[U-Boot] [PATCH 00/27] spl: Use linker list and parameters for SPL image loading

[Simon Glass]

Hi Tom,

On 18 September 2016 at 16:14, Tom Rini <trini at konsulko.com> wrote:
> On Sun, Sep 18, 2016 at 01:44:49PM -0600, Simon Glass wrote:
>
>> At present the SPL code uses a global spl_image variable which is shared
>> amongst lots of files, some in common/spl and some elsewhere. There is no
>> need for this to be global, and in fact a parameter makes it easier to
>> understand what information the functions act on. It also reduces the BSS
>> use in the SPL (at the expense of stack) which is useful on boards which
>> don't have BSS available early on.
>
> Thanks for taking a stab at cleaning this up.

I ran into it with the 64-bit x86 stuff and decided to take a detour :-)

>
> [snip]
>> There is a priorty value attached to each loader which should allow the
>> existing ordering to be maintained.
>
> I worry here about some of the corner cases, but it's probably no more
> or less fragile than currently at least.  I'm actually not sure how
> that's working in this version of the series, everyone gets priority 0
> filled in so it seems like we're on linker order.  But I'm also not
> convinced that it's a problem here.  As far as I can recall, the use
> cases are that a given binary will support say NAND and MMC, and at run
> time knows that it came from NAND or MMC, and thus we need to look at
> the same device for U-Boot itself.  So order doesn't matter there.  So
> we can just drop that part I think.

I see in the code that if Ubifs is enabled, it uses that instead of
NAND and ONENAND. There is another case too - SPI might have a
board-specific loader which takes precedence (although I suspect in
the sunxi case the generic loader is not present).

If these are not needed then we can drop it.

At present priority is handled by adding the priority value into the
linker list element name. Since they are sorted in order within the
image, this gives the required result.

>
>> Code size is about 20 bytes larger on average which I think is acceptable.
>> The BSS size drops by about 64 bytes, but really this just transfers to
>> the stack.
>
> How about the worst case growths in what we have today?

Ah well that's something buildman cannot tell me! There is a small
overhead for the lookup code (about 20-30 bytes) and 8-12 bytes for
each loader method. Here's the buildman summary.

$ buildman -b spl -s --step 0 -S
boards.cfg is up to date. Nothing to do.
Summary of 2 commits for 1196 boards (32 threads, 1 job per thread)
01: Makefile: Give a build error if ad-hoc CONFIG options are added
  blackfin:  +   cm-bf527 bf609-ezkit bf537-stamp
     sparc:  +   grsim grsim_leon2 gr_cpci_ax2000 gr_xc3s_1500 gr_ep2s60
     nios2:  +   10m50 3c120
microblaze:  +   microblaze-generic
  openrisc:  +   openrisc-generic
28: spl: Make spl_boot_list a local variable
   aarch64: (for 51/51 boards)  spl/u-boot-spl:all +36.8
spl/u-boot-spl:bss -6.3  spl/u-boot-spl:data +5.6
spl/u-boot-spl:rodata +7.5  spl/u-boot-spl:text +29.9
   powerpc: (for 415/415 boards)  spl/u-boot-spl:all -24.7
spl/u-boot-spl:bss -0.1  spl/u-boot-spl:data -0.1
spl/u-boot-spl:rodata -15.9  spl/u-boot-spl:text -8.6
   sandbox: (for 3/3 boards)  spl/u-boot-spl:all +37.3
spl/u-boot-spl:bss -10.7  spl/u-boot-spl:rodata +10.7
spl/u-boot-spl:text +37.3
       arm: (for 552/552 boards)  all -0.8  bss -0.8  data -0.1
spl/u-boot-spl:all -66.3  spl/u-boot-spl:bss -22.3
spl/u-boot-spl:data -5.1  spl/u-boot-spl:rodata +0.5
spl/u-boot-spl:text -39.3

>
>> There is an obvious follow-on from this, to move boot_name_table[] into the
>> same linker list struct (i.e. add a name field to struct spl_image_loader).
>> The complication here is that we don't want naming if
>> CONFIG_SPL_LIBCOMMON_SUPPORT is not enabled, since it bloats the code. In
>> addition I think that common/spl/spl.c can be tidied up a little.
>
> Yeah, I worry about size growth in doing that too.  But maybe we can be
> a little clever when declaring the ll and just not have the strings if
> !LIBCOMMON ?

Yes I think so...perhaps someone else might take a look, or I'll wait
for a rainy day!

Regards,
Simon