Hi Heiko,
On Wed, 31 Jul 2013 09:36:19 +0200, Heiko Schocher hs@denx.de wrote:
On the other hand, it may be hard to immediately know what functions throughout U-boot are safe to call from within board_init_f(); maybe we should start thinking about checking and marking these, the simplest way being to suffix them with "_f" once we have made sure they are safe to call from within board_init_f().
Hmmm... Maybe instead we should think (also in thinking common bring up for all boards) about:
getting rid of board_init_f in u-boot code, instead use for all boards spl code to init needed things and copy and relocate u-boot to ram in spl code ... so we have in u-boot no longer such restictions ... but thats just an idea which whirs in my head ... without thinking to deep in it.
But this approach would have some advantages ...
Well, the original SPL was basically board_init_f() plus some code to copy U-Boot from wherever it was to DDR, so it was tightly linked to board_init_f(). But... first, SPL has evolved into a "U-Boot lite" where much can happen beyond board_init_f() -- think Falcon mode, for instance -- and second, there are boards which do not have SPL at all, and their board_init_f() can thus not be "moved to SPL".
So no, I don't think we can move U-Boot's design from "_f/_r" to "SPL/U-Boot".
But we should strictly limit the scope of board_init_f() or we'll find the board_init_f()/board_init_r() pair following a patch similar to the SPL/U-Boot pair, where SPL started out as a tiny helper piece of code and ending up a resizeable (and, I dare to say, sizeable as well) kind of U-boot. If we let too many features slip in board_init_f(), it'll blur into a board_init_r() like and before we know it, it'll *require* DDR, and write access to it too...
So, board_init_() should *strictly* be limited to setting up a console (for information purposes) and giving access to DDR while in the same time never writing to it itself. Bonus points if it can limit itself to *enabling* and postpone any *optimizing*(I am thinking of DDR settings here and no, I don't have specific existing cases in mind; just sayin').
In the present instance, I'd rather we either:
- removed dependency on DT etc. by using "hard-coded" low level I2C reads for those boards that need it (I assume that for each of these boards the I2C slave, offset, and length to read are constant) in _f phase, or
But DT is used for initializing the i2c driver in tegra ...
Alright, out goes this proposal. Anyway, I didn't like it best. :)
- parsed the _f phase looking for offending functions or calls which write to .data or .bss and fix them, suffixing them with _f; in essence, that amounts to starting the implementation of my suggestion above alongside fixing the issue at hand.
The first approach is rather "let's bring the thing back up first", so it does not have my preference, but I would understand the need to quickly fix things.
Yes.
The second approach seems to be going in the same direction as Heiko's proposal of 07:52 +0200, which I thus second provided it is applicable to all the boards Wolfgang had in mind.
Lets do us this step as fixup ;-)
Alright too. :)
bye, Heiko
Amicalement,