imx6ull: random crashes when setting REFTOP_SELBIASOFF

[Fabio Estevam]

Hi Heiko,

On Fri, Jan 24, 2020 at 2:33 AM Heiko Schocher <hs at denx.de> wrote:
>
> Hello Fabio, Peng,
>
> I have here an imx6ull based board from DH electronics [1]
> which has the IMX_THERMAL driver enabled in U-Boot and Linux. We
> see on Linux boot random crashes (random means not on every boot,
> also not even the same crash dump/reason in linux). My first
> suggestion was instable RMA, but RAM seems stable.
>
> After some investigation it turned out, that setting the
> REFTOP_SELBIASOFF bit in the linux thermal driver seems the problem.
>
> I saw that the kernel driver does not check first if REFTOP_VBGUP
> is set and added this, but this did not helped.
>
> U-Boot does this check here:
>   https://gitlab.denx.de/u-boot/u-boot/blob/master/arch/arm/mach-imx/mx6/soc.c#L342
>
> More investigation into this problem and we found how U-Boot handles
> this bit:
>
> U-Boot: sets this bit in  arch_cpu_init()
> U-Boot: sets this bit in IMX_THERMAL driver
> U-Boot: clears this bit in IMX_THERMAL driver
>
>
> If we now remove the clearing of this bit in U-Boot in the thermal
> driver, we also see no crashes anymore in Linux (more than 12000
> power on/off cycles)
>
> My question is now,
>
> - do you now more about this bit as in the RM is described?
>    Or know somebody we can ask?
>
> - What effect has this bit? May it leads in more power consumption?
>
> - Is it valid to not clear it in U-Boot?

I was not aware of such problem and not familiar with these details.

I think someone from NXP hardware team would have to take a look and confirm.

Please post these question at the i.MX community forum:
https://community.nxp.com/community/imx

Thanks