[U-Boot] [PATCH] README: Clarify use of BSS during SPL board_init_f()

[Simon Goldschmidt]

Am 08.08.2019 um 19:54 schrieb Andreas Dannenberg:
> The earlier commit....
> 
> commit a5a5d997b41a ("spl: Allow performing BSS init early before board_init_f()")
> 
> ...introduced the ability to use BSS from SPL's board_init_f() as it may
> be required in certain exceptional use cases so go ahead and update the
> README to reflect this change. Note that as highlighted with the changes
> the use of the associated CONFIG option is generally not recommended.
> 
> Signed-off-by: Andreas Dannenberg <dannenberg at ti.com>

Since I expect the patch adding CONFIG_SPL_EARLY_BSS will stay with us:

Reviewed-by: Simon Goldschmidt <simon.k.r.goldschmidt at gmail.com>


Still, I'd be very happy if someone could come up with an idea of how we 
can detect usage of BSS before board_init_r. And patches fixing such 
invalid usage would be cool as well.

Regards,
Simon

> ---
> 
> Simon, as per separate discussion thread here is a proposal for an
> update to the README. I tried to limit the changes to the what I
> thought was the most relevant section (the details section) of the
> document to strike a balance between documenting it and limiting the
> amount of attention drawn to it...
> 
> 
> --
> Andreas Dannenberg
> Texas Instruments Inc
> 
> 
> 
>   README | 7 +++++++
>   1 file changed, 7 insertions(+)
> 
> diff --git a/README b/README
> index b493ffeb2d..be3805689e 100644
> --- a/README
> +++ b/README
> @@ -267,6 +267,13 @@ board_init_f():
>   	- preloader_console_init() can be called here in extremis
>   	- should set up SDRAM, and anything needed to make the UART work
>   	- these is no need to clear BSS, it will be done by crt0.S
> +	- for specific scenarios on certain architectures an early BSS *can*
> +	  be made available (via CONFIG_SPL_EARLY_BSS by moving the clearing
> +	  of BSS prior to entering board_init_f()) but doing so is discouraged.
> +	  Instead it is strongly recommended to architect any code changes
> +	  or additions such to not depend on the availability of BSS during
> +	  board_init_f() as indicated in other sections of this README to
> +	  maintain compatibility and consistency across the entire code base.
>   	- must return normally from this function (don't call board_init_r()
>   		directly)
>   
>