[PATCH v2 2/2] ARM: mxs: Pass the system revision

Michael Heimpold mhei at heimpold.de
Sat Jun 1 18:11:16 EDT 2013

Hi Fabio,

Am Samstag, 1. Juni 2013, 11:58:18 schrieb Fabio Estevam:
> Can you please provide some real examples?

Please have a look at e.g. mach-orion5x/dns323-setup.c or grep for
system_rev in arch/arm.
An out-of-vanilla-tree example is a board I've worked on:
In arm/mach-omap2/board-omap3touchbook.c I'm not able to tell whether
the use system_rev to encode a PCB revision or a CPU revision.

> If you look at FSL kernel code the system revision is hardcoded in the
> board file.
> For mx5/mx6 boards we do pass ATAGS from bootloader to kernel in the
> same format it was used here.

I see it. But I still wonder whether this is the right direction to pass the
SoC revision to user-space. And I feel uncomfortable when we're
mixing it with a board revision. I would prefer dedicated lines in /proc/cpuinfo.
Is there a policy about adding line which would prohibit this?

> As I mentioned in the commit log, the only reason we are doing this
> here is to allow a mainline kernel to run som mxs applications like
> Gstreamer plugins and kobs-ng.

I only know the kobs-ng util but I got the point: these tools (only) look at the
revision line and cannot be used with a mainline kernel at the moment
as a vanilla kernel don't pass the information required by these tools.

However, the revision field is arm platform specific and should be used with
the same purpose over all mach types. Interpreting it for different SoCs
in a different manner is IMO not a good idea.

So my question are:
What was/is the real intension for system_rev?
Is passing a PCB revision via ATAG obsoleted by DT?


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