[patch 1/9] efikamx: read board id

[Matt Sealey]

Very few parts of the system require the board id pins to work out the
version. It would be better if the IOMUX was set up and then anything
that requires a flipflop on the board revision is done last. We do
that in the EfikaMX kernels - SDHC and a couple other things rely on
board id but the vast majority of other things (SPI etc.) absolutely
do not.

The time it takes to perform the init of 1 or 2 other units via IOMUX
is time enough to let the PCB id pins settle. This is one of the
reasons we split our board support in our kernels into seperate
files..

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



On Wed, Oct 20, 2010 at 3:24 AM, Sascha Hauer <s.hauer at pengutronix.de> wrote:
> 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).
>
> Maybe it's possible to delay only the registering of the devices which
> depend on the board revision, perhaps with a workqueue. But ok, I don't
> care much and this won't be a show stopper for this patch.
>
>
> --
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