[patch 1/9] efikamx: read board id

[Matt Sealey]

Uwe, there is no way to tell if the pads have settled, it is entirely
a hardware problem, just like when GPIOs are at random input states if
they are not connected to anything: in this case, first of all the
IOMUX pull downs and then the GPIO change to input takes longer than
you can safely do it and then immediately read the pins or board
version 1.1 and below will not ID correctly.

-- 
Matt Sealey <matt at genesi-usa.com>
Product Development Analyst, Genesi USA, Inc.



2010/10/20 Uwe Kleine-König <u.kleine-koenig at pengutronix.de>:
> Hiho,
>
> On Tue, Oct 19, 2010 at 04:30:25PM -0500, Matt Sealey wrote:
>> On Tue, Oct 19, 2010 at 4:15 PM, Sascha Hauer <s.hauer at pengutronix.de> wrote:
>> > On Tue, Oct 19, 2010 at 10:42:54PM +0200, Arnaud Patard wrote:
>> >> read board id value from the GPIO3_16/17/11
>> >>
>> >>
>> >> +/*   PCBID2  PCBID1 PCBID0  STATE
>> >> +     1       1      1    ER1:rev1.1
>> >> +     1       1      0    ER2:rev1.2
>> >> +     1       0      1    ER3:rev1.3
>> >> +     1       0      0    ER4:rev1.4
>> >> +*/
>> >> +static void __init mx51_efikamx_board_id(void)
>> >> +{
>> >> +     int id;
>> >> +
>> >> +     /* things are taking time to settle */
>> >> +     msleep(500);
>> >
>> > Is it really necessary to delay the boot process such a long time?
>>
>> Yes. On older boards the PCBID pins are pulled high by IOMUX settings
>> (a pulldown on the board on newer revisions will keep it down). IOMUX
>> and GPIO stuff takes a little while to settle in, so if you do it
>> immediately, it will return some freakish values based on random GPIO
>> setup (it may be high, low, or none of the above at any point before
>> the pad setting kicks in).
> If the bootloader might configure the pins correctly, maybe something
> like:
>
>        if (pins_are_not_yet_configured_correctly()) {
>                do_configure_them();
>                msleep(500);
>        }
>
> ?
>
> Best regards
> Uwe
>
>
> --
> Pengutronix e.K.                           | Uwe Kleine-König            |
> Industrial Linux Solutions                 | http://www.pengutronix.de/  |
>