[U-Boot-Users] dynamic setting of CONFIG_SYS_CLK_FREQ

Wolfgang Denk
2004-04-26T09:14:53Z

In message <408CC565.9040006@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
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