[meta-freescale] minimal DT changes to start booting kernel on D/L board on ttymxc3?

[Otavio Salvador]

Hello Robert,

On Wed, Oct 11, 2017 at 7:57 AM, Robert P. J. Day <rpjday at crashcourse.ca> wrote:
>
>   this *should* be a simple question but i just want to make sure i'm
> not overlooking anything, costing myself hours of aggravation.
>
>   for a freescale MCIMX6Q-SDB reference board in front of me, i've
> trivially built a "core-image-minimal" using MACHINE=imx6qdlsabresd,
> dd'ed the wic image to SD card, and booted perfectly successfully. so
> i now have a kernel that should cover a wide range of i.MX6 targets,
> differing only in the .dtb file passed to the kernel at boot time.
>
>   the only detail of interest is that this board clearly has its
> console on UART1, as /proc/cmdline contains:
>
>   # cat /proc/cmdline
>   console=ttymxc0,115200 root=PARTUUID=0b867308-02 rootwait rw
>   #
>
> where, as i read it, for i.MX6, the association is:
>
>   UART1 -> ttymxc0
>   UART2 -> ttymxc1
>   UART3 -> ttymxc2
>   UART4 -> ttymxc3
>
> correct? and herein lies the issue.
>
>   i have recently been handed a proprietary i.MX6-based board, built
> around dual-lite but, as i've been told, trying to hang onto as much
> of the MCIMX6Q-SDB design as possible to minimize the churn in the
> device tree files. still, there's a ton of stuff that's been added to
> the proprietary board, so certainly the DT files are going to be
> different and will need major tweaking.
>
>   what i want to do is start with a generic YP build as above, and
> just boot using (i'm assuming) "imx6dl-sabresd.dtb" that was built as
> above; in other words, i already have everything i need from the
> current build, i just need to stop in u-boot and switch the .dtb file
> being passed to the kernel.
>
>   i'm prepared for all sorts of warnings and errors given that the DTB
> file won't match the actual board, but the fundamental issue is that
> the console port on this proprietary board was (apparently) moved from
> UART1 to UART4, since (for this proprietary board and a working but
> fairly old bootable image) u-boot sets "console=ttymxc3,115200". so my
> plan is to simply define a new layer (meta-rday or whatever), which
> defines a new MACHINE, and tweaks the meta-freescale kernel with a
> single patch that defines UART4 as the console rather than UART1.
>
>   does that make sense? as i said, the rest of the DT files will
> certainly be out of whack and i'll start adjusting them as errors come
> up and i add support for new subsystems, but just to start getting
> kernel output, is it sufficient to just move the DT console definition
> from UART1 to UART4? is there anything else that would need to change?
>
>   oh, and while i'm about to dig into the device trees to see how to
> do that, if anyone wants to just supply the kernel patch i would need
> to apply, that would be just ducky. :-)
>
>   does all this make sense?

Not much ;-)

Generally we do this kind of development using:

- a toolchain and building the U-Boot and Linux kernel outside the OE
build system as it is way faster, easier and more productive
- when those are good, we integrate them in a customer layer
- make a custom machine for the customer on this layer
- enjoy ;-)

This way you have more control and is not affected by changes on the
other layers. It is safer and also keeps clear what are the specific
components of your board.

-- 
Otavio Salvador                             O.S. Systems
http://www.ossystems.com.br        http://code.ossystems.com.br
Mobile: +55 (53) 9981-7854            Mobile: +1 (347) 903-9750