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

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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>
This commit is contained in:
Wolfram Sang 2020-12-23 18:21:51 +01:00 committed by Wolfram Sang
parent 357ee8841d
commit c7b514ec97
1 changed files with 4 additions and 7 deletions
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11
drivers/i2c/busses/i2c-rcar.c
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@ -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);