[U-Boot-Users] dynamic setting of CONFIG_SYS_CLK_FREQ

Wolfgang Denk wd at denx.de
Mon Apr 26 11:14:53 CEST 2004

In message <408CC565.9040006 at intracom.gr> you wrote:
> I'm talking about how the loaded image/kernel gets access to the
> information.
> At that point the variables are placed in RAM, and can contain
> every info that is present in the gd structure.

No. The interface to the (Linux) kernel is (at the  moment,  and  for
PowerPC)  the  bd_info  structure.  Plus  the  params  passed  in the
registers like address and size of the ramdisk and the command line.

> U-boot can continue to use the gd structure, but the application
> can access all it's configuration from the environment variables.
> For example we can fill a environment variable with the system
> clock value at the later stages of initialization.

I do not like this idea. Think about the consequences. It  will  grow
the  environment,  and  "saveenv"  would  write all data to persisten
storage. There are some boards where environment  storage  is  really
tight (like a 512 byte EEPROM). This would cause problems.

Also, it is conecptually not clean. Environment variables  are  meant
as  user  (or  at  least manufacturer) configurable data which can be
edited and changed. They are NOT intended  for  other  purposes  like
storing data that is available otherwise. I know that this concept is
not  kept  very  strictly  -  for  example, the "version" environment
variable is IMHO bogus because the U-Boot version  can  be  displayed
with  the  "version" command - but then there was the (valid) request
from users to check the U-Boot version from the running Linux system,
so I gave in.

But please let's keep the environment as clean as possible.

What you are trying to  do  really  asks  for  an  implementation  of
bi_recs; if we had such a list of feature records you could easily do
what  you want to do. And we could even use this directly to pass all
this information to Linux.

Best regards,

Wolfgang Denk

Software Engineering:  Embedded and Realtime Systems,  Embedded Linux
Phone: (+49)-8142-4596-87  Fax: (+49)-8142-4596-88  Email: wd at denx.de
GUIs  are  virtually  useless.  Learn  tools.  They're  configurable,
scriptable, automatable, cron-able, interoperable, etc. We don't need
no brain-dead winslurping monolithic claptrap.
                               -- Tom Christiansen in 371140df at csnews

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