[PATCH v2 2/3] i2c: qcom-geni: Add bus recovery support for FIFO mode

[Aniket Randive]

I2C transfers in FIFO mode can fail with -EPROTO, -ETIMEDOUT or
-EAGAIN when a target holds SDA low, leaving the bus stuck and
preventing subsequent transactions.

Add bus recovery support using the I2C_BUS_CLEAR and I2C_STOP_ON_BUS
hardware opcodes to restore the bus to an idle state. Check the SDA
line state through SE_GENI_IOS.RX_DATA_IN and skip recovery when the
bus is already free. Trigger recovery automatically from
geni_i2c_xfer() on -EPROTO, -ETIMEDOUT and -EAGAIN (arbitration-lost)
errors, and register the recovery callback through i2c_bus_recovery_info
to allow recovery via i2c_recover_bus().

This adds bus recovery support for FIFO mode only.

Signed-off-by: Aniket Randive <aniket.randive@xxxxxxxxxxxxxxxx>
---
 drivers/i2c/busses/i2c-qcom-geni.c | 119 ++++++++++++++++++++++++++++++++++++-
 1 file changed, 118 insertions(+), 1 deletion(-)

diff --git a/drivers/i2c/busses/i2c-qcom-geni.c b/drivers/i2c/busses/i2c-qcom-geni.c
index 60b6273f538c..065d7240de04 100644
--- a/drivers/i2c/busses/i2c-qcom-geni.c
+++ b/drivers/i2c/busses/i2c-qcom-geni.c
@@ -34,6 +34,7 @@
 #define I2C_READ		0x2
 #define I2C_WRITE_READ		0x3
 #define I2C_ADDR_ONLY		0x4
+#define I2C_BUS_FREE		(RX_DATA_IN | IO2_DATA_IN)
 /* M_CMD params for I2C */
 #define PRE_CMD_DELAY		BIT(0)
 #define TIMESTAMP_BEFORE	BIT(1)
@@ -145,6 +146,7 @@ struct geni_i2c_dev {
 	u32 num_msgs;
 	struct geni_i2c_gpi_multi_desc_xfer i2c_multi_desc_config;
 	const struct geni_i2c_desc *dev_data;
+	struct i2c_bus_recovery_info rinfo;
 };
 
 struct geni_i2c_err_log {
@@ -316,7 +318,7 @@ static void geni_i2c_check_addr_data_nack(struct geni_i2c_dev *gi2c)
 {
 	if (!readl_relaxed(gi2c->se.base + SE_GENI_M_GP_LENGTH))
 		geni_i2c_err(gi2c, ADDR_NACK);
-	else if (!(gi2c->cur->flags & I2C_M_RD))
+	else if (gi2c->cur && !(gi2c->cur->flags & I2C_M_RD))
 		geni_i2c_err(gi2c, DATA_NACK);
 }
 
@@ -1013,6 +1015,107 @@ static int geni_i2c_fifo_xfer(struct geni_i2c_dev *gi2c,
 	return num;
 }
 
