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Message-ID:
<BY5PR08MB6296FC84911F1B2F63AC04DAF1D1A@BY5PR08MB6296.namprd08.prod.outlook.com>
Date: Tue, 25 Nov 2025 18:30:35 +0000
From: "Jens Stobernack (Nokia)" <jens.stobernack@...ia.com>
To: "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>
CC: "nhorman@...driver.com" <nhorman@...driver.com>, "andi.shyti@...nel.org"
<andi.shyti@...nel.org>, "linux-kernel@...r.kernel.org"
<linux-kernel@...r.kernel.org>, "vasilykh@...sta.com" <vasilykh@...sta.com>
Subject: [PATCH] i2c: ismt: add i2c bus recovery on timed out transaction
In rare occasions the i2c controller will get stuck. This failure is
described in commit 46b2dfc0aa79 ("i2c: ismt: kill transaction in hardware
on timeout")
The kill operation never resolved the stuck condition in lab testing. A
traditional i2c bus recovery was required to recover the i2c
controller and allow it to continue operating as normal.
Signed-off-by: Jens Stobernack <jens.stobernack@...ia.com>
---
drivers/i2c/busses/i2c-ismt.c | 128 ++++++++++++++++++++++++++++++++++
1 file changed, 128 insertions(+)
diff --git a/drivers/i2c/busses/i2c-ismt.c b/drivers/i2c/busses/i2c-ismt.c
index 7aaefb21416a..4bdeb865d569 100644
--- a/drivers/i2c/busses/i2c-ismt.c
+++ b/drivers/i2c/busses/i2c-ismt.c
@@ -122,12 +122,17 @@
/* iSMT Miscellaneous Registers */
#define ISMT_SPGT 0x300 /* SMBus PHY Global Timing */
+#define ISMT_DBCTRL 0x388 /* Discrete Data Bus Control */
+#define ISMT_DBSTS 0x38C /* Discrete Data Bus Status */
/* General Control Register (GCTRL) bit definitions */
#define ISMT_GCTRL_TRST 0x04 /* Target Reset */
#define ISMT_GCTRL_KILL 0x08 /* Kill */
#define ISMT_GCTRL_SRST 0x40 /* Soft Reset */
+/* Error Status Register (ERRSTS) bit definitions */
+#define ISMT_ERRSTS_CKLTO (0x1 << 24) /* Clock low timeout */
+
/* Master Control Register (MCTRL) bit definitions */
#define ISMT_MCTRL_SS 0x01 /* Start/Stop */
#define ISMT_MCTRL_MEIE 0x10 /* Master Error Interrupt Enable */
@@ -153,6 +158,20 @@
/* MSI Control Register (MSICTL) bit definitions */
#define ISMT_MSICTL_MSIE 0x01 /* MSI Enable */
+/* Bit Bang Databus Control (DBCTRL) bit definitions */
+#define ISMT_DBCTRL_EN 0x80000000 /* Enable bit banging */
+#define ISMT_DBCTRL_SMBDT 0x00000001 /* SMB Data signal, 0 mean data low */
+#define ISMT_DBCTRL_SMBCK 0x00000002 /* SMB Clock signal, 0 means clock low */
+
+/* Bit Bang Databus Status (DBSTS) bit definitions */
+#define ISMT_DBSTS_LSMBS_MASK 0x00000007 /* Last SMBus state, use with care */
+#define ISMT_DBSTS_SMBDC 0x00000040 /* SMBus Data Change */
+#define ISMT_DBSTS_SMBCKC 0x00000080 /* SMBus Clock Change */
+#define ISMT_DBSTS_SMBDT 0x00000100 /* Live state of SMBus data signal */
+#define ISMT_DBSTS_SMBDT_SHIFT 8
+#define ISMT_DBSTS_SMBCK 0x00000200 /* Live state of SMBus clock signal */
+#define ISMT_DBSTS_SMBCK_SHIFT 9
+
/* iSMT Hardware Descriptor */
struct ismt_desc {
u8 tgtaddr_rw; /* target address & r/w bit */
@@ -633,6 +652,7 @@ static int ismt_access(struct i2c_adapter *adap, u16 addr,
if (unlikely(!time_left)) {
ismt_kill_transaction(priv);
+ i2c_recover_bus(&priv->adapter);
ret = -ETIMEDOUT;
goto out;
}
@@ -670,6 +690,113 @@ static const struct i2c_algorithm smbus_algorithm = {
