[PATCH 9/9] i2c: riic: Implement bus recovery

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From: Lad Prabhakar <prabhakar.mahadev-lad.rj@xxxxxxxxxxxxxx>

Implement bus recovery by reinitializing the hardware to reset the bus
state and generating 9 clock cycles (and a stop condition) to release
the SDA line.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@xxxxxxxxxxxxxx>
---
 drivers/i2c/busses/i2c-riic.c | 100 ++++++++++++++++++++++++++++++----
 1 file changed, 90 insertions(+), 10 deletions(-)

diff --git a/drivers/i2c/busses/i2c-riic.c b/drivers/i2c/busses/i2c-riic.c
index 919da1bdcce5..cfb57e1de01b 100644
--- a/drivers/i2c/busses/i2c-riic.c
+++ b/drivers/i2c/busses/i2c-riic.c
@@ -50,6 +50,7 @@
 
 #define ICCR1_ICE	BIT(7)
 #define ICCR1_IICRST	BIT(6)
+#define ICCR1_CLO	BIT(5)
 #define ICCR1_SOWP	BIT(4)
 #define ICCR1_SCLI	BIT(1)
 #define ICCR1_SDAI	BIT(0)
@@ -68,6 +69,7 @@
 #define ICMR3_ACKBT	BIT(3)
 
 #define ICFER_FMPE	BIT(7)
+#define ICFER_MALE	BIT(1)
 
 #define ICIER_TIE	BIT(7)
 #define ICIER_TEIE	BIT(6)
@@ -81,6 +83,8 @@
 
 #define RIIC_INIT_MSG	-1
 
+#define RIIC_RECOVERY_CLK_CNT	9
+
 enum riic_reg_list {
 	RIIC_ICCR1 = 0,
 	RIIC_ICCR2,
@@ -150,13 +154,16 @@ static int riic_bus_barrier(struct riic_dev *riic)
 	ret = readb_poll_timeout(riic->base + riic->info->regs[RIIC_ICCR2], val,
 				 !(val & ICCR2_BBSY), 10, riic->adapter.timeout);
 	if (ret)
-		return -EBUSY;
+		goto i2c_recover;
 
 	if (!(riic_readb(riic, RIIC_ICCR1) & ICCR1_SDAI) ||
 	    !(riic_readb(riic, RIIC_ICCR1) & ICCR1_SCLI))
-		return -EBUSY;
+		goto i2c_recover;
 
 	return 0;
+
+i2c_recover:
+	return i2c_recover_bus(&riic->adapter);
 }
 
 static int riic_xfer(struct i2c_adapter *adap, struct i2c_msg msgs[], int num)
@@ -332,7 +339,7 @@ static const struct i2c_algorithm riic_algo = {
 	.functionality = riic_func,
 };
 
-static int riic_init_hw(struct riic_dev *riic)
+static int riic_init_hw(struct riic_dev *riic, bool recover)
 {
 	int ret;
 	unsigned long rate;
@@ -414,9 +421,11 @@ static int riic_init_hw(struct riic_dev *riic)
 		 rate / total_ticks, ((brl + 3) * 100) / (brl + brh + 6),
 		 t->scl_fall_ns / ns_per_tick, t->scl_rise_ns / ns_per_tick, cks, brl, brh);
 
-	ret = pm_runtime_resume_and_get(dev);
-	if (ret)
-		return ret;
+	if (!recover) {
+		ret = pm_runtime_resume_and_get(dev);
+		if (ret)
+			return ret;
+	}
 
 	/* Changing the order of accessing IICRST and ICE may break things! */
 	riic_writeb(riic, ICCR1_IICRST | ICCR1_SOWP, RIIC_ICCR1);
@@ -434,8 +443,74 @@ static int riic_init_hw(struct riic_dev *riic)
 
 	riic_clear_set_bit(riic, ICCR1_IICRST, 0, RIIC_ICCR1);
 
