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From: Kumar Gala <galak@kernel.crashing.org>
To: Fredrik Arnerup <fredrik.arnerup@edgeware.tv>
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Subject: Re: MPC85xx erratum "I2C1 - I2C controller is unable to generate
	clocks when SDA is low coming out of reset"
Date: Wed, 10 Jun 2009 23:32:13 -0500
References: <738D541FBC1741A18DB4F3CB466DF78A@edgeware.tv>
Cc: linuxppc-dev@ozlabs.org
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On May 26, 2009, at 3:22 AM, Fredrik Arnerup wrote:

> We've had some trouble with I2C not working after a soft reboot,
> which we think is due to the the erratum "I2C1" which is present in
> at least the mpc8540 and the mpc8560. Since there is no good  
> workaround,
> the only choice seems to be to avoid resetting the CPU while the I2C  
> bus is
> busy.
>
> The problem seems to be that the i2c-mpc driver leaves I2C in a busy  
> state
> when
> it receives a signal (e.g. upon shutdown).
> The code below is not meant as a patch, just me thinking aloud.
> Thoughts?
>
> /Fredrik Arnerup
> fredrik.arnerup@edgeware.tv
>
> Index: drivers/i2c/busses/i2c-mpc.c
> ===================================================================
> --- drivers/i2c/busses/i2c-mpc.c        (revision 6933)
> +++ drivers/i2c/busses/i2c-mpc.c        (working copy)
> @@ -262,12 +262,14 @@
>        /* Allow bus up to 1s to become not busy */
>        while (readb(i2c->base + MPC_I2C_SR) & CSR_MBB) {
>                if (signal_pending(current)) {
> -                       pr_debug("I2C: Interrupted\n");
> -                       writeccr(i2c, 0);
> +                       printk(KERN_WARNING "I2C: Interrupted\n");
> +                       if (readb(i2c->base + MPC_I2C_SR) ==
> +                           (CSR_MCF | CSR_MBB | CSR_RXAK))
> +                               mpc_i2c_fixup(i2c);
>                        return -EINTR;
>                }
>                if (time_after(jiffies, orig_jiffies + HZ)) {
> -                       pr_debug("I2C: timeout\n");
> +                       printk(KERN_WARNING "I2C: mpc_xfer() timeout 
> \n");
>                        if (readb(i2c->base + MPC_I2C_SR) ==
>                            (CSR_MCF | CSR_MBB | CSR_RXAK))
>                                mpc_i2c_fixup(i2c);


I don't think we should have the printk's.  Its possible that we hit  
the interrupted condition while using the i2c from user space.

- k