Query on direction_output fn of PL061 GPIO driver.
Viresh KUMAR
viresh.kumar at st.com
Tue Apr 13 07:40:41 EDT 2010
On 4/13/2010 5:02 PM, Baruch Siach wrote:
>> > In current implementation, firstly value of GPIO pin is modified and then its
>> > direction is set to OUT. In our SOCs (ST SPEAr), this implementation doesn't
>> > work correctly (we have pl061 in our soc). Suppose previously pin is in IN mode,
>> > now writing val to it doesn't change anything because it is in IN mode and we
>> > can write to a pin only when it is in OUT mode. Now if its direction is
>> > changed to OUT then also its value will remain same and will not be changed to
>> > what we wanted.
>> >
>> > Am i missing something?
> Probably not. This is a design bug in the PL061 hardware. Changing the
> direction before the value makes the output value of the GPIO undefined
> (apparently 0) for a short period of time. This is bad news for some
> applications.
>
thanks for your prompt reply.
Ok. so this may cause problem on the board.
Anyway if this is the issue, then writing value to val register has no effects.
> Anyway, the right thing to do here is to reverse do just that, since the
> current way of doing things is broken.
I didn't get it completely. If i got it correctly, maybe myself or you can just
send a patch to reverse this, i.e. writing val and setting direction.
Am i correct?
regards,
viresh kumar.
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