linux-kernel - [PATCH v2 2/3] i2c: cadence: Set the hardware time-out register to maximum value

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Date:	Wed,  3 Dec 2014 18:05:25 +0530
From:	Harini Katakam <harinik@...inx.com>
To:	wsa@...-dreams.de, mark.rutland@....com
Cc:	michal.simek@...inx.com, soren.brinkmann@...inx.com,
	linux-arm-kernel@...ts.infradead.org, linux-i2c@...r.kernel.org,
	linux-kernel@...r.kernel.org, vishnum@...inx.com,
	harinik@...inx.com, harinikatakamlinux@...il.com
Subject: [PATCH v2 2/3] i2c: cadence: Set the hardware time-out register to maximum value

From: Vishnu Motghare <vishnum@...inx.com>

Cadence I2C controller has bug wherein it generates invalid read transactions
after timeout in master receiver mode. This driver does not use the HW
timeout and this interrupt is disabled but the feature itself cannot be
disabled. Hence, this patch writes the maximum value (0xFF) to this register.
This is one of the workarounds to this bug and it will not avoid the issue
completely but reduces the chances of error.

Signed-off-by: Vishnu Motghare <vishnum@...inx.com>
Signed-off-by: Harini Katakam <harinik@...inx.com>
---

v2:
Added comments in driver.

---
 drivers/i2c/busses/i2c-cadence.c |   11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/i2c/busses/i2c-cadence.c b/drivers/i2c/busses/i2c-cadence.c
index e54899e..67077c2 100644
--- a/drivers/i2c/busses/i2c-cadence.c
+++ b/drivers/i2c/busses/i2c-cadence.c
@@ -111,6 +111,8 @@
 #define CDNS_I2C_DIVA_MAX	4
 #define CDNS_I2C_DIVB_MAX	64
 
+#define CDNS_I2C_TIMEOUT_MAX	0xFF
+
 #define cdns_i2c_readreg(offset)       readl_relaxed(id->membase + offset)
 #define cdns_i2c_writereg(val, offset) writel_relaxed(val, id->membase + offset)
 
@@ -858,6 +860,15 @@ static int cdns_i2c_probe(struct platform_device *pdev)
 		goto err_clk_dis;
 	}
 
+	/*
+	 * Cadence I2C controller has a bug wherein it generates
+	 * invalid read transaction after HW timeout in master receiver mode.
+	 * HW timeout is not used by this driver and the interrupt is disabled.
+	 * But the feature itself cannot be disabled. Hence maximum value
+	 * is written to this register to reduce the chances of error.
+	 */
+	cdns_i2c_writereg(CDNS_I2C_TIMEOUT_MAX, CDNS_I2C_TIME_OUT_OFFSET);
+
 	dev_info(&pdev->dev, "%u kHz mmio %08lx irq %d\n",
 		 id->i2c_clk / 1000, (unsigned long)r_mem->start, id->irq);
 
-- 
1.7.9.5

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