Re: [PATCH 4/9] omap_uart: add low level port serial initialization

[Sascha Hauer <s.hauer@pengutronix.de>]

On Sun, Mar 10, 2013 at 11:44:31PM +0100, vj wrote:
> >
> > You can't access global variables at that state. They are
> > addressed with their absolute address which will not be correct
> > when you are not running at the linked address. You can simply
> > verify that by doing a PUTHEX_LL("somestring"); You will see
> > the address the string is located when running from the correct
> > address.
> >
> > Sascha
> >
> > --
> > Pengutronix e.K.                           |                             |
> > Industrial Linux Solutions                 | http://www.pengutronix.de/  |
> > Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0    |
> > Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |
> 
> So the problem is not with PUTS_LL, it's with who calls it that should
> modify the string pointer accordingly.
> And what are the limitations of not having stack? local variables,
> calling non-inline functions, more?

Local variables work fine.
Without stack you can only use __naked functions. With these the
compiler does not save the registers to the stack and you can't return
from them. This means a function should always end with a call to
another function. Normally you should only setup a stack here and call
a function which then can use it.

Another limitation is that you can only pass three arguments to a
function, more arguments would be pushed on the stack.

Also functions must not become too complex, because otherwise the
compiler would make use of the stack inside the function.

The typical register write stuff you normally do in such lowlevel
init work fine.

Sascha

-- 
Pengutronix e.K.                           |                             |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |

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