linux-kernel - [PATCH v1 7/7] i2c-mlxbf.c: support lock mechanism

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Date:   Tue, 16 Aug 2022 18:54:12 -0400
From:   Asmaa Mnebhi <asmaa@...dia.com>
To:     Wolfram Sang <wsa+renesas@...g-engineering.com>,
        linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Asmaa Mnebhi <asmaa@...dia.com>,
        Khalil Blaiech <kblaiech@...dia.com>
Subject: [PATCH v1 7/7] i2c-mlxbf.c: support lock mechanism

Linux is not the only entity using the BlueField I2C busses so
support a lock mechanism provided by hardware to avoid issues
when multiple entities are trying to access the same bus.

The lock is acquired whenever written explicitely or the lock register
is read. So make sure it is always released at the end of a
successful or failed transaction.

Reviewed-by: Khalil Blaiech <kblaiech@...dia.com>
Signed-off-by: Asmaa Mnebhi <asmaa@...dia.com>
---
 drivers/i2c/busses/i2c-mlxbf.c | 42 ++++++++++++++++++++++++++++++----
 1 file changed, 38 insertions(+), 4 deletions(-)

diff --git a/drivers/i2c/busses/i2c-mlxbf.c b/drivers/i2c/busses/i2c-mlxbf.c
index cc87c2511678..aa0ea41e7bfd 100644
--- a/drivers/i2c/busses/i2c-mlxbf.c
+++ b/drivers/i2c/busses/i2c-mlxbf.c
@@ -296,6 +296,7 @@
  * exact.
  */
 #define MLXBF_I2C_SMBUS_TIMEOUT   (300 * 1000) /* 300ms */
+#define MLXBF_I2C_SMBUS_LOCK_POLL_TIMEOUT (300 * 1000) /* 300ms */
 
 /* Polling frequency in microseconds. */
 #define MLXBF_I2C_POLL_FREQ_IN_USEC        200
@@ -523,6 +524,25 @@ static bool mlxbf_i2c_smbus_master_wait_for_idle(struct mlxbf_i2c_priv *priv)
 	return false;
 }
 
+/*
+ * wait for the lock to be released before acquiring it.
+ */
+static bool mlxbf_i2c_smbus_master_lock(struct mlxbf_i2c_priv *priv)
+{
+	if (mlxbf_i2c_poll(priv->mst->io, MLXBF_I2C_SMBUS_MASTER_GW,
+			   MLXBF_I2C_MASTER_LOCK_BIT, true,
+			   MLXBF_I2C_SMBUS_LOCK_POLL_TIMEOUT))
+		return true;
+
+	return false;
+}
+
+static void mlxbf_i2c_smbus_master_unlock(struct mlxbf_i2c_priv *priv)
+{
+	/* Clear the gw to clear the lock */
+	writel(0, priv->mst->io + MLXBF_I2C_SMBUS_MASTER_GW);
+}
+
 static bool mlxbf_i2c_smbus_transaction_success(u32 master_status,
 						u32 cause_status)
 {
@@ -725,10 +745,18 @@ mlxbf_i2c_smbus_start_transaction(struct mlxbf_i2c_priv *priv,
 	slave = request->slave & GENMASK(6, 0);
 	addr = slave << 1;
 
-	/* First of all, check whether the HW is idle. */
-	if (WARN_ON(!mlxbf_i2c_smbus_master_wait_for_idle(priv)))
+	/* Try to acquire the smbus gw lock before any reads of the GW register since
+	 * a read sets the lock.
+	 */
+	if (WARN_ON(!mlxbf_i2c_smbus_master_lock(priv)))
 		return -EBUSY;
 
+	/* Check whether the HW is idle */
+	if (WARN_ON(!mlxbf_i2c_smbus_master_wait_for_idle(priv))) {
+		mlxbf_i2c_smbus_master_unlock(priv);
+		return -EBUSY;
+	}
+
 	/* Set first byte. */
 	data_desc[data_idx++] = addr;
 
@@ -752,8 +780,10 @@ mlxbf_i2c_smbus_start_transaction(struct mlxbf_i2c_priv *priv,
 			write_en = 1;
 			write_len += operation->length;
 			if (data_idx + operation->length >
-					MLXBF_I2C_MASTER_DATA_DESC_SIZE)
+					MLXBF_I2C_MASTER_DATA_DESC_SIZE) {
+				mlxbf_i2c_smbus_master_unlock(priv);
 				return -ENOBUFS;
+			}
 			memcpy(data_desc + data_idx,
 			       operation->buffer, operation->length);
 			data_idx += operation->length;
@@ -784,8 +814,10 @@ mlxbf_i2c_smbus_start_transaction(struct mlxbf_i2c_priv *priv,
 	if (write_en) {
 		ret = mlxbf_i2c_smbus_enable(priv, slave, write_len, block_en,
 					 pec_en, 0);
-		if (ret)
+		if (ret) {
+			mlxbf_i2c_smbus_master_unlock(priv);
 			return ret;
+		}
 	}
 
 	if (read_en) {
@@ -812,6 +844,8 @@ mlxbf_i2c_smbus_start_transaction(struct mlxbf_i2c_priv *priv,
 			priv->mst->io + priv->chip->smbus_master_fsm_off);
 	}
 
+	mlxbf_i2c_smbus_master_unlock(priv);
+
 	return ret;
 }
 
-- 
2.30.1