[PATCH] socfpga: Find partition with environment via device tree

[Trent Piepho]

On Mon, 2015-12-14 at 11:01 +0100, Sascha Hauer wrote:
> On Fri, Dec 11, 2015 at 08:05:00PM +0000, Trent Piepho wrote:
> > On Fri, 2015-12-11 at 10:30 +0100, Sascha Hauer wrote:
> > > On Fri, Dec 11, 2015 at 02:13:21AM +0000, Trent Piepho wrote:
> > > The "barebox,environment" compatible describes a binding which takes
> > > partition described in device-path as a raw file containing a barebox
> > > envfs.
> > 
> > Well, I redefined it to have the device-path be the device containing
> > the environment as raw data or the one containing a filesystem with the
> > environment as a file if the architecture expects that.
> > 
> > That doesn't seem like a bad definition.
> 
> No, indeed not. It's more the implementation I have a problem with. The
> implementation should be done in the environment driver.

Ok, my second attempt moved it to the barebox env OF driver.  This seems
better as it unifies the boards that have an env on a device and those
that put it in a file.

> > > What you have here is a partition which contains a FAT which has a
> > > barebox envfs in a file. I think it's fine to extend the binding (and
> > > the barebox env driver) to handle that case.  What you are doing here is
> > > to smuggle code behind the driver and bend the environment path to
> > > somewhere else. That is not ok. I think what we can do is to add some
> > > file-path property which contains the path and tells the barebox
> > > environment driver to not use the whole partition but instead to mount
> > > it and use the file specified in the file-path property.
> > > 
> > > As an alternative which I might even like better is to extend the
> > > partition binding to be able to describe a file in a partition, like:
> > 
> > This won't work.  mmc devices, which all boards that use a file for the
> > env are using, don't have partitions in the device tree, since they are
> > created dynamically from the partition table.  There is nowhere to put
> > the file node.
> 
> Just because they are dynamically created from information found on the
> MMC card doesn't mean we can't describe them in the device tree. We can
> for example specify "The second partition" or "The partition with UUID
> xy".

That would be hard to do in practice, as the UUID of a partition is
normally generated at random when the partition is made.  It would be
hard to keep the UUID in the device table matching the partition table.
I suppose one could go by partition number or by name too.  Which is
really no different than the partname: syntax but in a different
location.

> > It is also problematic for my board.  I need to change the env path
> > based on data in an eeprom that selects which partition to use.  Other
> > boards that have multiple environments select them in a
> > postcore_initcall using boot strapping pins that aren't part of a
> > device.  I'm using an eeprom so I need to do the selection later in the
> > init process.
> 
> Ok, so you couldn't you do the same?

Yes, I made it work with my second attempt.  The env driver is a
late_initcall so I was able to have board code modify the OF tree so
that it points to the correct partition.

> > Maybe extend load_environment to do the mount?  const char
> > *default_environment_path would have to change to something that could
> > support the concept of a device + optional filename.  This way one could
> > change the env path upto environment_initcall() time.
> 
> My original plan was to extend this:
> 
> 	device-path = &mmc, "partname:1";
> 
> with a filename, like this:
> 
> 	device-path = &mmc, "partname:1", "/bla/env";
> 
> I found out that this is not how the device tree should be like. It
> looks and feels better when the phandle directly points to a node and
> the node describes a partition (or file in this case).

I thought the env code was intentionally not using phandles so that it
could be in a different DT than the DT describing the hardware.  Thus
the path instead of a phandle.

I didn't want to extend device-path with an optional 3rd string since
device-path is already IMHO too complex supporting both a path to a
partition or a path to a device and then a partition description.  So
one would also want to support device-path = &eeprom, "/bla/env" and now
you've got to guess if the 2nd string is a file or partition name.

So I've guess we have:

{
  compatible = "barebox,environment";
  device-path = &foo, "partname:bar";
  file-path = "baz";
}

OR

{
  compatible = "barebox,environment";
  env-path = &environment;
}

&foo {
  partition at 0 {
    label = "bar";
    environment: file at 0 {
      path = "baz";
    };
  };
}

So the same information but in a different layout.  The latter layout is
more complex and I'm not sure how the code would properly tell if the
node path refers to a device or a partition or a file.