[U-Boot] [PATCH] mx6: Add IOMUX_CONFIG_SION flag to all GPIO pins

[Eric Nelson <eric.nelson@boundarydevices.com>]

Hi Stefano,

On 10/01/2013 09:10 AM, Stefano Babic wrote:
> Hi Eric,
>
> On 01/10/2013 17:56, Eric Nelson wrote:
>> Hi Stefano,
>>
>> On 10/01/2013 07:49 AM, Stefano Babic wrote:
>>> Hi Eric,
>>>
>>> On 01/10/2013 16:26, Eric Nelson wrote:
>>>
>>>> I'm not sure where you're seeing this in the RM, but in
>>>> order to read the pad state when not configured as an input,
>>>> the SION bit needs to be set in the pad mux register on i.MX51/53.
>>>
>>> I have checked inside the "37.3.2.2 GPIO Write" for i.MX53 and "
>>> 35.4.2.1 Read Value from Pad" for i:MX51, I have not read anything about
>>> SION. If someone has found where it is described, please mail !
>>>
>>
>> That documentation seems to imply that there's no dependency
>> (i.e. there's no reference to SION), but I think that's an omission.
>
> Ok - this is surely not the first time we find errors in the documentation.
>
>> I've tested this many times, since it's a really handy way of
>> debugging hardware setups.
>>
>> That said, I'm not sure that there's a huge difference between
>> a single patch or multiple patches for each arch unless there's
>> some functionality dependent on being able to read the actual
>> value of a pin configured as a GPIO output.
>
> Ok - then I tend to apply Otavio's patch, and we will fix for the other
> i.MXes if we really find the same issues.
>
>>
>> Did I miss something in this thread that does actually require
>> that ability? It seems a pretty obscure thing in the normal case
>> to drive an output without confidence that it will succeed.
>
> Yes, it seems quite strange, but it helps to debug the hardware. It is
> not the first time we see that, even driving the output, the signal does
> not go to the expected value, due for example to a conflict (another
> peripheral driving the signal) or to a wrong pull up resistor. As U-Boot
> is a great tool for hardware debugging, reading the signal back let
> check that the output is set to the desired value.
>

I agree with all of that, though this only covers the case of a
pin set up as a GPIO output, and that same debugging approach
is often used for other functions (display data pins, clock inputs
and outputs, et cetera).

You probably wouldn't just set SION on all pins, right? I suspect
that there'd be some ramification in terms of power consumption if
nothing else.

Regards,


Eric