Re: [PATCH] ARM: dts: am335x-bone* enable pmic-shutdown-controller

[Tony Lindgren <tony@atomide.com>]

* Pantelis Antoniou <pantelis.antoniou@konsulko.com> [150518 11:02]:
> Hi Tony,
> 
> > On May 18, 2015, at 20:03 , Tony Lindgren <tony@atomide.com> wrote:
> > 
> > * Robert Nelson <robertcnelson@gmail.com> [150518 09:51]:
> >> On Mon, May 18, 2015 at 11:29 AM, Tony Lindgren <tony@atomide.com> wrote:
> >>> * Robert Nelson <robertcnelson@gmail.com> [150518 09:15]:
> >>>> On Mon, May 18, 2015 at 10:21 AM, Tony Lindgren <tony@atomide.com> wrote:
> >>>> 
> >>>> All the rev information is in the board's eeprom:
> >>>> 
> >>>> hexdump -e '8/1 "%c"' /sys/bus/i2c/devices/0-0050/eeprom -s 12 -n 4
> >>>> 
> >>>> Rev A5B
> >>>> 0A5B
> >>>> 
> >>>> Rev C
> >>>> 000C
> >>>> 
> >>>> Just another default qwerk to add to Pantelis' bone_capemgr. ;)
> >>> 
> >>> It seems we should not even instantiate some devices on BBB
> >>> until the EEPROM is parsed.. So maybe something like this:
> >>> 
> >>> 1. The problem devices are initially set with status = "disabled"
> >>>   in the dts
> >>> 
> >>> 2. We set up drivers/*/bbb-eeprom.c that parses the board
> >>>   revision at module_init time, and then flips the selected
> >>>   devices to have status = "enabled" and populates the revision
> >>>   info based on the eeprom and SoC revision passed in pdata.
> >>>   Then those devices get their struct device created and
> >>>   probed, but at a much later time.
> >>> 
> >>> So rather than trying to init all that early, let's just
> >>> init them much later when we have the proper I2C driver
> >>> running?
> >> 
> >> I see that working just fine.  We (beagleboard.org) enforce the eeprom
> >> data, as all the official images require a proper baseboard eeprom.
> > 
> > OK
> > 
> >> We just have to be very careful to limit the scope, otherwise we will
> >> end up with Pantelis' rejected capebus from the v3.2.x days...
> > 
> > Naturally I was thinking #2 above would use Pantelis' code for
> > CONFIG_OF_OVERLAY in mainline. But instead of the earlier patches,
> > we can make things happen much later on to avoid the detect of
> > EEPROM early on.
> 
> Already been taken care of:
> 
> https://lkml.org/lkml/2015/2/18/258
> 
> The patchset works, but it still needs some review eyeballs.
> There might be a rename to variants or something.
> 
> You were part of that thread too :)

Right, and what I mean with #2 above is that we can make this all
into a regular drivers/* device driver with no need for the
early hacks in your series in arch/arm/mach-omap2/am33xx-dt-quirks.c.
 
> I think it’s best if we go this path instead of twiddling with the
> status properties manually. Conceptually the idea is similar to
> the detection of the white/black, with the added joy of revision
> detection.

If some device drivers depend on the I2C EEPROM, we should not
create the struct device entry for those until the I2C EEPROM
driver has parsed the EEPROM. And there's no need to do that
early, we want to do everything as late as possible. That way
we have real debug console available in most cases.
 
> Ain’t hardware designers a fun bunch or what?

We need something equal to the MS DOS boot floppy to limit their
ideas :)

Regards,

Tony
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