ARM Machine SoC I/O setup and PAD initialization code

[David Jander]

On Thursday 22 July 2010 05:00:56 pm Nicolas Pitre wrote:
> On Thu, 22 Jul 2010, David Jander wrote:
> > On Thursday 22 July 2010 02:56:52 pm Mark Brown wrote:
> > > On Thu, Jul 22, 2010 at 02:10:09PM +0200, David Jander wrote:
> > > > IMO, if a bootloader is broken (in any way), it needs replacing. Be
> > > > it with another bootloader or directly with the kernel.
> > >
> > > If you don't have JTAG access (either due to device limitations or due
> > > to lack of data from the vendor of a reference platform you're using)
> > > replacing a bootloader can be rather more stressful than it's worth.
> >
> > I agree, but I simply can't believe ARM platform designers all do such a
> > bad job at firmware (=bootloader) development in general, which is in
> > sharp contrast to what I have learned from previous PowerPC developments.
> 
> Well, this obviously didn't impair the success of the ARM architecture,
> nor did crappy BIOS has impaired the x86 architecture.  Becoming
> "mainstream" as the ARM architecture is becoming is always bound to
> create crap on the edges, such as poorly revised bootloader code.  And
> just as on X86, it is often better to simply not rely too much on the
> bootloader.  Mistakes and bugs will always happen in both the kernel and
> the bootloader.  But it is much more easier and efficient resource wise
> to fix a config bug in the kernel and updating it on the affected kernel
> than it is for fixing the same bug in the bootloader and updating the
> bootloader there.

Not quite. On x86, you have the BIOS, and you really do need to rely on the 
BIOS to setup such low-level stuff correctly, and no, you cannot fix that in 
the kernel!
Even more so: The linux kernel is exactly the same binary for every PC it runs 
on. That's possible, because in the PC world (as crappy as it is otherwise) 
there actually _is_ a standard.

> > Even if it works with one guessed setting, there is a potential EMC
> > impact that needs to be taken care of.
> 
> What I've implemented so far is the ability to either set some
> parameters, or keep the existing ones, but not require for the kernel to
> have to setup everything up.  So if you don't know the right value for a
> setting as a kernel developer then you may just elect to leave it alone
> and hope that the bootloader has set it right.

Well, that's essentially the whole problem I see. Why not try to create a 
standard for such stuff on ARM. Maybe we would need the power of a few big 
players to get it in, maybe Linaro, or some other. IMHO it's about time there 
is more standardization on the ARM platforms that manufacturers do apply in 
their designs.

> > There are important hardware-design decisions after each of those
> > settings! If we continue this amateuristic approach, ARM-linux platforms
> > will never get taken seriously in more demanding environments. This
> > really needs to change.
> 
> You are more than welcome to change this state of affairs.  And if you
> truly succeed where we all failed so far then it will only be a matter
> of removing the made redundant and useless setup code in the kernel.

Please, my intention is not to be arrogant. I just want to make sure there is 
a need for something like OF from PowerPC or a similar standard. Introducing 
the change is another problem... let's just try to agree on something in the 
first place.

Of course, I will do what I can to help move in the right direction, and once 
there is a good standard, you have my word that I'll make sure all my hardware 
designs will adhere to it.

Best regards,

-- 
David Jander
Protonic Holland.