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+Date: Tue, 15 Jul 2008 13:00:18 -0600 (MDT)
+From: Paul Walmsley <paul@pwsan.com>
+To: linux-omap@vger.kernel.org
+Subject: [PATCH] i2c-omap: close suspected race between omap_i2c_idle() and
+ omap_i2c_isr()
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+
+
+omap_i2c_idle() sets an internal flag, "dev->idle", instructing its
+ISR to decline interrupts. It sets this flag before it actually masks
+the interrupts on the I2C controller. This is problematic, since an
+I2C interrupt could arrive after dev->idle is set, but before the
+interrupt source is masked. When this happens, Linux disables the I2C
+controller's IRQ, causing all future transactions on the bus to fail.
+
+Symptoms, happening on about 7% of boots:
+
+ irq 56: nobody cared (try booting with the "irqpoll" option)
+ <warning traceback here>
+ Disabling IRQ #56
+ i2c_omap i2c_omap.1: controller timed out
+
+In omap_i2c_idle(), this patch sets dev->idle only after the interrupt
+mask write to the I2C controller has left the ARM write buffer.
+That's probably the major offender. For additional prophylaxis, in
+omap_i2c_unidle(), the patch clears the dev->idle flag before
+interrupts are enabled, rather than afterwards.
+
+The patch has survived twenty-two reboots on the 3430SDP here without
+wedging I2C1. Not absolutely dispositive, but promising!
+
+
+Signed-off-by: Paul Walmsley <paul@pwsan.com>
+---
+
+ drivers/i2c/busses/i2c-omap.c | 10 ++++++++--
+ 1 files changed, 8 insertions(+), 2 deletions(-)
+
+diff --git a/drivers/i2c/busses/i2c-omap.c b/drivers/i2c/busses/i2c-omap.c
+index 55779f5..ed7e9ad 100644
+--- a/drivers/i2c/busses/i2c-omap.c
++++ b/drivers/i2c/busses/i2c-omap.c
+@@ -209,22 +209,28 @@ static void omap_i2c_unidle(struct omap_i2c_dev *dev)
+ if (dev->iclk != NULL)
+ clk_enable(dev->iclk);
+ clk_enable(dev->fclk);
++ dev->idle = 0;
+ if (dev->iestate)
+ omap_i2c_write_reg(dev, OMAP_I2C_IE_REG, dev->iestate);
+- dev->idle = 0;
+ }
+
+ static void omap_i2c_idle(struct omap_i2c_dev *dev)
+ {
+ u16 iv;
+
+- dev->idle = 1;
+ dev->iestate = omap_i2c_read_reg(dev, OMAP_I2C_IE_REG);
+ omap_i2c_write_reg(dev, OMAP_I2C_IE_REG, 0);
+ if (dev->rev1)
+ iv = omap_i2c_read_reg(dev, OMAP_I2C_IV_REG);
+ else
+ omap_i2c_write_reg(dev, OMAP_I2C_STAT_REG, dev->iestate);
++ /*
++ * The wmb() is to ensure that the I2C interrupt mask write
++ * reaches the I2C controller before the dev->idle store
++ * occurs.
++ */
++ wmb();
++ dev->idle = 1;
+ clk_disable(dev->fclk);
+ if (dev->iclk != NULL)
+ clk_disable(dev->iclk);
+--
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projects / vuplus_openembedded / commitdiff