-	pm_runtime_mark_last_busy(dev);
-	pm_runtime_put_autosuspend(dev);
+	if (!recover) {
+		pm_runtime_mark_last_busy(dev);
+		pm_runtime_put_autosuspend(dev);
+	}
+	return 0;
+}
+
+static int riic_recover_bus(struct i2c_adapter *adap)
+{
+	struct riic_dev *riic = i2c_get_adapdata(adap);
+	struct device *dev = riic->adapter.dev.parent;
+	int ret;
+	u8 val;
+
+	ret = riic_init_hw(riic, true);
+	if (ret)
+		return -EINVAL;
+
+	/* output extra SCL clock cycles with master arbitration-lost detection disabled */
+	riic_clear_set_bit(riic, ICFER_MALE, 0, RIIC_ICFER);
+
+	for (unsigned int i = 0; i < RIIC_RECOVERY_CLK_CNT; i++) {
+		riic_clear_set_bit(riic, 0, ICCR1_CLO, RIIC_ICCR1);
+		ret = readb_poll_timeout(riic->base + riic->info->regs[RIIC_ICCR1], val,
+					 !(val & ICCR1_CLO), 0, 100);
+		if (ret) {
+			dev_err(dev, "SCL clock cycle timeout\n");
+			return ret;
+		}
+	}
+
+	/*
+	 * The last clock cycle may have driven the SDA line high, so add a
+	 * short delay to allow the line to stabilize before checking the status.
+	 */
+	udelay(5);
+
+	/*
+	 * If an incomplete byte write occurs, the SDA line may remain low
+	 * even after 9 clock pulses, indicating the bus is not released.
+	 * To resolve this, send an additional clock pulse to simulate a STOP
+	 * condition and ensure proper bus release.
+	 */
+	if (!(riic_readb(riic, RIIC_ICCR1) & ICCR1_SDAI) &&
+	    (riic_readb(riic, RIIC_ICCR1) & ICCR1_SCLI)) {
+		riic_clear_set_bit(riic, 0, ICCR1_CLO, RIIC_ICCR1);
+		ret = readb_poll_timeout(riic->base + riic->info->regs[RIIC_ICCR1], val,
+					 !(val & ICCR1_CLO), 0, 100);
+		if (ret) {
+			dev_err(dev, "SCL clock cycle timeout occurred while issuing the STOP condition\n");
+			return ret;
+		}
+		/* delay to make sure SDA line goes back HIGH again */
+		udelay(5);
+	}
+
+	/* clear any flags set */
+	riic_writeb(riic, 0, RIIC_ICSR2);
+	/* read back register to confirm writes */
+	riic_readb(riic, RIIC_ICSR2);
+
+	/* restore back ICFER_MALE */
+	riic_clear_set_bit(riic, 0, ICFER_MALE, RIIC_ICFER);
+
+	if (!(riic_readb(riic, RIIC_ICCR1) & ICCR1_SDAI) ||
+	    !(riic_readb(riic, RIIC_ICCR1) & ICCR1_SCLI))
+		return -EINVAL;
+
 	return 0;
 }
 
@@ -447,6 +522,10 @@ static const struct riic_irq_desc riic_irqs[] = {
 	{ .res_num = 5, .isr = riic_tend_isr, .name = "riic-nack" },
 };
 
+static struct i2c_bus_recovery_info riic_bri = {
+	.recover_bus = riic_recover_bus,
+};
+
 static int riic_i2c_probe(struct platform_device *pdev)
 {
 	struct device *dev = &pdev->dev;
@@ -491,6 +570,7 @@ static int riic_i2c_probe(struct platform_device *pdev)
 	strscpy(adap->name, "Renesas RIIC adapter", sizeof(adap->name));
 	adap->owner = THIS_MODULE;
 	adap->algo = &riic_algo;
+	adap->bus_recovery_info = &riic_bri;
 	adap->dev.parent = dev;
 	adap->dev.of_node = dev->of_node;
 
@@ -503,7 +583,7 @@ static int riic_i2c_probe(struct platform_device *pdev)
 	pm_runtime_use_autosuspend(dev);
 	pm_runtime_enable(dev);
 
-	ret = riic_init_hw(riic);
+	ret = riic_init_hw(riic, false);
 	if (ret)
 		goto out;
 
@@ -611,7 +691,7 @@ static int riic_i2c_resume(struct device *dev)
 	if (ret)
 		return ret;
 
-	ret = riic_init_hw(riic);
+	ret = riic_init_hw(riic, false);
 	if (ret) {
 		/*
 		 * In case this happens there is no way to recover from this
-- 
2.43.0





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