On Thu, Sep 25, 2008 at 10:53:48AM +0300, Tony Lindgren wrote:
> From: Paul Walmsley <paul@xxxxxxxxx>
>
> 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!
that looks ok.
> Signed-off-by: Paul Walmsley <paul@xxxxxxxxx>
> Signed-off-by: Tony Lindgren <tony@xxxxxxxxxxx>
> ---
> 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 cfb76f5..a06ad42 100644
> --- a/drivers/i2c/busses/i2c-omap.c
> +++ b/drivers/i2c/busses/i2c-omap.c
> @@ -181,22 +181,28 @@ 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); /* Read clears */
> 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);
> --
> 1.5.6.rc3.21.g8c6b5
>
>
> _______________________________________________
> i2c mailing list
> i2c@xxxxxxxxxxxxxx
> http://lists.lm-sensors.org/mailman/listinfo/i2c
--
Ben (ben@xxxxxxxxx, http://www.fluff.org/)
'a smiley only costs 4 bytes'
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