.functionality = ismt_func,
};
+/**
+ * ismt_i2c_get_scl() - get the scl state
+ * @adap: the i2c host adapter
+ */
+static int ismt_i2c_get_scl(struct i2c_adapter *adap)
+{
+ struct ismt_priv *priv = i2c_get_adapdata(adap);
+ unsigned int reg;
+
+ reg = readl(priv->smba + ISMT_DBSTS) & ISMT_DBSTS_SMBCK;
+ reg >>= ISMT_DBSTS_SMBCK_SHIFT;
+ return reg;
+}
+
+/**
+ * ismt_i2c_set_scl() - set the scl state
+ * @adap: the i2c host adapter
+ * @val: the pin state
+ */
+static void ismt_i2c_set_scl(struct i2c_adapter *adap, int val)
+{
+ struct ismt_priv *priv = i2c_get_adapdata(adap);
+ unsigned int reg;
+
+ reg = readl(priv->smba + ISMT_DBCTRL);
+ if (val == 0)
+ reg &= ~ISMT_DBCTRL_SMBCK;
+ else
+ reg |= ISMT_DBCTRL_SMBCK;
+ writel(reg, priv->smba + ISMT_DBCTRL);
+}
+
+/**
+ * ismt_i2c_get_sda() - get the sda state
+ * @adap: the i2c host adapter
+ */
+static int ismt_i2c_get_sda(struct i2c_adapter *adap)
+{
+ struct ismt_priv *priv = i2c_get_adapdata(adap);
+ unsigned int reg;
+
+ reg = readl(priv->smba + ISMT_DBSTS) & ISMT_DBSTS_SMBDT;
+ reg >>= ISMT_DBSTS_SMBDT_SHIFT;
+ return reg;
+}
+
+/**
+ * ismt_i2c_set_sda() - set the sda state
+ * @adap: the i2c host adapter
+ * @val: the pin state
+ */
+static void ismt_i2c_set_sda(struct i2c_adapter *adap, int val)
+{
+ struct ismt_priv *priv = i2c_get_adapdata(adap);
+ unsigned int reg;
+
+ reg = readl(priv->smba + ISMT_DBCTRL);
+ if (val == 0)
+ reg &= ~ISMT_DBCTRL_SMBDT;
+ else
+ reg |= ISMT_DBCTRL_SMBDT;
+ writel(reg, priv->smba + ISMT_DBCTRL);
+}
+
+/**
+ * ismt_i2c_prepare_recovery() - configure bit banging mode
+ * @adap: the i2c host adapter
+ */
+static void ismt_i2c_prepare_recovery(struct i2c_adapter *adap)
+{
+ struct ismt_priv *priv = i2c_get_adapdata(adap);
+ unsigned int reg;
+
+ /* Enable bit banging, datasheet recommends setting EN without
+ * changing the values of SMBDT and SMBCK.
+ */
+ reg = readl(priv->smba + ISMT_DBCTRL);
+ writel(reg | ISMT_DBCTRL_EN, priv->smba + ISMT_DBCTRL);
+}
+
+/**
+ * ismt_i2c_prepare_recovery() - clear bit banging mode
+ * @adap: the i2c host adapter
+ */
+static void ismt_i2c_unprepare_recovery(struct i2c_adapter *adap)
+{
+ struct ismt_priv *priv = i2c_get_adapdata(adap);
+ unsigned int reg;
+
+ // Disable bit banging
+ reg = readl(priv->smba + ISMT_DBCTRL);
+ writel(reg & ~ISMT_DBCTRL_EN, priv->smba + ISMT_DBCTRL);
+
+ // Clear the expected clock low timeout
+ writel(ISMT_ERRSTS_CKLTO, priv->smba + ISMT_GR_ERRSTS);
+}
+
+static struct i2c_bus_recovery_info ismt_i2c_recovery_info = {
+ .recover_bus = i2c_generic_scl_recovery,
+ .get_scl = ismt_i2c_get_scl,
+ .set_scl = ismt_i2c_set_scl,
+ .get_sda = ismt_i2c_get_sda,
+ .set_sda = ismt_i2c_set_sda,
+ .prepare_recovery = ismt_i2c_prepare_recovery,
+ .unprepare_recovery = ismt_i2c_unprepare_recovery,
+};
+
/**
* ismt_handle_isr() - interrupt handler bottom half
* @priv: iSMT private data
@@ -899,6 +1026,7 @@ ismt_probe(struct pci_dev *pdev, const struct pci_device_id *id)
priv->adapter.dev.parent = &pdev->dev;
ACPI_COMPANION_SET(&priv->adapter.dev, ACPI_COMPANION(&pdev->dev));
priv->adapter.retries = ISMT_MAX_RETRIES;
+ priv->adapter.bus_recovery_info = &ismt_i2c_recovery_info;
priv->pci_dev = pdev;
--
2.43.0
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