Re: [PATCH 00/30] ARM: OMAP2+: hwmod module clock type support

Tero Kristo
2016-04-13T06:59:50Z

On 04/12/2016 06:58 PM, Tony Lindgren wrote:
> Hi,
>
> * Rob Herring <robh@kernel.org> [160412 07:59]:
>> On Mon, Apr 11, 2016 at 11:18:51AM +0300, Tero Kristo wrote:
>>> Hi,
>>>
>>> This series transfers the hwmod clkctrl handling from the hwmod core
>>> under clock driver, the data is also transferred from hwmod data to
>>> devicetree. Done for most of the OMAP2+ platforms, except OMAP2 / OMAP3,
>>> where work is still under progress.
>>
>> Some high level questions.
>>
>> Why a DT node per clock? We've pretty much decided that is a bad idea
>> in the complex cases. TI chips certainly fall in the complex case.
>
> Well the clkctrl instances are separate independent devices under each
> clockdomain, so having a proper DT node for them makes sense to me.
>
> It's not like the clkctrl registers are just outputs of a single clock.
> A clockdomain typically has multiple inputs that are then routed in
> some combination to the clkctrl modules.
>
> I think we can group them though, here's how I'd like to set these up.
> This from dts point of view modelling omap4 TRM "3.11.16.1 WKUP_CM
> Register Summary":
>
> cm_wkup: clock@1800 { /* offset from prm_clocks at 0x4a306000 */
> ...
> reg = <0x1800 0x100>;
> ranges = <...>;
> ...
>
> gpio1_mod_ck: clock@38 {
> compatible = "ti,clock-abc";
> reg = <0x38 0x10>;
> clocks = <...>;
> ranges = <...>;
> ...
> gpio1_dbclk: clock@8 {
> #address-cells = <1>;
> #size-cells = <0>;
> ranges = <...>;
> compatible = "ti,clock-db";
> reg = <8>; /* bit offset */
> ...
> };
> };
>
> counter_32k_mod_ck: clock@50 {
> compatible = "ti,clock-xyz";
> reg = <0x50 0x10>;
> clocks = <...>;
> ...
> };
> ...
> };
>
> This then allows adding support for the clockdomain CLKSTCTRL and
> DYNAMICKDEP registers later on.
>
> Then I'd like to also have consumers be able to reference these using
> one of the two methods:
>
> 1. clocks = <&counter_32k_mod_ck>;
> 2. clocks = <&cm_wkup 0x50>;
>
> And the gpio1 debounce clock could be addressed with one of:
>
> 1. clocks = <&gpio1_dbclk>;
> 2. clocks = <&gpio1_mod_ck 8>;
>
>> You are changing compatible strings and possibly breaking compatibility.
>> Don't do that or justify why.
>
> Yes Tero please check those, we need to support the old behavior too.
> Sounds like you figured that out how to do that alreadey by generating
> the clock name for the built-in data.

Some of the old clock nodes are being dropped by this series, namely the
timer ones, and they are getting merged to the new timerX_mod_ck nodes.

The reason for this is the behavior of the clock driver itself; it
assumes it gets a clock handle for which it can do clk_set_parent (for
setting proper source clock to get correct time-base), but normal
_mod_ck nodes do not support this. So, what happens for example for
omap4 is following:

old:
dmt1_clk_mux: dmt1_clk_mux@1840 {
#clock-cells = <0>;
compatible = "ti,mux-clock";
clocks = <&sys_clkin_ck>, <&sys_32k_ck>;
ti,bit-shift = <24>;
reg = <0x1840>;
};

=> becomes a mux clock

new:
timer1_mod_ck: timer1_mod_ck@1840 {
#clock-cells = <0>;
compatible = "ti,omap4-sw-mux-mod-clock";
reg = <0x1840>, <0x1840>;
clocks = <&sys_clkin_ck>, <&sys_32k_ck>;
ti,bit-shift = <24>;
};

=> becomes a composite clock with gate and mux components

These clocks are then directly referenced by hwmod. The reason for
having two registers under the new timer node is that in some hardwares
(like AM33xx), the register address for the gate and mux component are
different.

Anyway, compatibility will be broken once the hwmod_data changes go in
for individual SoCs, as the clkctrl portion is going to be dropped, and
the hwmod has no chance to work with old DT data. If this is not
acceptable, then the whole exercise becomes moot as we need to move the
data someplace else within the kernel, and forget about the transition
to DT.

-Tero