Re: [PATCH] I2C: mpc: insert DR read in i2c_fixup()

Wolfram Sang
2014-06-02T16:27:20Z

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On Fri, May 16, 2014 at 03:36:38PM +0200, Valentin Longchamp wrote:
> The mpc_i2c_fixup function is called when the bus is not released by a
> slave. The function generates 9 pulses that should lead the slave
> to release the bus.
>
> The sequence that generates the pulses disables/enables the I2C module
> that controls the blocked bus. We have found out on the P2041 SoC that
> this could cause the CPU to hang (for a short delay).
>
> To avoid this, this patch introduces a read to the I2CDR register
> between the re-enablement of the I2C module in master mode and its
> returning to the slave mode instead of the delay (the final delay,
> between the pulses is kept), as proposed in procedure from the P2041
> reference manual (16.6.2.3).
>
> Signed-off-by: Rainer Boschung <rainer.boschung-SkAbAL50j+5BDgjK7y7TUQ@public.gmane.org>
> Signed-off-by: Valentin Longchamp <valentin.longchamp-SkAbAL50j+5BDgjK7y7TUQ@public.gmane.org>

Have you checked other manuals if this always has been the proposed
procedure?

> ---
>
> drivers/i2c/busses/i2c-mpc.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/i2c/busses/i2c-mpc.c b/drivers/i2c/busses/i2c-mpc.c
> index f539163..3655af7 100644
> --- a/drivers/i2c/busses/i2c-mpc.c
> +++ b/drivers/i2c/busses/i2c-mpc.c
> @@ -107,6 +107,7 @@ static irqreturn_t mpc_i2c_isr(int irq, void *dev_id)
> static void mpc_i2c_fixup(struct mpc_i2c *i2c)
> {
> int k;
> + u8 dr;

Looks like we can drop this variable since the value read is not used?

> u32 delay_val = 1000000 / i2c->real_clk + 1;
>
> if (delay_val < 2)
> @@ -115,7 +116,7 @@ static void mpc_i2c_fixup(struct mpc_i2c *i2c)
> for (k = 9; k; k--) {
> writeccr(i2c, 0);
> writeccr(i2c, CCR_MSTA | CCR_MTX | CCR_MEN);
> - udelay(delay_val);
> + dr = readb(i2c->base + MPC_I2C_DR);
> writeccr(i2c, CCR_MEN);
> udelay(delay_val << 1);
> }
> --
> 1.8.0.1
>

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