Commit c7b514ec authored by Wolfram Sang's avatar Wolfram Sang Committed by Wolfram Sang
Browse files

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: default avatarWolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: default avatarNiklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Signed-off-by: default avatarWolfram Sang <wsa@kernel.org>
parent 357ee884

drivers/i2c/busses/i2c-rcar.c

+4 −7
Original line number Diff line number Diff line
@@ -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);