[PATCH v2] ARM: remove name from machine_desc for DT platforms

[Olof Johansson]

On Tue, Nov 05, 2013 at 08:34:56AM -0600, Rob Herring wrote:
> On Mon, Nov 4, 2013 at 5:36 AM, Grant Likely <grant.likely at secretlab.ca> wrote:
> > On Sun, Nov 3, 2013 at 8:50 PM, Rob Herring <robherring2 at gmail.com> wrote:
> >> From: Rob Herring <rob.herring at calxeda.com>
> >>
> >> As part of the effort to ultimately remove struct machine_desc, the
> >> machine name is not really needed. It is only used for /proc/cpuinfo
> >> "Hardware" field. Get this information from the DT instead and remove
> >> the name string in the machine descriptor for DT machine descriptors. The
> >> model or machine compatible property from the DT is used instead.
> >
> > I've obviously missed some discussions because I wasn't aware of the
> > plan to remove machine_desc. That's neither here not there, but for as
> > long as the structure still exists it is really useful to discover
> > which machine_desc the kernel chooses at boot time. If you're going to
> > remove this, then at the very least I would embed the filename or
> > something similar into the machine desc so it is available for
> > debugging. It can go away when the structure is removed.
> 
> It's a very long term goal to remove it completely, but it is now
> optional for "simple" platforms with the default machine_desc and
> default init ptrs. You might want to look at the patches and the WIP
> branch I posted[1] which removes the machine_desc for highbank.
> There's some core boilerplate I'd like your opinion on. Also, I'm sure
> you are aware of the resistance to add a machine_desc to arm64, so I'm
> looking at this from that perspective as well. I'm sure there will be
> platforms which look very similar across arm and arm64.
> 
> On boot, the model or compatible string from the DTB is printed out
> (that change is actually in my DT arch clean-up series, not this
> patch). This has made what is printed out on boot consistent across
> arches using DT. There is no good reason for this to be arch specific.
> Presumably the compatible string is unique and just as easily grepped
> for in the kernel source as the machine_desc name is. Adding a
> filename string here seems like useless bloat to me.

I think I agree a bit with Grant's concern here.

The compatible string is unique, but the machine descriptors might not
be -- a given device tree might match two of them (one more generic,
one more specific) -- it would be useful to know which one was used. Or,
if you missed to enable the platform support for your board so it booted
with the generic descriptor, but you still needed your own.

Matching it back to which devicetree the kernel was booted with shouldn't be
hard, I agree -- but knowing which machine entry was picked at boot time
is still useful information.

-Olof