[PATCH] cmd: boot: Update reset usage message

[Wolfgang Denk]

Dear Michal,

In message <90e6c670-9e11-beb8-bcb5-9d22ba00fd11 at xilinx.com> you wrote:
> 
> > In case of the hard (cold) reset - is it really only a reset of the
> > CPU, or of the whole board hardware?
>
> If you look at sysreset headers you will find these levels
>  11         SYSRESET_WARM,  /* Reset CPU, keep GPIOs active */
>  12         SYSRESET_COLD,  /* Reset CPU and GPIOs */
>  13         SYSRESET_POWER, /* Reset PMIC (remove and restore power) */
>  14         SYSRESET_POWER_OFF,     /* Turn off power */
>
> When you call reset sysreset uclass is calling sysreset_walk which is
> request to drivers with type passed.
> I see we have mixed drivers which deals with levels and especially in
> gpio case it is question how you connect it.
> I develop this for microblaze where gpio is connected reset logic which
> is normally only for CPU and subsystem.
> But in general you can connect whatever you want. It means it doesn't
> need to be only cpu which is reset.

Thanks a lot for the explanation.

> Do you want me to update that line and remove CPU from it?

I don't know :-)

What the "reset" command _should_ do is a hard cold boot including
the reset of all peripherals - for example, when booting from SPI
NOR flash it is mandatory to reset this flash to make sure the ROM
boot loader can actually read it.

I would appreciate if the help message documents what it actually
does.  Also, what the difference between "cold" and "warm" reset is.
My expectation (without knowing any hardware details) would be that
a warm reset is just a restart of the already loaded code? Or is it
just a reset of the CPU (without external reset)? This might then
hang the system if it's attempting to boot from a flash which is in
the wrong state.

So my problem with this is primarily that I don't understand what
the command really does, and the help command is of no help either.

[And if I understand correctly, this is even board dependent?]

Best regards,

Wolfgang Denk

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