[RFC PATCH 1/1] powerpc/embedded6xx: Add support for Motorola/Emerson MVME5100.

[Stephen N Chivers]

Scott Wood <scottwood at freescale.com> wrote on 08/13/2013 08:04:30 AM:

> From: Scott Wood <scottwood at freescale.com>
> To: Stephen N Chivers <schivers at csc.com.au>
> Cc: Chris Proctor <cproctor at csc.com.au>, Kumar Gala 
> <galak at kernel.crashing.org>, <linuxppc-dev at lists.ozlabs.org>, 
> <paulus at samba.org>
> Date: 08/13/2013 08:04 AM
> Subject: Re: [RFC PATCH 1/1] powerpc/embedded6xx: Add support for 
> Motorola/Emerson MVME5100.
> 
> On Tue, 2013-08-13 at 08:57 +1100, Stephen N Chivers wrote:
> > Scott Wood <scottwood at freescale.com> wrote on 08/09/2013 04:07:24 AM:
> > 
> > > From: Scott Wood <scottwood at freescale.com>
> > > To: Kumar Gala <galak at kernel.crashing.org>
> > > Cc: Stephen N Chivers <schivers at csc.com.au>, <paulus at samba.org>, 
> > > <linuxppc-dev at lists.ozlabs.org>, Chris Proctor <cproctor at csc.com.au>
> > > Date: 08/09/2013 04:08 AM
> > > Subject: Re: [RFC PATCH 1/1] powerpc/embedded6xx: Add support for 
> > > Motorola/Emerson MVME5100.
> > > 
> > > On Thu, 2013-08-08 at 10:30 -0500, Kumar Gala wrote:
> > > > Also, we don't take full defconfigs in the tree, look at 'make 
> > > savedefconfig'
> > > 
> > > Why does this board need its own defconfig at all?  Just add it to
> > > ppc6xx_defconfig.
> > 
> > The boards firmware as stated above is PPCBug. PPCBug is not Open 
Firmware
> > compatible.
> > 
> > There is no U-Boot support for the board.
> 
> I'm not sure why that precludes the use of ppc6xx_defconfig...
> 
> > In ppc6xx_defconfig the e100 network device and NFS support is modular 
and
> > that forces the use of an initrd.
> 
> OK, then let's enable those in ppc6xx_defconfig.  We do in a lot of the
> other defconfigs (such as 85xx and derivatives).
> 
> > PPCBugs network boot command takes only one file argument and so makes
> > it difficult to use an initrd.
> > 
> > So the choices are:
> >         - Providing a defconfig for the board,
> >         - Building the kernel with the initrd embedded in it,
> >         - Finding an alternative boot loader,
> >         - Doing the board support for U-Boot.
> > The first choice is simple and documents the configuration of the
> > board without mixing it into ppc6xx_defconfig.
> 
> The first choice means your board would get much less build-testing, and
> would increase maintenance costs of defconfig changes (and/or lead to
> divergence from other defconfigs that doesn't actually have anything to
> do with this board or its use cases).
> 
> The fifth choice is "add what you need to ppc6xx_defconfig".  Within
> reason of course, but I think a common PCI network device and NFS root
> support is reasonable.
Thanks for the suggestion.

I have tried it and ppc6xx_defconfig does generate a viable kernel for
the MVME5100 but there is a total lack of serial console messages.

The reason is due to the requirement for a register shift to access the
UART register(s) on (via) the HAWK ASIC. The HAWK ASIC is very likely to
be a MPC107/TSI107, making it compatible with "tsi-bridge". The TSI
bridges also require register shifts to access their "built-in" UARTS.

I will check the MPC107 data sheet against the TSI107 datasheet
and the MVME5100 programmers manual later today.

The serial console setup in 'legacy_serial' does not support reg-shift
or reg-offset properties and so a preferred_console is not added by it.
The DTS file for the board does specify the register shift so that
'of_serial' will correctly setup the UARTS. But that is too late, the
preferred console will be tty0 as the .config derived from 
ppc6xx_defconfig
has CONF_VT_CONSOLE set. In the test kernels I have built 'con_init' in
the VT support is always called before serial8250_console_init.

I did try modifying legacy_serial to correctly support the tsi-bridge
UARTS and add the preferred console but encountered even more problems
in 8250_core when registering the serial console (to the point of
having a silently panic'ing kernel).

So I think for the moment, the board will need its own default config.

I think similar problems would occur for the Holly and MPC7448_HPC2 boards
as these also have tsi-bridges, but their dts files do not specify the
reg-shift properties. This begs the question do the serial consoles
for Holly and MPC7448_HPC2 actually work?
> 
> -Scott
> 
> 
>