i2c: rcar: faster irq code to minimize HW race condition

To avoid the HW race condition on R-Car Gen2 and earlier, we need to
write to ICMCR as soon as possible in the interrupt handler. We can
improve this by writing a static value instead of masking out bits.
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Signed-off-by: Wolfram Sang <wsa@kernel.org>

drivers/i2c/busses/i2c-rcar.c

@@ -91,7 +91,6 @@
 
 #define RCAR_BUS_PHASE_START	(MDBS | MIE | ESG)
 #define RCAR_BUS_PHASE_DATA	(MDBS | MIE)
-#define RCAR_BUS_MASK_DATA	(~(ESG | FSB) & 0xFF)
 #define RCAR_BUS_PHASE_STOP	(MDBS | MIE | FSB)
 
 #define RCAR_IRQ_SEND	(MNR | MAL | MST | MAT | MDE)
@@ -621,7 +620,7 @@ static bool rcar_i2c_slave_irq(struct rcar_i2c_priv *priv)
 /*
  * This driver has a lock-free design because there are IP cores (at least
  * R-Car Gen2) which have an inherent race condition in their hardware design.
- * There, we need to clear RCAR_BUS_MASK_DATA bits as soon as possible after
+ * There, we need to switch to RCAR_BUS_PHASE_DATA as soon as possible after
  * the interrupt was generated, otherwise an unwanted repeated message gets
  * generated. It turned out that taking a spinlock at the beginning of the ISR
  * was already causing repeated messages. Thus, this driver was converted to
@@ -630,13 +629,11 @@ static bool rcar_i2c_slave_irq(struct rcar_i2c_priv *priv)
 static irqreturn_t rcar_i2c_irq(int irq, void *ptr)
 {
 	struct rcar_i2c_priv *priv = ptr;
-	u32 msr, val;
+	u32 msr;
 
 	/* Clear START or STOP immediately, except for REPSTART after read */
-	if (likely(!(priv->flags & ID_P_REP_AFTER_RD))) {
-		val = rcar_i2c_read(priv, ICMCR);
-		rcar_i2c_write(priv, ICMCR, val & RCAR_BUS_MASK_DATA);
-	}
+	if (likely(!(priv->flags & ID_P_REP_AFTER_RD)))
+		rcar_i2c_write(priv, ICMCR, RCAR_BUS_PHASE_DATA);
 
 	msr = rcar_i2c_read(priv, ICMSR);