Re: [PATCH v2] qe_lib: Set gpio data before changing the direction to output

[Anton Vorontsov <avorontsov@ru.mvista.com>]

On Wed, Aug 19, 2009 at 09:30:20AM -0400, Michael Barkowski wrote:
> Anton Vorontsov wrote:
> > On Tue, Aug 18, 2009 at 05:33:00PM -0500, Timur Tabi wrote:
> >> Anton Vorontsov wrote:
> >>> On Tue, Aug 18, 2009 at 05:20:44PM -0400, Michael Barkowski wrote:
> >>>> This avoids having a short glitch if the desired initial value is not
> >>>> the same as what was previously in the data register.
> >>>>
> >>>> Signed-off-by: Michael Barkowski <michaelbarkowski@ruggedcom.com>
> >>> Acked-by: Anton Vorontsov <avorontsov@ru.mvista.com>
> >> I don't have the time to test this patch, so I abstain from acking. :-)
> >> If Anton likes it, that's good enough for me.
> > 
> > You made me doubt for a moment. :-) Thanks for the suspiciousness.
> > 
> > What happens if a pin was previously configured as input? Does our
> > write to the data register survive? For MPC8xxx GPIO controllers
> > it does. And randomly taken QE spec says:
> > 
> >   A write to CPDAT is latched, and if the corresponding CPDIR
> >   bits have configured the port pin as an output, the latched
> >   value is driven onto the respective pin. However, if the
> >   corresponding CPDIR bits have configured the port pin as an
> >   input, the latched value is prevented from reaching the pin.
> > 
> > I guess we're safe, but Michael, could you actually test it
> > (if not already)?
> > 
> 
> I had tested it before with the pin initially configured as "disabled".
> 
> I have now also tested it with the pin initially configured as "input".
> 
> The value written to CPDAT seems to survive and is driven onto the pin
> once CPDIR is changed to 1, just as noted in the spec.
> 
> Tested on 8360, by probing with a logic analyzer.

Great, thanks a lot! I think the patch is perfect.

-- 
Anton Vorontsov
email: cbouatmailru@gmail.com
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