[U-Boot] [PATCH v7 13/19] Makefile: u-boot-with-spl.bin: Fix SPL padding

[Benoît Thébaudeau]

On Monday, February 18, 2013 7:24:51 PM, Scott Wood wrote:
> On 02/18/2013 12:22:58 PM, Benoît Thébaudeau wrote:
> > On Monday, February 18, 2013 7:02:49 PM, Scott Wood wrote:
> > > On 02/18/2013 12:00:52 PM, Benoît Thébaudeau wrote:
> > > > The only question is if we may need to have an empty gap between
> > the
> > > > SPL and
> > > > U-Boot within the resulting image. I don't think so since that
> > would
> > > > mean that
> > > > the target memory device has an area that is not really available
> > at
> > > > the
> > > > location of this gap.
> > >
> > > Why not allow that possibility?
> > 
> > To save a config setting (there are already many for SPL) if this is
> > not
> > strictly required, but also for the reason below.
> > 
> > >  Maybe it's easier for the SPL to load
> > > from a particular offset (e.g. NAND starting at the beginning of a
> > > block)?
> > 
> > CONFIG_SPL_MAX_SIZE would be closer to a NAND mapping in that case
> > (e.g. size of
> > 1 NAND Flash block) than CONFIG_SPL_PAD_TO (address within RAM that
> > should be
> > considered relatively to CONFIG_SPL_TEXT_BASE to get the NAND offset).
> 
> CONFIG_SPL_PAD_TO is for the placement of the payload

Correct.

> -- and it's not a
> RAM address.

It doesn't have to be, but it may be for some configs.

>  Currently it is a link address (or zero if the linker
> script handles padding, or padding is not required for other reasons).

Correct.

> With your patch it it is a file offset, IIUC.

With my patch, it is nothing at all since only CONFIG_SPL_MAX_SIZE is used.

> CONFIG_SPL_MAX_SIZE is what it says -- the maximum size that the SPL
> may be, ideally to be enforced by the linker script.

Correct.

> They are different.  An SPL wanting the payload to begin as a block
> boundary does not mean the hardware is suddenly capable of loading an
> entire block of SPL.

Sure, but my question is: Why would you want to have a 2-kiB SPL followed by a
126-kiB gap before the payload? Why couldn't you place the payload on the 1st
page boundary after the SPL?

If there are hardware constraints or something that make CONFIG_SPL_PAD_TO
useful in some cases, then let's use it, but otherwise, why keep it?

And if we keep it, do we change it to an image offset, or do we keep it as a
link address?

> > Also, CONFIG_SPL_PAD_TO and CONFIG_SPL_MAX_SIZE depend on each other:
> > If both
> > can be defined, you may change one forgetting the other one, which
> > could e.g.
> > result in an overlapping of SPL and U-Boot that won't show up at
> > build time
> > (with CONFIG_SPL_MAX_SIZE = 0x1000 and CONFIG_SPL_PAD_TO =
> > CONFIG_SPL_TEXT_BASE
> > + 0x800, the SPL would build fine, and objcopy wouldn't complain).
> 
> So add a check that CONFIG_SPL_PAD_TO >= CONFIG_SPL_MAX_SIZE (assuming
> the new interpretation of CONFIG_SPL_PAD_TO as a file offset), and let
> CONFIG_SPL_PAD_TO default to CONFIG_SPL_MAX_SIZE if not set.

That would make sense. The current default value of 0 for CONFIG_SPL_PAD_TO does
not make sense since it means that the SPL can't know where the payload is
located within the image.

Best regards,
Benoît