[U-Boot] [PATCH] M28: Added guarding for reserved bits in GPIO driver

[Marek Vasut <marek.vasut@gmail.com>]

> > To make things simple for users, there's standard layout. It's actually
> > at sector 2048 btw.
> 
> Got that.
> 
> > That's what happens internally, it's just that some pieces (like sector
> > offset of the partition!) need to be filled into the bootstream header
> > by the mxsboot utility -- see mxsboot -h for how to change that.
> 
> You're completely right! This sector needs to be know build-time because it
> is specified in the Boot Stream Block of the Boot Stream header. I forgot
> about that, because I hid that in a script some time ago. That script was
> basically a rewritten version of the broken one that was supplied with the
> SDK.
> 
> Come to think of it, it's a bit weird that the sector the BSB is located
> in, is specified in the BSB: When reading it, it already knows this
> sector, because that's the sector it is reading from at that moment...
> 
> > The 2048 sector offset was chosen because that's standard in Linux now
> > for first partiiton.
> 
> Agreed.
> 
> > What do you mean?
> 
> What I meant to ask was how you solved the paradoxic problem that U-Boot
> needs to initialize SD-RAM before it can be loaded (and obviously U-Boot
> needs to be loaded before it can initialize SD-RAM).

Well we have U-Boot SPL, which is loaded into SRAM, inits DRAM, pinmux etc., 
then we pass execution back to BootROM to load U-Boot into DRAM and execute it.

> 
> Freescale solved this problem by putting multiple bootlets in their
> bootstream. The first one is small enough to fit SRAM and it enables the
> PMIC's LDOs to power up all power domains. The second one too is small
> enough to fit SRAM. Loading it overwrites the first one and running it
> initializes SD-RAM. The third one is either U-Boot or a Kernel and is
> directly loaded into the now initialized SD-RAM.

Yea, you can load kernel directly via U-Boot SPL too.
> 
> I figured that your solution links U-Boot in a clever way that the lower
> part fitting SRAM will initialize the PMIC and SD-RAM, after which U-Boot
> will load the remainder of itself from MMC into SD-RAM.

See above.
> 
> > You can adjust that, see above.
> 
> Understood.
> 
> Cheers,
> 
>         Robert.