[U-Boot] [RFC PATCH 00/11] extend FIT loading support (plus Pine64/ATF support)

[André Przywara]

On 27/01/17 21:29, Simon Glass wrote:

Hi Simon,

> On 19 January 2017 at 18:53, Andre Przywara <andre.przywara at arm.com> wrote:
>> Currently the FIT format is not used to its full potential in the SPL:
>> It only loads the first image from the /images node and appends the
>> proper FDT.
>> Some boards and platforms would benefit from loading more images before
>> starting U-Boot proper, notably Allwinner A64 and ARMv8 Rockchip boards,
>> which use an ARM Trusted Firmware (ATF) image to be executed before U-Boot.
>>
>> This series tries to solve this in a board agnostic and generic way:
>> We extend the SPL FIT loading scheme to allow loading multiple images.
>> So apart from loading the image which is referenced by the "firmware"
>> property in the respective configuration node and placing the DTB right
>> behind it, we iterate over all strings in the "loadable" property.
>> Each image referenced there will be loaded to its specified load address.
>> The entry point U-Boot eventually branches to will be taken from the
>> first image to explicitly provide the "entry" property, or, if none
>> of them does so, from the load address of the "firmware" image.
>> This keeps the scheme compatible with the FIT images our Makefile creates
>> automatically at the moment.
>>
>> Apart from the already mentioned ATF scenario this opens up more usage
>> scenarios, of which the commit message of patch 04/11 lists some.
>>
>> The first three patches rework the SPL FIT support to be more flexible
>> and to allow easier usage in the fourth patch, which introduces the
>> multiple-image loading facility.
>> The remaining patches enable that support for the Pine64 board to make
>> its SPL support finally useful and to demonstrate usage of this scheme:
>> patches 5-7 extend the usable SPL size by about 4 KB to allow AArch64
>> compilation of the SPL with FIT support enabled. Patch 8 implements the
>> board selector routine, which selects either the Pine64 or Pine64+ DTB
>> depending on the detected DRAM size. Patch 9 enables SPL FIT support in
>> the Pine64 defconfig.
>> To demonstrate the usage, patch 10 provides a FIT source file, which
>> loads and executes ATF before the U-Boot proper. Users are expected to
>> compile this with "mkimage -f boards/sunxi/pine64_atf.its -E pine64.itb",
>> then write the resulting file behind the SPL on an SD card (or any other
>> U-Boot supported boot media, for that matter).
>> Patch 11 then adds FIT support to the sunxi SPL SPI loading routine,
>> which allows to load ATF on boards with SPI flash as well.
>>
>> Questions:
>> 1) Is this scheme the right one (usage of "firmware" and "loadables",
>>    determination of entry point)? Shall we make use of the "setup"
>>    property?
> 
> Seems reasonable to me.
> 
>> 2) Shall we extend mkimage to allow supplying "loadable" files on the
>>    command line, which would allow to build the .itb file automatically?
> 
> Yes.

I was thinking about this a bit more, as Andrew pointed out before it
may become hairy to add tons of options to mkimage.
I came up with a simple shell script, mostly using here documents
(cat << _EOF) to generate the .its file on the fly, adding all DTs given
on the command line. It's pretty easy, yet readable and adaptable. So
each platform could provide one, if needed, and could hard code things
like ATF in here.

>> 3) Is providing the .its source file for a (family of) boards the right
>>    way?
> 
> Where needed (i.e. the mkimage command line is not trivial)
> 
>> 4) Does this break any boards which already use SPL FIT loading?
> 
> Probably not, but I'm sure it would be spotted if so.
> 
>>
>> And for the Pine64 part:
>> 5) Is extending the usable SPL size like in patch 5-7 acceptable?
>>
>> I have a more generic solution for the .dtb selection in mind: Based on
>> some patch from Siarhei we store the .dtb filename in the SPL header and
>> select the .dtb from the FIT image by simply matching the name. This would
>> allow _one_ build supporting multiple boards. The actual board name would
>> need to written into the SPL header or could be copied from there when
>> updating the image.
>> I can provide the patches once we agreed upon this series.
>>
>> Please let me know what you think!
> 
> I think it is a nice piece of work. You might want to make the new
> feature optional if it saves code space.
> 
> FIT is preferable to a raw binary image. There is also binman which
> can create binary images with things placed as you wish, but it's best
> to use FIT where you can.

Yeah, in this case it is not so much about placing, but more about
flexibility, so FIT is really nice here.
I am also looking at a firmware update tool atm, having FIT would allow
to update single components only - for instance just the .dtb.

> A few more things:
> 
> - Can you make sure that your new node structure is clearly documented
> (with an example) in doc/uImage.FIT/ ?

Yes, sure.

> - Can you add a pytest for sandbox_spl, which verifies that everything
> is loaded correctly? As an alternative I suppose you could adjust
> test-fit.py (which should move to pytest)

OK, will look into this.

Thanks for the comments!

Cheers,
Andre.