[U-Boot] [PATCH 2/2] fdt_support: Don't panic if unable to perform stdout fixup

[Scott Wood <scottwood@freescale.com>]

On Tue, 2015-09-01 at 20:48 -0600, Simon Glass wrote:
> Hi Scott,
> 
> On 31 August 2015 at 21:16, Scott Wood <scottwood@freescale.com> wrote:
> > On Mon, 2015-08-31 at 21:13 -0600, Simon Glass wrote:
> > > Hi Scott,
> > > 
> > > On 31 August 2015 at 20:11, Scott Wood <scottwood@freescale.com> wrote:
> > > > Currently, using fdt_fixup_stdout() on a device tree that is missing
> > > > the relevant alias results in this:
> > > > 
> > > > WARNING: could not set linux,stdout-path FDT_ERR_NOTFOUND.
> > > > ERROR: /chosen node create failed
> > > >  - must RESET the board to recover.
> > > > 
> > > > FDT creation failed! hanging...### ERROR ### Please RESET the board 
> > > > ###
> > > > 
> > > > There is no reason for this to be a fatal error rather than a warning,
> > > > and removing this allows for a smooth transition on a platform where
> > > > the device tree currently lacks the correct aliases but will have them
> > > > in the future.
> > > 
> > > Why do we need this patch - what platform?
> > 
> > LS2085A
> > 
> > > 
> > > > 
> > > > Signed-off-by: Scott Wood <scottwood@freescale.com>
> > > > Cc: Kumar Gala <galak@kernel.crashing.org>
> > > > Cc: Simon Glass <sjg@chromium.org>
> > > > ---
> > > > Resent with correct address for Simon Glass.
> > > > 
> > > >  common/fdt_support.c | 3 ++-
> > > >  1 file changed, 2 insertions(+), 1 deletion(-)
> > > > 
> > > > diff --git a/common/fdt_support.c b/common/fdt_support.c
> > > > index f86365e..6052c77 100644
> > > > --- a/common/fdt_support.c
> > > > +++ b/common/fdt_support.c
> > > > @@ -308,7 +308,8 @@ int fdt_chosen(void *fdt)
> > > >                 }
> > > >         }
> > > > 
> > > > -       return fdt_fixup_stdout(fdt, nodeoffset);
> > > > +       fdt_fixup_stdout(fdt, nodeoffset);
> > > 
> > > Will some platforms will not boot correctly with this failing? Should
> > > we make your new feature a Kconfig options perhaps? I worry that it
> > > will become the default behaviour and then it will be hard to remove
> > > later.
> > 
> > A warning will still be printed.  I'm not sure how "### ERROR ### Please
> > RESET the board ###" is more useful than trying to continue and possibly
> > failing.
> 
> Only that if it indicates a fatal error the board code can at least
> find out about it and deal with it. Perhaps booting will just result
> in a hang?

If booting results in a hang, then you're no worse off than the current 

situation.  Either way, the user sees a message that indicates the problem.

> I think ignoring errors is fine but here we make it impossible to
> detect a failure. So I think that a Kconfig is the best idea, so we
> can remove it later.

It seems excessive...  Config options aren't free, from a maintenance 

perspective, and I have a hard time imagining a scenario where proceeding to 

boot causes a real problem.

Also, from a consistency perspective:
 - The OF_STDOUT_PATH version doesn't cause a panic if the destination path 
doesn't exist.
 - None of the callers of fdt_status_<foo>_by_alias() panic if the alias is 
not found.
 - do_fixup_by_path() doesn't panic if the node is not found.
 - Neither does do_fixup_by_compatible().
 - Neither does fdt_fixup_ethernet().

-Scott