Subject: Re: [PATCH/RFC 1/2] 5200: improve i2c bus error recovery

From: "Albrecht Dreß" <[email-masked]>
Date: Tue, 16 Feb 2010 21:14:00 +0100 (CET)

Hi Ira:

[snip]
> I see this exact hang on a MPC8349EA board. I poll my i2c sensors every
> 500ms, and it takes around 12 hours to produce a hang. The usual hang
> has (CF | BB) set, however I have seen a hang with just BB (only once so
> far in about 2 weeks).
> 
> I think the fixup should be run on 8349 as well, if not all processors.
> I'm happy to test patches. I have a way to reliably trigger a lockup,
> using another master on the i2c bus.

See my other post - hopefully a new patch is ready tomorrow/Thursday...

[snip]
> >  static void mpc_i2c_fixup(struct mpc_i2c *i2c)
> >  {
> > -	writeccr(i2c, 0);
> > -	udelay(30);
> > -	writeccr(i2c, CCR_MEN);
> > -	udelay(30);
> > -	writeccr(i2c, CCR_MSTA | CCR_MTX);
> > -	udelay(30);
> > -	writeccr(i2c, CCR_MSTA | CCR_MTX | CCR_MEN);
> > -	udelay(30);
> > -	writeccr(i2c, CCR_MEN);
> > -	udelay(30);
> > +	if (i2c->real_clk == 0) {
> > +		writeccr(i2c, 0);
> > +		udelay(30);
> > +		writeccr(i2c, CCR_MEN);
> > +		udelay(30);
> > +		writeccr(i2c, CCR_MSTA | CCR_MTX);
> > +		udelay(30);
> > +		writeccr(i2c, CCR_MSTA | CCR_MTX | CCR_MEN);
> > +		udelay(30);
> > +		writeccr(i2c, CCR_MEN);
> > +		udelay(30);
> > +	} else {
> > +		int k;
> > +		u32 delay_val = 1000000 / i2c->real_clk + 1;
> > +
> > +		if (delay_val < 2)
> > +			delay_val = 2;
> > +
> > +		for (k = 9; k; k--) {
> > +			writeccr(i2c, 0);
> > +			writeccr(i2c, CCR_MSTA | CCR_MTX | CCR_MEN);
> > +			udelay(delay_val);
> > +			writeccr(i2c, CCR_MEN);
> > +			udelay(delay_val << 1);
> > +		}
> > +	}
> >  }
> >  
> 
> The old sequence has always un-hung the bus for me. Yours might be
> better. I'll try it next time the bus wedges up on me.

The easiest way to verify the /waveforms/ is to simply call the function somewhere else (e.g. in a i2c write call), and then record SCK and SDA with a scope.  I saw *huge* unnecessary delays in the original code, and by some creative interpretation of the (not very clear) 5200 data sheet I came to the write's and delays above.  If you have a scope, you might want to repeat the test with your '8349.

Best, Albrecht.

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