Hi Simon,
On Thu, Jan 28, 2016 at 5:39 PM, Simon Glass sjg@chromium.org wrote:
We need a way to support more than one board per binary in U-Boot with device tree. Various methods have been discussed. The one that seems to make the most sense is to adjust SPL so that it can load a FIT which contains U-Boot and several device tree binaries. This is how things with with Linux: load a FIT and select the correct device tree to pass to Linux.
Some time ago I rise question [0] to load FIT kernel directly in SPL using falcon mode. I did look at your patches and I have a feeling that with small adaptions it should be possible? Am I right or it's impossible? (Trying to use it on am33xx boards). Many thanks.
This series:
- Adjusts the build system to optionally build a u-boot.img in FIT format
that includes the U-Boot binary and >1 device tree files
- Adjusts SPL to support loading this
- Adds a way for SPL to determine which device tree to select (by calling a
board-specific function)
- Adjusts SPL to pass this selected device tree to U-Boot when it starts
It would be painful to require an .its file for each board just to support this feature. In any case various people have commented that it would be nice not to have to write this file in general. Therefore, this series enhances mkimage to automatically generate a FIT without a .its file. So far it understands how to add a main image and a number of device tree files. It does not support hashing or verified boot as yet.
One problem with the FIT format as it stands is that all the data is inline. This means that the entire file must be read in order to figure out what device-tree files are available. It is then possible to copy the images into place.
This is not really suitable for SPL since copying can be slow, and reading unnecessary data would make the FIT format less efficient than the legacy format.
Therefore this series adds a new feature to FIT which allows the images to be stored immediately after the FIT itself ends. This makes the FIT very small. It can be read quickly and in its entirety. Then the images can be loaded one by one as needed. This allows SPL to support FITs containing lots of images very efficiently.
To achieve this, mkimage is enhanced to convert between the 'normal' and 'external' version of a FIT file. The latter is only used for the SPL loader. The main difference is that viewing an 'external' FIT will not show the contents of each image.
This series also includes a few other tidy-ups, such as moving mkimage's tricky argument-processing code to use getopt().
NOTE: There are a few problems remaining with the Kconfig conversion. I'm still fiddling with this but thought it best to send this series out for comment in the meantime.
This series is available at u-boot-fdt/spl-working.
[0] - http://lists.denx.de/pipermail/u-boot/2015-February/203938.html
U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot
BR,
marek