[PATCH V2] staging: nvec: make i2c controller register writes robust

[Marc Dietrich <marvin24@xxxxxx>]

The i2c controller needs to read back the data written to its registers.
This way we can avoid the long delay in the interrupt handler.

Signed-off-by: Marc Dietrich <marvin24@xxxxxx>
---
V2: rename i2c_writel to tegra_i2c_writel
 drivers/staging/nvec/nvec.c | 41 ++++++++++++++++++++++---------------
 1 file changed, 24 insertions(+), 17 deletions(-)

diff --git a/drivers/staging/nvec/nvec.c b/drivers/staging/nvec/nvec.c
index e5ca78e57384..d67d2f3338b2 100644
--- a/drivers/staging/nvec/nvec.c
+++ b/drivers/staging/nvec/nvec.c
@@ -570,6 +570,22 @@ static void nvec_tx_set(struct nvec_chip *nvec)
 		(uint)nvec->tx->size, nvec->tx->data[1]);
 }

+/**
+ * tegra_i2c_writel - safely write to an I2C client controller register
+ * @val: value to be written
+ * @reg: register to write to
+ *
+ * A write to an I2C controller register needs to be read back to make sure
+ * that the value has arrived.
+ */
+static void tegra_i2c_writel(u32 val, void *reg)
+{
+	writel_relaxed(val, reg);
+
+	/* read back register to make sure that register writes completed */
+	readl_relaxed(reg);
+}
+
 /**
  * nvec_interrupt - Interrupt handler
  * @irq: The IRQ
@@ -604,7 +620,7 @@ static irqreturn_t nvec_interrupt(int irq, void *dev)
 	if ((status & RNW) == 0) {
 		received = readl(nvec->base + I2C_SL_RCVD);
 		if (status & RCVD)
-			writel(0, nvec->base + I2C_SL_RCVD);
+			tegra_i2c_writel(0, nvec->base + I2C_SL_RCVD);
 	}

 	if (status == (I2C_SL_IRQ | RCVD))
@@ -696,7 +712,7 @@ static irqreturn_t nvec_interrupt(int irq, void *dev)

 	/* Send data if requested, but not on end of transmission */
 	if ((status & (RNW | END_TRANS)) == RNW)
-		writel(to_send, nvec->base + I2C_SL_RCVD);
+		tegra_i2c_writel(to_send, nvec->base + I2C_SL_RCVD);

 	/* If we have send the first byte */
 	if (status == (I2C_SL_IRQ | RNW | RCVD))
@@ -713,15 +729,6 @@ static irqreturn_t nvec_interrupt(int irq, void *dev)
 		status & RCVD ? " RCVD" : "",
 		status & RNW ? " RNW" : "");

-	/*
-	 * TODO: replace the udelay with a read back after each writel above
-	 * in order to work around a hardware issue, see i2c-tegra.c
-	 *
-	 * Unfortunately, this change causes an initialisation issue with the
-	 * touchpad, which needs to be fixed first.
-	 */
-	udelay(100);
-
 	return IRQ_HANDLED;
 }

@@ -737,15 +744,15 @@ static void tegra_init_i2c_slave(struct nvec_chip *nvec)

 	val = I2C_CNFG_NEW_MASTER_SFM | I2C_CNFG_PACKET_MODE_EN |
 	    (0x2 << I2C_CNFG_DEBOUNCE_CNT_SHIFT);
-	writel(val, nvec->base + I2C_CNFG);
+	tegra_i2c_writel(val, nvec->base + I2C_CNFG);

 	clk_set_rate(nvec->i2c_clk, 8 * 80000);

-	writel(I2C_SL_NEWSL, nvec->base + I2C_SL_CNFG);
-	writel(0x1E, nvec->base + I2C_SL_DELAY_COUNT);
+	tegra_i2c_writel(I2C_SL_NEWSL, nvec->base + I2C_SL_CNFG);
+	tegra_i2c_writel(0x1E, nvec->base + I2C_SL_DELAY_COUNT);

-	writel(nvec->i2c_addr >> 1, nvec->base + I2C_SL_ADDR1);
-	writel(0, nvec->base + I2C_SL_ADDR2);
+	tegra_i2c_writel(nvec->i2c_addr >> 1, nvec->base + I2C_SL_ADDR1);
+	tegra_i2c_writel(0, nvec->base + I2C_SL_ADDR2);

 	enable_irq(nvec->irq);
 }
@@ -754,7 +761,7 @@ static void tegra_init_i2c_slave(struct nvec_chip *nvec)
 static void nvec_disable_i2c_slave(struct nvec_chip *nvec)
 {
 	disable_irq(nvec->irq);
-	writel(I2C_SL_NEWSL | I2C_SL_NACK, nvec->base + I2C_SL_CNFG);
+	tegra_i2c_writel(I2C_SL_NEWSL | I2C_SL_NACK, nvec->base + I2C_SL_CNFG);
 	clk_disable_unprepare(nvec->i2c_clk);
 }
 #endif
--
2.43.0