Hi Albert,
On Tue, Jul 30, 2013 at 4:09 PM, Albert ARIBAUD albert.u.boot@aribaud.netwrote:
Hi Stephen,
On Tue, 30 Jul 2013 15:51:44 -0600, Stephen Warren swarren@wwwdotorg.org wrote:
On 07/30/2013 03:46 PM, Simon Glass wrote:
On Tue, Jul 30, 2013 at 3:32 PM, Stephen Warren <swarren@wwwdotorg.org mailto:swarren@wwwdotorg.org> wrote:
On 07/30/2013 03:21 PM, Simon Glass wrote: > On Tue, Jul 30, 2013 at 2:00 PM, Stephen Warren <swarren@wwwdotorg.org <mailto:swarren@wwwdotorg.org> > <mailto:swarren@wwwdotorg.org <mailto:swarren@wwwdotorg.org>>>wrote:
... > Oh, with the options Tegra has enabled, perhaps the call sequence is: > > board_init_f() (which uses init_sequence_f[]) -> init_func_i2c() -> > i2c_init_all(), which then calls: > > * i2c_init_board(), which is supposed to parse DT > * i2c_set_bus_num(), which will call I2C_ADAP->init > > However, according to the comments near the top of arch/arm/lib/crt0.S, > board_init_f() is called in an environment where variabledata
(.data, > .bss) is not available, hence i2c_init_board() cannotpossibly
operate > correctly since its whole purpose is to fill in variable data structures > from DT. > > > I suppose you could mark i2c_controllers so that it is in thedata
> section with __attribute__((section(".data"))). That's what eynos does, > for example. It is valid since SPL or BCT has set up the SDRAM. Neither .data nor .bss is available. Only .rodata and .text are..data is available, honest. We rely on it. During relocation it gets
copied.
It gets copied so that it ends up in RAM. It is assumed that before relocation, all .text/.rodata/.data is in ROM and can't be modified, and .bss in inaccessible. Technically that means we could read .data before relocation, but certainly not write to it.
Indeed, initialized data happens to be readable before relocation, but writing to data, on the other hand, is strictly forbidden. Before relocation, that is, while within board_init_f() the only writable area is GD.
Now in practice yes, it does work to write to .data before relocation on platforms where the U-Boot binary isn't actually in flash, but is already in ROM. However as I mention, code cannot rely on that.
Already in RAM, not ROM -- and indeed, one should not rely on this.
If any of this isn't true, then the documentation in crt0.S is wrong. I'm CC'ing Albert to see if that's the case.
In practice, perhaps we can assume that it will work on Tegrabecause we
know the DRAM is already set up, but then that makes Tegra work insome
strange special-case way, and completely violates the constraints described in crt0.S. We should be striving to unify how all the different chips work, rather than adding yet more strangespecial-cases
to the initialization sequence to hack around systemic problems.Sure, this is up to you. I was just suggesting something that works and requires little effort. It isn't pure, agreed.
The simplest approach is probably to revert the patch in question, since it clearly violates how U-Boot is supposed to work.
It's not really up to me; I think someone like Albert should make the decision since he controls the ARM U-Boot architecture, or Tom as Tegra maintainer, or perhaps you as your patch broke the code.
board_init_f() is supposed to initialize just enough of the system to allow relocation. Is initializing i2c necessary in this context?
I'm not sure. There must be some reason for those i2c_init calls in board_init_f() - or are they purely historical?
Amicalement,
Albert.
Regards, Simon