[RFC] power/mpc85xx: Add delay after enabling I2C master

[Scott Wood]

On 07/23/2013 10:37:46 AM, York Sun wrote:
> On 07/22/2013 05:33 PM, Scott Wood wrote:
> > On Mon, May 13, 2013 at 02:27:08PM -0700, York Sun wrote:
> >> Erratum A-006037 indicates I2C controller executes the write to  
> I2CCR only
> >> after it sees SCL idle for 64K cycle of internal I2C controller  
> clocks. If
> >> during this waiting period, I2C controller is disabled (I2CCR[MEN]  
> set to
> >> 0), then the controller could end in bad state, and hang the  
> future access
> >> to I2C register.
> >>
> >> The mpc_i2c_fixup() function tries to recover the bus from a  
> stalled state
> >> where the 9th clock pulse wasn't generated. However, this  
> workaround
> >> disables and enables I2C controller without meeting waiting  
> requirement of
> >> this erratum.
> >>
> >> This erratum applies to some 85xx SoCs. It is safe to apply to all  
> of them
> >> for mpc_i2c_fixup().
> >>
> >> Signed-off-by: York Sun <yorksun at freescale.com>
> >>
> >> ---
> >> I'd like to get rid of the #ifdef if mpc5121 is OK with the longer  
> delay.
> >
> > Are mpc5121 and mpc85xx the only things that use this?
> 
> No. 83xx and 86xx also uses this file. But I am only unsure if mpc52xx
> is OK with this extended delay. I guess they are but I don't have a
> proof, or someone to confirm.
> 
> >
> > Are you sure the delay always works out to be longer?  What is the
> > relationship between fsl_get_sys_freq() and i2c->real_clk?
> 
> Yes. The max divider from sys clock to i2c clcok is 32K.
> i2c->real_clk is the clock I2C controller pumps out, not its internal  
> operation clock.

32K is the max for all implementations?

BTW, Where does the "2000000" come from?  Shouldn't it be 1000000 if  
you're converting to usec?  If you're trying to add some slack, say so  
rather than having a comment suggest that the output of that formula is  
64K cycles.  Or is there an implicit assumption that i2c runs at half  
the system frequency?  Is that assumption true for all implementations  
that have this erratum?

> > In any case, you should send this patch to the i2c maintainer and  
> list.
> >
> 
> I don't have the name on top of my head. Is that  
> linux-i2c at vger.kernel.org?

Yes, and Wolfram Sang <wsa at the-dreams.de> is the maintainer.  This is  
listed in the MAINTAINERS file.

-Scott