[Letux-kernel] ARM: OMAP2+: reset controller support

[H. Nikolaus Schaller]

Hi Tero,

> Am 31.10.2016 um 13:57 schrieb Tero Kristo <t-kristo at ti.com>:
> 
> On 29/10/16 12:30, H. Nikolaus Schaller wrote:
>> Hi,
>> I am trying to fix some parts in the OMAP3 SGX drivers for the latest kernels
>> and came across the problem that the reset framework core is now assuming DT
>> support. This means we need some reset controller driver for the OMAP3.
>> 
>> Then I found your patch series "[PATCH 00/17] ARM: OMAP2+: reset controller support"
>> from last year and it appears to be the missing piece.
>> 
>> I have not found it in linux-next so I wonder what happened to it.
> 
> The old reset controller work was abandoned,

Ah, I see.

Indeed it makes not much sense to just handle the reset-controller but
not other hwmods.

> and it won't be resurrected before we have:
> 
> a) hwmod clock driver merged (which is under reviews atm)
> b) OMAP interconnect driver merged (which is under work by Tony)

This might take more time than I want to wait.

> 
> I believe you need to introduce platform data callbacks for reset handling until this is resolved, and call hwmod reset functionality directly.

If possible, I would prefer just to take your reset-controller as
a temporary solution, because we don't have a platform driver any
more or it will become a really ugly hack.

What I have tried to so far is:

1. applied to v4.3:
	- works well (or at least not recognizably different)
	- device boots
2. rebased to v4.9-rc2:
	- needed some manual rebase which I hope I have done correctly.
	- also needs some fixes for "new" SoC which interfere.
	- But OMAP3 hangs at "Starting kernel...".
	- bisect shows that "ARM: OMAP2+: hwmod: parse reset information from DT" triggers the problem.
	- I can make the kernel boot if I return 0 by _init_resets() - but then of course the resets
	  don't work well and report "missing rc".

What I am also not sure (also in case of platform driver) is which register carries the SGX_RST.

TRM mentions it:

"Software controls the release of SGX_RST using the PRCM.RM_RSTCTRL_SGX[0] SGX_RST bit."

but does not tell the register address or bit number. But maybe I can locate that in some older
TI kernel or SGX driver.

And I think I have to add the proper resets = <&prm ...> values which are not really well
documented, but I think I understand them.

Anyways if you want to take a look into my attempt to rebase:

	https://github.com/goldelico/gta04-kernel/commits/work/test/omap/reset-cont-v4.9

BR and thanks,
Nikolaus