartgarg@...cinc.com>,
        Wolfram Sang <wsa+renesas@...g-engineering.com>,
        "Darrick J. Wong" <djwong@...nel.org>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Shaik Sajida Bhanu <quic_c_sbhanu@...cinc.com>
Subject: [PATCH V1] mmc: core: Wait for 1ms after enabling the clocks post voltage switch

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@...cinc.com>
---
 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