[U-Boot] [PATCH 06/11] tegra20: switch over seaboard and ventana to use tablebased pinmux

[Lucas Stach <dev@lynxeye.de>]

Am Freitag, den 25.01.2013, 06:54 +1300 schrieb Simon Glass:
> Hi Lucas,
> 
> On Fri, Jan 25, 2013 at 5:48 AM, Lucas Stach <dev@lynxeye.de> wrote:
> > Init pinmux in one shot, in order to avoid any conflicts.
> >
> > Signed-off-by: Lucas Stach <dev@lynxeye.de>
> > ---
> >  board/nvidia/seaboard/seaboard.c | 133 +++++++++++++++++++++++++++++++++------
> >  include/configs/seaboard.h       |   3 +
> >  include/configs/ventana.h        |   3 +
> >  3 files changed, 121 insertions(+), 18 deletions(-)
> 
> This seems like a lot of code and presumably quite a bit of
> duplication between boards. What sort of conflicts does this avoid,
> and is it the only way of avoiding them?
> 
I don't see it as duplication, but as explicitly spelling out how the
pinmux configuration should be set up on a certain board.

Before this change we would leave some pads uninitialised in their
(random) reset configuration. For example on the Colibri this leads to
NAND not working as it's wired up to the KBC pads. If we only configure
those, ATC will remain in it's reset state and would be also configured
to the NAND function, which leads to fail. Having an explicit, known to
be conflict free configuration for all pads avoids all those unpleasant
surprises.

> Also, how does this deal with drivers that want to support different
> configurations, such as 4/8 bit MMC, UART flow control, etc.? How does
> this fit with what the device tree pinmux specifies in the kernel, and
> why would we not move to using that?

This is just the pinmux. You have to make sure to match the pinmux with
your driver configuration. This tablebased approach is the same thing as
what is done with Tegra30 in U-Boot.

It's not as runtime flexible as the pinmux used in the Linux kernel, but
also quite a fair bit simpler. I don't see any platform that would need
anything other than the default configuration in U-Boot, so we don't
need the muxing stuff provided by the pinmux framework in the kernel.

While running U-Boot we want to keep most of the pads in tristate and
just enable the ones used by U-Boot itself (boot devices, GPIOs, LCD
pins, etc.), so using the plain kernel pinmux config isn't going to
work. So I think the table based approach is a good compromise between
the need of having an comprehensively defined pinmux, simplicity and
effort needed to define the pinmux.

Regards,
Lucas