[U-Boot] [PATCH 07/14] dm: dts: omap: Select correct console for beaglebone

[Tom Rini]

On Wed, Oct 22, 2014 at 09:19:08PM -0600, Simon Glass wrote:
> Hi Tom,
> 
> On 22 October 2014 09:59, Tom Rini <trini at ti.com> wrote:
> > On Mon, Sep 22, 2014 at 09:48:47AM -0600, Simon Glass wrote:
> >
> >> Select serial0 as the console.
> >>
> >> Signed-off-by: Simon Glass <sjg at chromium.org>
> >> ---
> >>
> >>  arch/arm/dts/am335x-bone-common.dtsi | 4 ++++
> >>  1 file changed, 4 insertions(+)
> >>
> >> diff --git a/arch/arm/dts/am335x-bone-common.dtsi b/arch/arm/dts/am335x-bone-common.dtsi
> >> index 2f66ded..e70b4d1 100644
> >> --- a/arch/arm/dts/am335x-bone-common.dtsi
> >> +++ b/arch/arm/dts/am335x-bone-common.dtsi
> >> @@ -10,6 +10,10 @@
> >>       model = "TI AM335x BeagleBone";
> >>       compatible = "ti,am335x-bone", "ti,am33xx";
> >>
> >> +     chosen {
> >> +             stdout-path = &uart0;
> >> +     };
> >> +
> >>       cpus {
> >>               cpu at 0 {
> >>                       cpu0-supply = <&dcdc2_reg>;
> >
> > So here's where I worry.  The reason we have a Kconfig for CONS_INDEX is
> > that there are boards it's NOT uart0.  Setting aside the people with a
> > "uart cape" (or otherwise breadboarding out another uart to a real
> > connector), the industrial EVM is uart2 I want to say and we had been
> > happily supporting this board with just a different build target (then
> > defconfig).  What can we do here?  And yes, I see this is the bone DT
> > not the EVM dt, but I'd rather not have to, if we don't have to at
> > least, default to just not supporting the board (which is at least on
> > the table, there's no DT for it in the kernel either).
> 
> I think we are looking for a build-time way to change the console. Is
> that right? I suppose we could use a #define in the device tree, set
> from some sort of include file / option, but that seems pretty ugly.

It does, yeah.

> It would not be hard to modify the DT in the binary after it is built,
> if that helps.
> 
> We can certainly support a different build target with a different
> 'default' device tree. We would then have several .dts files all
> including the .dtsi for their main body.
> 
> Also there is a patch that I have not tidied/sent yet which builds all
> the .dtb files for a class of boards, so you can add the .dtb that you
> prefer to U-Boot with 'cat'.

We'll need that at some point, sooner rather than later since
"am335x_evm" works on 4 distinct platforms, not counting the one where
console is on a different UART than expected.

> I'm open to various options here, but I'm not sure which is best for
> this use case.
> 
> I wonder how the kernel deals with this issue?

I think the answer for how the kernel deals with it is "out of tree".
Maybe that's the good enough for now answer here too.  It's just a
matter of providing the correct device tree for the EVM in question, so
maybe we just punt.

-- 
Tom
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