+static int geni_i2c_fifo_bus_cmd(struct geni_i2c_dev *gi2c, u32 cmd)
+{
+	unsigned long time_left;
+	unsigned long flags;
+
+	/*
+	 * Clear cur so the IRQ handler does not attempt FIFO watermark
+	 * filling or draining while the recovery opcode is in flight.
+	 * cur and err are shared with geni_i2c_irq(), which reads cur and
+	 * writes err under gi2c->lock, so take the lock around this reset.
+	 */
+	spin_lock_irqsave(&gi2c->lock, flags);
+	gi2c->cur = NULL;
+	gi2c->err = 0;
+	spin_unlock_irqrestore(&gi2c->lock, flags);
+	geni_se_select_mode(&gi2c->se, GENI_SE_FIFO);
+	reinit_completion(&gi2c->done);
+
+	geni_se_setup_m_cmd(&gi2c->se, cmd, 0);
+	time_left = wait_for_completion_timeout(&gi2c->done, XFER_TIMEOUT);
+	if (!time_left) {
+		dev_err(gi2c->se.dev, "timeout waiting for bus cmd %u\n", cmd);
+		geni_i2c_abort_xfer(gi2c);
+
+		return -ETIMEDOUT;
+	}
+
+	/*
+	 * ARB_LOST and BUS_PROTO interrupts may be reported while the bus
+	 * transitions from stuck to idle during the recovery sequence.
+	 * The opcode completed successfully so treat these as success.
+	 */
+	if (gi2c->err == -EAGAIN || gi2c->err == -EPROTO)
+		return 0;
+
+	return gi2c->err;
+}
+
+static bool geni_i2c_bus_is_free(struct geni_i2c_dev *gi2c)
+{
+	return (readl_relaxed(gi2c->se.base + SE_GENI_IOS) & I2C_BUS_FREE) ==
+	       I2C_BUS_FREE;
+}
+
+static bool geni_i2c_needs_bus_recovery(struct geni_i2c_dev *gi2c, int ret)
+{
+	/*
+	 * -EPROTO and -ETIMEDOUT indicate bus errors where the target may be
+	 * holding a bus line low. ARB_LOST (-EAGAIN) on a single-controller
+	 * bus indicates a stuck target, not a real arbitration loss.
+	 * GPI DMA mode extends this trigger separately.
+	 */
+	return !gi2c->gpi_mode &&
+	       (ret == -EPROTO || ret == -ETIMEDOUT || ret == -EAGAIN) &&
+	       !geni_i2c_bus_is_free(gi2c);
+}
+
+static int geni_i2c_recover_bus(struct i2c_adapter *adap)
+{
+	struct geni_i2c_dev *gi2c = i2c_get_adapdata(adap);
+	u32 ios;
+	int ret;
+
+	ret = pm_runtime_get_sync(gi2c->se.dev);
+	if (ret < 0) {
+		dev_err(gi2c->se.dev, "bus recovery failed, error turning SE resources:%d\n", ret);
+		pm_runtime_put_noidle(gi2c->se.dev);
+		return ret;
+	}
+
+	if (geni_i2c_bus_is_free(gi2c)) {
+		pm_runtime_put_autosuspend(gi2c->se.dev);
+		return 0;
+	}
+
+	/* Bus clear cannot recover a target holding SCL low. */
+	ios = readl_relaxed(gi2c->se.base + SE_GENI_IOS);
+	if (!(ios & IO2_DATA_IN)) {
+		pm_runtime_put_autosuspend(gi2c->se.dev);
+		return -EBUSY;
+	}
+
+	ret = geni_i2c_fifo_bus_cmd(gi2c, I2C_BUS_CLEAR);
+	if (!ret)
+		ret = geni_i2c_fifo_bus_cmd(gi2c, I2C_STOP_ON_BUS);
+
+	/*
+	 * Recovery succeeds only once both bus lines are released. The bus
+	 * state is the authority, while a clean opcode status with either
+	 * line low is a failed recovery.
+	 */
+	if (geni_i2c_bus_is_free(gi2c))
+		ret = 0;
+	else if (!ret)
+		ret = -EBUSY;
+
+	pm_runtime_put_autosuspend(gi2c->se.dev);
+
+	return ret;
+}
+
 static int geni_i2c_xfer(struct i2c_adapter *adap,
 			 struct i2c_msg msgs[],
 			 int num)
@@ -1037,6 +1140,15 @@ static int geni_i2c_xfer(struct i2c_adapter *adap,
 	else
 		ret = geni_i2c_fifo_xfer(gi2c, msgs, num);
 
+	if (geni_i2c_needs_bus_recovery(gi2c, ret)) {
+		int recovery_ret = i2c_recover_bus(adap);
+
+		if (recovery_ret)
+			dev_err(gi2c->se.dev,
+				"bus recovery failed: %d (xfer error: %d)\n",
+				recovery_ret, ret);
+	}
+
 out_pm:
 	pm_runtime_put_autosuspend(gi2c->se.dev);
 	gi2c->cur = NULL;
@@ -1239,6 +1351,11 @@ static int geni_i2c_probe(struct platform_device *pdev)
 	if (ret < 0)
 		return ret;
 
+	if (!gi2c->gpi_mode) {
+		gi2c->rinfo.recover_bus = geni_i2c_recover_bus;
+		gi2c->adap.bus_recovery_info = &gi2c->rinfo;
+	}
+
 	ret = i2c_add_adapter(&gi2c->adap);
 	if (ret) {
 		release_gpi_dma(gi2c);

-- 
2.34.1