Remove the workaround code from fel-sdboot.c (and possibly uart0-helloworld)

[n1tehawk]

The root cause of the problems that surfaced with these ARM binaries is that the U-Boot mksunxiboot utility writes a minimal header that is too small to avoid corruption of actual code by the BROM bootloader. See https://patchwork.ozlabs.org/patch/622173.

Once this is fixed (in upstream U-Boot), we should probably revert the NOP padding used in fel-sdboot.c to circumvent this. The uart0-helloworld-sdboot.sunxi under development currently also contains a workaround that won't be needed any more afterwards.

[ssvb]

Yes, the workaround needs to be at least changed to branch over the corrupted location. The description at

sunxi-tools/fel-sdboot.c

Lines 41 to 50 in ce9cf33

	/*
	* FEL mode fails to activate in an unpredictable way without
	* this NOP padding. Minor changes in the code, such as checking
	* the PC register (PC >= 0x10000) instead of SCTLR.V or doing
	* jump instead of call to the FEL handler in the BROM sometimes
	* break on A64 and sometimes break on A10/A13/A20. Trying to
	* add DSB & ISB instructions and/or invalidating caches and
	* BTB do not seem to make any difference. Only adding a bunch
	* of NOP instructions in the beginning helps.
	*/

also needs to be updated. It did accurately state the facts, but now we have more information.

As for removing the workaround completely, some people may still try to recompile these binaries and use a buggy mksunxiboot tool while doing this. It might be safer to keep the workarounds at least for a year or so, maybe even longer.

[n1tehawk]

Okay, i'll tag this as "wontfix" for the time being - so the issue can be left open until we decide that a sane mksunxiboot should have made it everywhere, and the workaround gets finally removed.

[n1tehawk]

Note: U-Boot release v2016.07 contains the related commit that fixes SPL header size, and thus mksunxiboot operation. Images created with this (or a later) version account for the field written by the BROM, i.e. they should no longer suffer from code corruption.