[U-Boot] [PATCH v2 1/2] Add README for the "Falcon" mode

[Stefano Babic <sbabic@denx.de>]

On 14/11/2012 11:29, Otavio Salvador wrote:
> 
> 

Hi Otavio,

> 
> In the text you have the offset to save the image onto a NAND offset so
> I fail to see how it'd be used for SD-Card.
> 
> Can you elaborate it a bit?

No, I can't without introducing errors. Current code supports Falcon
only booting from NAND - I do not think that it is a big thing to use
another media, but it is not yet done. This document must

>     +and can be generalized seen as a way to start an image performing
>     the minimum
>     +required initialization. SPL initializes mainly the RAM controller,
>     and after
>     +that copies U-Boot image into the memory. The "Falcon" mode extends
>     this way
>     +allowing to start the Linux kernel directly from SPL. A new command
>     is added
>     +to U-Boot to prepare the parameters that SPL must pass to the
>     kernel, using
>     +ATAGS or Device Tree.
>     +
>     +Falcon adds a command under U-Boot to reuse all code responsible to
>     prepare
>     +the interface with the kernel. In usual U-boot systems, these
>     parameters are
>     +generated each time before loading the kernel, passing to Linux the
>     address
>     +in memory where the parameters can be read.
>     +With falcon, this snapshot can be saved into persistent storage and
>     SPL is
>     +informed to load it before running the kernel.
> 
> 
> You mix Falcon and falcon.

You're right, there are already comments about this. This will be fixed
globally in V3 (I will use Falcon Mode consistently).

> I'd say you always use Falcon as it is the
> name of the feature so it ought to be in upper case. Another thing,
> 'With falcon, ' ought to be move to the previous line or have an empty
> line before it.

Ok

>  
> 
>     +To boot the kernel, these steps under a Falcon-aware U-Boot are
>     required:
>     +
>     +1. Boot the board into U-Boot.
>     +Use the "spl export" command to generate the kernel parameters area
>     or the DT.
>     +U-boot runs as when it boots the kernel, but stops before passing
>     the control
>     +to the kernel.
>     +
>     +2. Saves the prepared snapshot into persistent media.
>     +The address where to save it must be configured into board
>     configuration
>     +file (CONFIG_CMD_SPL_NAND_OFS for NAND).
> 
> 
> And for others?

Not yet implemented, patches welcome ! But you are right, there is
already a patch to use a NOR flash that should flow soon into mainline.
I will check and add documentation for it. For the orher media, the
document must be updated together when they will be full supported.


>  
> 
>     +3. Boot the board into "Falcon" mode. SPL will load the kernel and copy
>     +the parameters area to the required address.
>     +
>     +It is required to implement a custom mechanism to select if SPL
>     loads U-Boot
>     +or another image.
>     +The value of a GPIO is a simple way to operate the selection, as
>     well as
>     +reading a character from the SPL console if CONFIG_SPL_CONSOLE is set.
> 
> 
> An empty line before "The value"?

Ok

Best regards,
Stefano Babic

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