Re: BeagleBone support, omap1, omap2, omap3, etc.

[Niek Linnenbank <nieklinnenbank@gmail.com>]

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Hello Philippe and Esteban,

On Tue, Dec 10, 2019 at 10:55 AM Philippe Mathieu-Daudé <philmd@redhat.com>
wrote:

> Hi Esteban,
>
> On 12/3/19 4:24 PM, Esteban Bosse wrote:
> > Ping
> >
> > El mié., 6 nov. 2019 16:04, Esteban Bosse <estebanbosse@gmail.com
> > <mailto:estebanbosse@gmail.com>> escribió:
> >
> >     Hello!
> >
> >     Some months ago I started to work trying to port the Beaglebone
> >     support from the old qemu-linaro fork to the new QEMU mainstream.
> >
> >     During my work I found that the Beaglebone have an OMAP3 mpu this
> >     mpu has very strong relation with the OMAP2 and OMAP1 in qemu, they
> >     implement a lot of functions in common.
> >
> >     Then I understood that the omap1 and omap2 don't implement things
> >     like QOM and needs a lot of work to upgrade it, at the same time
> >     they are some boards like: omap1_sx, palm, nseries that implement
> >     this mpus.
> >
> >     Looking the datasheet of the omap1 I realized that it's an very old
> >     device and some questions like "make sense work with this old
> >     device?" comes to my mind.
>
> The OMAP3 reuse various components of the OMAP1/2.
> Although in old shape, the OMAP1/2 are in the codebase and work.
> It make sense to me to start upgrading the OMAP1/2 to new QOM standard,
> then add the OMAP3 missing parts.
>
> The previous recommendations from Peter are still valid:
> https://www.mail-archive.com/qemu-devel@nongnu.org/msg636936.html
>
> Or you can use the schema followed by Niek when adding the Allwinner H3:
> https://www.mail-archive.com/qemu-devel@nongnu.org/msg662591.html
>
> That is:
>
> - Add tests using old code (booting Linux, network access in guest)
> - Add an empty board
> - Plug an empty OMAP SoC into the board, add the PoP LPDRAM
> - Add a ARM926 core into the SoC
> - Add most of the devices as UnimplementedDevice
> - Add the interrupt controller in the SoC
> - Add the UART in the SoC
> - Add the Timers in the SoC
> - Try to boot a Linux kernel (UART, TMR, then IRQ tested)
> - Add the SD controller in the SoC
> - Plug a drive to the SD in the board
> - Try to boot u-boot
> - You can now start the OMAP2 using a ARM1136 core
> - Add the missing UNIMP devices (loop to previous steps)
> - Add network controller
> - Run tests (booting Linux, network access in guest)
> - Remove old code
>
> >     When I went to the KVM Forum the last week I talked with some of
> >     you, and you help my with different ideas and proposal to make this
> >     task, but I can't see the right way to make this work because it is
> >     a lot of work.
> >
> >     My motivation is learn more about embedded devices, architecture,
> >     kernel, etc. and of course contribute to the community.
> >
> >     I would love to hear your opinions about this 3 related devices with
> >     they respected boards.
> >
> >     Maybe someone is interested to work with me.
> >     I dream to make this work beautiful (like the musca board with the
> >     armsse and armv7m modules) with a good variety of tests. And in the
> >     same time I would like to write some documentation about the process
> >     with the final idea to "make an easier way for new contributors".
>
> Very good idea.
>
> Niek, since you recently did the same, do you mind sharing your
> experience, tell us what was not clear or hard to understand, so we can
> have a better idea what part of the documentation/process we should
> improve first, to help and welcome new contributors?
>

Sure! Based on my own experience with the Allwinner H3, I can fully
recommend the steps
described above by Philippe to get the work done. Those are mostly the
things I did as well.

I think the best advice I can give you to get started is, start with the
bare minimum: kernel output.
What I mean by that is, get the linux source and compile it for your target
machine. Next, take the QEMU source and choose
any existing machine that come closest to the machine or SoC that you want
to implement.
Then, just try to get the kernel output working via the serial console by
loading it with -kernel, -append and -dtb arguments.

If you are lucky, serial output already works since the machine is similar
to the one you want to implement. If not,
you may need to check for things like the load address and DRAM addresses
first and try to get output
by reading the kernel dmesg via GDB [1]. If you start QEMU with -s -S
arguments, connect with gdb
and give the 'lx-dmesg' command you'll read the kernel output before it
goes to the serial device.
If you at least selected the right processor and things like the load
address are OK, chances are good
that you at least get some logging.  And then, you have a starting point to
start the real work using the
steps described above by Philippe.

Regards,
Niek

[1]
https://www.kernel.org/doc/html/v4.10/dev-tools/gdb-kernel-debugging.html



>
> >
> >     If someone want to work with me in this task, should know that I
> >     don't have to much experience and I'm doing this job in my free time
> >     (this means that I work only in my free time).
> >
> >     I appreciate any kind of comment or advice.
> >
> >     Thanks for your time ;)
> >     EstebanB
> >
>
>

-- 
Niek Linnenbank

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