linux-kernel - [PATCH] i2c: aspeed: Acknowledge most interrupts early in interrupt handler

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Date:   Thu, 13 Sep 2018 20:30:10 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Brendan Higgins <brendanhiggins@...gle.com>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Joel Stanley <joel@....id.au>,
        Andrew Jeffery <andrew@...id.au>, linux-i2c@...r.kernel.org,
        openbmc@...ts.ozlabs.org, linux-aspeed@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org,
        Cédric Le Goater <clg@...d.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Jae Hyun Yoo <jae.hyun.yoo@...ux.intel.com>
Subject: [PATCH] i2c: aspeed: Acknowledge most interrupts early in interrupt handler

Commit 3e9efc3299dd ("i2c: aspeed: Handle master/slave combined irq events
properly") moved interrupt acknowledgment to the end of the interrupt
handler. In part this was done because the AST2500 datasheet says:

 I2CD10 Interrupt Status Register
   bit 2 Receive Done Interrupt status
         S/W needs to clear this status bit to allow next data receiving.

Acknowledging Receive Done before receive data was handled resulted in
receive errors on high speed I2C busses.

However, interrupt acknowledgment was not only moved to the end of the
interrupt handler for Receive Done Interrupt status, but for all interrupt
status bits. This could result in race conditions if a second interrupt was
received during interrupt handling and not handled but still acknowledged
at the end of the interrupt handler.

Acknowledge only "Receive Done Interrupt status" late in the interrupt
handler to solve the problem.

Fixes: 3e9efc3299dd ("i2c: aspeed: Handle master/slave combined irq events properly")
Cc: Jae Hyun Yoo <jae.hyun.yoo@...ux.intel.com>
Cc: Joel Stanley <joel@....id.au>
Signed-off-by: Guenter Roeck <linux@...ck-us.net>
---
 drivers/i2c/busses/i2c-aspeed.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/i2c/busses/i2c-aspeed.c b/drivers/i2c/busses/i2c-aspeed.c
index c258c4d9a4c0..3d518e09369f 100644
--- a/drivers/i2c/busses/i2c-aspeed.c
+++ b/drivers/i2c/busses/i2c-aspeed.c
@@ -552,6 +552,9 @@ static irqreturn_t aspeed_i2c_bus_irq(int irq, void *dev_id)
 
 	spin_lock(&bus->lock);
 	irq_received = readl(bus->base + ASPEED_I2C_INTR_STS_REG);
+	/* Ack all interrupts except for Rx done */
+	writel(irq_received & ~ASPEED_I2CD_INTR_RX_DONE,
+	       bus->base + ASPEED_I2C_INTR_STS_REG);
 	irq_remaining = irq_received;
 
 #if IS_ENABLED(CONFIG_I2C_SLAVE)
@@ -584,8 +587,10 @@ static irqreturn_t aspeed_i2c_bus_irq(int irq, void *dev_id)
 			"irq handled != irq. expected 0x%08x, but was 0x%08x\n",
 			irq_received, irq_handled);
 
-	/* Ack all interrupt bits. */
-	writel(irq_received, bus->base + ASPEED_I2C_INTR_STS_REG);
+	/* Ack Rx done */
+	if (irq_received & ASPEED_I2CD_INTR_RX_DONE)
+		writel(ASPEED_I2CD_INTR_RX_DONE,
+		       bus->base + ASPEED_I2C_INTR_STS_REG);
 	spin_unlock(&bus->lock);
 	return irq_remaining ? IRQ_NONE : IRQ_HANDLED;
 }
-- 
2.7.4