[U-Boot] [PATCH] imx: don't clobber reset cause

[Eric Nelson <eric.nelson@boundarydevices.com>]

Hi Stefano,

On 02/05/2015 10:52 AM, Stefano Babic wrote:
> Hi Eric,
> 
> On 05/02/2015 18:22, Eric Nelson wrote:
> 
>>>> There is very similar code in 'arch/arm/cpu/armv7/vf610/generic.c'.  The
>>>> write is for a hard power on case where these reason registers are full
>>>> of weird bogus values (at least on Vybrid; I suspect on iMx).  In the
>>>> case of a non-POR, the register bits are good.  However, if you don't
>>>> clear the status, on the next reset it may have multiple registers bits
>>>> even though you really want to know the last reason (bit).
>>>>
>>>> Another option would be to clear the value and store the 'cause'
>>>> somewhere for other U-Boot users.  Unless you wanted to read this from
>>>> an OS?  I think both files should behave the same, all else equal.
>>>>
>>>
>>> I have assumed (maybe wrong ?) that the reason for the patch is to let
>>> the OS reading these bits.
>>>
>>
>> In some cases (Windows Embedded), yes.
>>
>> In the Linux case, we'll likely pass the value to the kernel through
>> the kernel command-line, so it's available to userspace.
>>
>> I'm not aware of any kernel functionality for this at the moment.
>>
> 
> It remains the issue raised by Bill (thanks for that). If the bits are
> not reset, we can determine the cause only after POR, but not anymore
> after a warm start. Can you maybe use the IRAM to pass the information
> to Windows ?
> 

Certainly, but it seems wrong to make a decision about where and how
this might get passed to an O/S in code.

If we want to generalize it, I'd be inclined to add commands to
query (into a variable) and clear the reset cause.

That would still require this patch though.

Regards,


Eric