[U-Boot-Users] [PATCH] Blackfin: implement go/boote wrappers

[Mike Frysinger <vapier@gentoo.org>]

On Monday 21 April 2008, Wolfgang Denk wrote:
> In message <200804211658.44036.vapier@gentoo.org> you wrote:
> > > I tried understanding what you are trying to do, and  even  though  I
> > > feel  it's  not  exactly  an important or frequently used feature for
> > > most of the users I tried to come up with a  compromize  that  allows
> > > you  to  do  what  you  want to do without hurting others and without
> > > polluting the command name space.
> >
> > i consider the cache one aspect of it.  the users shouldnt have to know
> > "oh i gotta turn off cache", they just have to know "i'm loading up my
> > code and
>
> I agree that  cache  is  just  one  aspect;  I  disagree  that  users
> shouldn't  know what they are doing. On contrary, I want to give them
> all necessary control to do what they may want to do. It is a  matter
> of higher software levels to provide more convenient abstractions.

yes, but the fact that we have to turn off caches is not for performance 
reasons.  users should not need to be aware of these system deficiencies 
which is why i'm proposing a "noret" flag.

> > it's going to take over the system".  that is why a "-noret" flags makes
>
> Who says that *my* application which doesn;t return does the same  as
> your  application?  Maybe  I *want* to have the caches on for perfor-
> mance?

i'm not concerned with the performance aspect.  caches on the Blackfin are 
intertwined with protection, and protection handlers require a software 
vector to process exceptions.  the act of executing a program that takes over 
the system means the exception handler is no longer reliable so i have to 
guarantee it wont be called.  based on information given to me from our 
hardware team, this can only be accomplished implicitly by disabling caches.

> I accept that the default settings may be not optimal  for  your  use
> case,  so please accept that your settings may not be always optimal,
> either. As a solution I imagine options to the "go" command.  If  you
> consider  this  too  complicated  for your users, please feel free to
> provide an alias in an envrionment  variable  which  your  users  can
> "run".

i completely accept that the patch i posted to turn off caches for all things 
to "go" result in a suboptimal environment for standalone u-boot 
applications.  for Blackfin usage though, that takes a back seat to things 
silently crashing.

> > applications (while useful) dont really matter.  such applications rely
> > on u-boot remaining resident which is the opposite of what i'm talking
> > about.
>
> But then it doesn't hurt, does it? Your application can do anything it
> wants as long as it does not attempt to return to U-Boot.

except that it may inadvertently do so on Blackfin.
-mike
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