On Thu, Nov 29, 2012 at 10:35:34AM +0530, Naveen Krishna Chatradhi wrote:
> From: Simon Glass <sjg@xxxxxxxxxxxx>
>
> There is a rather odd feature of the exynos i2c controller that if it
> is left enabled, it can lock itself up with the clk line held low.
> This makes the bus unusable.
>
> Unfortunately, the s3c24xx_i2c_set_master() function does not notice
> this, and reports a timeout. From then on the bus cannot be used until
> the AP is rebooted.
>
> The problem happens when any sort of interrupt occurs (e.g. due to a
> bus transition) when we are not in the middle of a transaction. We
> have seen many instances of this when U-Boot leaves the bus apparently
> happy, but Linux cannot access it.
>
> The current code is therefore pretty fragile.
>
> This fixes things by leaving the bus disabled unless we are actually
> in a transaction. We enable the bus at the start of the transaction and
> disable it at the end. That way we won't get interrupts and will not
> lock up the bus.
>
> It might be possible to clear pending interrupts on start-up, but this
> seems to be a more robust solution. We can't service interrupts when
> we are not in a transaction, and anyway would rather not lock up the
> bus while we try.
>
> Signed-off-by: Simon Glass <sjg@xxxxxxxxxxxx>
> Cc: Grant Grundler <grundler@xxxxxxxxxxxx>
> Signed-off-by: Naveen Krishna Chatradhi <ch.naveen@xxxxxxxxxxx>
So, I assume this patch is still needed despite the ongoing discussion
about arbitration?
> ---
> drivers/i2c/busses/i2c-s3c2410.c | 37 +++++++++++++++++++++++++++++++++----
> 1 file changed, 33 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/i2c/busses/i2c-s3c2410.c b/drivers/i2c/busses/i2c-s3c2410.c
> index e93e7d6..2fd346d 100644
> --- a/drivers/i2c/busses/i2c-s3c2410.c
> +++ b/drivers/i2c/busses/i2c-s3c2410.c
> @@ -186,6 +186,31 @@ static inline void s3c24xx_i2c_enable_irq(struct s3c24xx_i2c *i2c)
> writel(tmp | S3C2410_IICCON_IRQEN, i2c->regs + S3C2410_IICCON);
> }
>
> +/*
> + * Disable the bus so that we won't get any interrupts from now on, or try
> + * to drive any lines. This is the default state when we don't have
> + * anything to send/receive.
> + *
> + * If there is an event on the bus, or we have a pre-existing event at
Otherwise, if...
> + * kernel boot time, we may not notice the event and the I2C controller
> + * will lock the bus with the I2C clock line low indefinitely.
> + */
> +static inline void s3c24xx_i2c_disable_bus(struct s3c24xx_i2c *i2c)
> +{
> + unsigned long tmp;
> +
> + /* Stop driving the I2C pins */
> + tmp = readl(i2c->regs + S3C2410_IICSTAT);
> + tmp &= ~S3C2410_IICSTAT_TXRXEN;
> + writel(tmp, i2c->regs + S3C2410_IICSTAT);
> +
> + /* We don't expect any interrupts now, and don't want send acks */
> + tmp = readl(i2c->regs + S3C2410_IICCON);
> + tmp &= ~(S3C2410_IICCON_IRQEN | S3C2410_IICCON_IRQPEND |
> + S3C2410_IICCON_ACKEN);
> + writel(tmp, i2c->regs + S3C2410_IICCON);
> +}
> +
>
> /* s3c24xx_i2c_message_start
> *
> @@ -646,7 +671,11 @@ static int s3c24xx_i2c_doxfer(struct s3c24xx_i2c *i2c,
>
> s3c24xx_i2c_wait_idle(i2c);
>
> + s3c24xx_i2c_disable_bus(i2c);
> +
> out:
> + i2c->state = STATE_IDLE;
> +
Why is the state change after the label?
> return ret;
> }
>
> @@ -912,7 +941,6 @@ static void s3c24xx_i2c_dt_gpio_free(struct s3c24xx_i2c *i2c)
>
> static int s3c24xx_i2c_init(struct s3c24xx_i2c *i2c)
> {
> - unsigned long iicon = S3C2410_IICCON_IRQEN | S3C2410_IICCON_ACKEN;
> struct s3c2410_platform_i2c *pdata;
> unsigned int freq;
>
> @@ -926,12 +954,12 @@ static int s3c24xx_i2c_init(struct s3c24xx_i2c *i2c)
>
> dev_info(i2c->dev, "slave address 0x%02x\n", pdata->slave_addr);
>
> - writel(iicon, i2c->regs + S3C2410_IICCON);
> + writel(0, i2c->regs + S3C2410_IICCON);
> + writel(0, i2c->regs + S3C2410_IICSTAT);
>
> /* we need to work out the divisors for the clock... */
>
> if (s3c24xx_i2c_clockrate(i2c, &freq) != 0) {
> - writel(0, i2c->regs + S3C2410_IICCON);
> dev_err(i2c->dev, "cannot meet bus frequency required\n");
> return -EINVAL;
> }
> @@ -939,7 +967,8 @@ static int s3c24xx_i2c_init(struct s3c24xx_i2c *i2c)
> /* todo - check that the i2c lines aren't being dragged anywhere */
>
> dev_info(i2c->dev, "bus frequency set to %d KHz\n", freq);
> - dev_dbg(i2c->dev, "S3C2410_IICCON=0x%02lx\n", iicon);
> + dev_dbg(i2c->dev, "S3C2410_IICCON=0x%02x\n",
> + readl(i2c->regs + S3C2410_IICCON));
>
Regards,
Wolfram
--
Pengutronix e.K. | Wolfram Sang |
Industrial Linux Solutions | http://www.pengutronix.de/ |
Attachment:
signature.asc
Description: Digital signature
