On 03/26/2016 01:58 AM, Iain Paton wrote:
> On 25/03/16 19:04, Michael Haas wrote:
>> This patch implements the suggested changes. It is not enough
>> to set the voltage to 2800000 to avoid the crash. Hence, I have
>> also removed regulator-always-on.
> NAK.
> If setting both min and max to 2800000 isn't working then I'd suggest you're 
> just papering over the issue and not actually solving it.
> It should be fairly clear that whenever those regulators are turned on by 
> some driver you're going to see the same issue, you've just delayed the 
> problem by removing the regulator-always-on item.
> The real problem here is people monkeying with the regulators without 
> understanding what they're doing, bothering to test the results, or caring 
> about the consequences.
> Anyway, Hans was correct in that the datasheet we have access to says that 
> the defaults for these regulators are undefined. 
> I suspect that's not the whole story though, if these regulators had random 
> values at powerup we'd have seen problems before now. 
> Most likely the values we think we know are simply incorrect plus there's 
> probably some element of sequencing involved - perhaps LDO4 needs turned on 
> first. 
> However I don't see sufficient detail in the datasheets to confirm any of 
> that, so we shouldn't assume anything.
> Electrically on the lime2 LDO3 goes to VCC-PE and LDO4 to VCC-PG. Neither 
> groups E or G appear to be connected to anything other than gpio headers, 
> so this has little to do with board design, it's something internal to 
> the SoC that the datasheet is lacking on detail about.
> One of the reasons for the regulator-always-on being in the dts was so that 
> the regulator didn't get touched and so didn't break anything.
> All said and done, it only takes a minute with a multimeter to determine 
> actual defaults. Helpful to have multiple boards to gain some confidence 
> that they behave the same, but still basing values like this on tiny 
> sample sizes is probably unwise.
> Looking at other A20 based boards, Cubieboards for example, shows LDO3/4 
> being unused and the VCC-PE/PG pins they power on the lime2 being tied 
> directly to 3.3v. No issues there simply because there's no way to mess 
> with the power to those blocks.
> The patch you really want is something like the one below which works 
> on my boards regardless of the presence of regulator-always-on.
> Verified on four boards with u-boot 2016.03 and kernel 4.5.0.
> Whether you decide to remove regulator-always-on or not is a different 
> question, but please use 2.3v, or some other proven working value, for 
> ldo3. At least that way you have a fighting chance of the board 
> remaining functional when something wants to turn the regulator on.

Hi Iain,

thanks for the feedback.

I have yet to try your patch, but I have broken out the multimeter to
measure LDO3. On GPIO-2, I'm measuring 2.8V between pins 2 and 4 instead
of 2.3V you seem to measuring.
In my setup, I have simply removed the SD card from the lime2 to get
whatever defaults are used at boot.

How did you measure LDO3? Also, did you find any pins for LDO4 besides
the AXP209 itelf? Mine seems to be covered in flux.


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