On Fri, 27 Feb 2015 16:39:45 +0000 Ian Campbell ijc+uboot@hellion.org.uk wrote:
On Tue, 2015-02-24 at 04:48 +0200, Siarhei Siamashka wrote:
In order to fully support booting the whole system over USB OTG without relying on anything else (MMC, SATA, USB sticks, ...), it is possible to upload the 'boot.scr' file to DRAM using the 'fel' tool. But U-Boot still needs to be able to pick it up there before checking any other boot media.
Signed-off-by: Siarhei Siamashka siarhei.siamashka@gmail.com
The patch might be not the best way to implement this. But it would be great if U-Boot had out of the box support for: http://linux-sunxi.org/index.php?title=FEL/USBBoot&oldid=13134#Boot_the_...
One of the bad things about this patch is that the "scriptaddr" variable needs to be hardcoded and protected agaist modifications (if this address is to be used from the SPL).
Perhaps use a separate dedicated/hardcoded address for the FEL boot script to avoid adding unusual semantics to $scriptaddr (which might surprise users not using fel)?
Making something that is FEL-boot specific and diverges from the normal configuration is not great. Is there a real practical need for anyone to override $scriptaddr and the other similar variables in the environment? If not, marking them as read-only (similar to how the MAC address is handled) may be a reasonable solution.
If the FEL address has to be 0x43100000 for compatibility with existing instructions/tools that might mean moving the current scriptaddr elsewhere. I think we can live with that.
There was an idea to make mksunxiboot tool store all these magic addresses into the bootable image, so that the fel tool could find them there. Some of such ideas are listed here:
http://linux-sunxi.org/FEL/USBBoot#Potential_future_improvements_for_u-boot_...
This can only work if these addresses become compile time constants and can't be overridden by the environment. If the user really has a good reason to change them, making them configurable via menuconfig may be a solution.
Also I'm not sure how this all could fit into the "config_distro_bootcmd.h" model, so I even have not tried that yet.
Just at a quick glance, based on the PXE entry something like:
#define BOOTENV_DEV_FEL(devtypeu, devtypel, instance) \ "bootcmd_fel=source ...\0"
i.e. all the magic params are irrelevant in this case. Perhaps "bootcmd_"#devtypel"=...\0" but I don't think that's needed in this instance. BOOTENV_DEV_PXE doesn't bother at least.
Then in BOOT_TARGET_DEVICES include "func(FEL, fel, na)"
Well, in fact I'm not a big fan of the C preprocessor based approach used there. And if I understand it correctly, this is already causing some troubles for the A80 (sun9i) support:
https://patchwork.ozlabs.org/patch/429463/
The C preprocessor surely can be used, but such code is barely maintainable.
IMHO all the necessary adjustments to the environment variables can be done at runtime in the misc_init_r() function. For example, pre-pending "fel" to the "boot_targets" variable can be done based on a runtime check and activated only for the FEL mode. The C preprocessor constants are much less flexible.