Re: [PATCH] OMAP3: I2C: Errata i207: Clear wrong RDR interrupt

[Nishanth Menon <nm-l0cyMroinI0@public.gmane.org>]

G, Manjunath Kondaiah had written, on 04/01/2010 07:20 AM, the following:
> Under certain rare conditions, I2C_STAT[13].RDR bit may be set
> and the corresponding interrupt fire, even there is no data in
> the receive FIFO, or the I2C data transfer is still ongoing.
> These spurious RDR events must be ignored by the software.
> 
> This patch handles and ignores RDR spurious interrupts.
> 
> Reviewed-by: Kalliguddi, Hema <hemahk-l0cyMroinI0@public.gmane.org>
> Signed-off-by: Manjunatha GK <manjugk-l0cyMroinI0@public.gmane.org>
> Cc: linux-omap-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
> Cc: linux-i2c-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
> Cc: ben-linux-elnMNo+KYs3YtjvyW6yDsg@public.gmane.org
> Cc: Kalliguddi, Hema <hemahk-l0cyMroinI0@public.gmane.org>
> ---
>  drivers/i2c/busses/i2c-omap.c |   13 +++++++++++++
>  1 files changed, 13 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-omap.c b/drivers/i2c/busses/i2c-omap.c
> index f2019d2..acf4076 100644
> --- a/drivers/i2c/busses/i2c-omap.c
> +++ b/drivers/i2c/busses/i2c-omap.c
> @@ -796,6 +796,19 @@ complete:
>  		}
>  		if (stat & (OMAP_I2C_STAT_RRDY | OMAP_I2C_STAT_RDR)) {
>  			u8 num_bytes = 1;
> +
> +			/*
> +			 * OMAP3 I2C Errata ID: i207
> +			 * Under certain rare conditions, RDR could be set again
> +			 * when the bus is busy, then clear and ignore the interrupt
> +			 */
> +			if (!(stat & OMAP_I2C_STAT_RRDY) && (stat &
> +						OMAP_I2C_STAT_BB)) {
> +				/* clear RDR */
> +				omap_i2c_ack_stat(dev, stat & OMAP_I2C_STAT_RDR);
> +				dev_err(dev->dev, "I2C: RDR when bus is busy.\n");
> +				return IRQ_HANDLED;
> +			}
couple of comments after reading thru the errata:
a) the sequence in the errata doc is:
if (stat & OMAP_I2C_STAT_RDR) { /* This is cleaner that using an obtuse 
check using !(stat & OMAP_I2C_STAT_RRDY) */
	omap_i2c_ack_stat(dev, stat & OMAP_I2C_STAT_RDR); /* dummy read - i 
think this needs clarification as to why */
	if (omap_i2c_read_reg(dev, OMAP_I2C_STAT_REG) & OMAP_I2C_STAT_BB) /* 
reason for the i2c_read_reg is because errata mentions a dummy stat read 
  which might mean something for BB -> I am not sure may need to be 
checked with H/w team. */
		continue; /* recheck - faster response compared to return and re 
generate interrupt */
}


b) does this apply to  OMAP2 and OMAP4?

(unrelated sidenote: my usual crib: we probably need an errata 
management system soon considering the erratas that are getting 
workedaround  in code.. :( )..
>  			if (dev->fifo_size) {
>  				if (stat & OMAP_I2C_STAT_RRDY)
>  					num_bytes = dev->fifo_size;


-- 
Regards,
Nishanth Menon