[PATCH 4/5] ARM: dts: exynos: add support for ISP power domain to exynos4x12 clocks device

[Marek Szyprowski]

Hi Stephen,


On 2016-09-08 02:22, Stephen Boyd wrote:
> On 09/01, Marek Szyprowski wrote:
>> Exynos4412 clock controller contains some additional clocks for FIMC-ISP
>> (Camera ISP) subsystem. Registers for those clocks are partially located
>> in the SOC area, which belongs to ISP power domain.
>>
>> This patch extends clock controller node with ISP clock sub-node and link
>> (phandle) to ISP power domain.
>>
>> Signed-off-by: Marek Szyprowski <m.szyprowski at samsung.com>
>> ---
>>   arch/arm/boot/dts/exynos4x12.dtsi | 5 +++++
>>   1 file changed, 5 insertions(+)
>>
>> diff --git a/arch/arm/boot/dts/exynos4x12.dtsi b/arch/arm/boot/dts/exynos4x12.dtsi
>> index 3394bdcf10ae..4daea67546b9 100644
>> --- a/arch/arm/boot/dts/exynos4x12.dtsi
>> +++ b/arch/arm/boot/dts/exynos4x12.dtsi
>> @@ -74,6 +74,11 @@
>>   		compatible = "samsung,exynos4412-clock";
>>   		reg = <0x10030000 0x20000>;
>>   		#clock-cells = <1>;
>> +
>> +		isp-clock-controller {
>> +			compatible = "samsung,exynos4412-isp-clock";
>> +			power-domains = <&pd_isp>;
>> +		};
> Why can't we extend support in power domains code to have
> multiple domains for a single device node? i.e. power-domains =
> <&pd_isp>, <&pd_foo>, <&pd_bar>, and then pick the right one with
> power-domain-names or something like that? Making a subnode
> (which seems to turn into a child platform device?) seems like a
> quick solution for larger problems.

The larger problem here is the fact that clock controller is partially 
located
in different power areas of SoC. Majority of the clock controllers is 
located
in the area which is typically always powered (besides system sleep case),
while a few Camera ISP registers are located in the ISP block, which have
separate power domain. Having a separate nodes for sub-parts of the 
device is
rather common approach, already practices by some more complex devices.

I see some serious design problems with multiple entries in power domains
property. First how to show that some part of the device IS NOT in any 
domain?
The question is how the automated assignment to domains would be handled for
such case?

The second is related to Linux kernel internals. Right now device 
drivers are
not aware of the power domains - there are no direct calls to power domains
code, everything is hidden behind runtime pm which does all the hard work.

Similar situation is on Exynos 542x/5800, which will look more or less like
this:

         clock: clock-controller at 10010000 {
              compatible = "samsung,exynos5420-clock";
              reg = <0x10010000 0x30000>;
              #clock-cells = <1>;
+
+            gsc-clock-controller {
+                 compatible = "samsung,exynos5420-gsc-clock";
+                 power-domains = <&gsc_pd>;
+            };
+
+            isp-clock-controller {
+                 compatible = "samsung,exynos5420-isp-clock";
+                 power-domains = <&isp_pd>;
+            };
+
+            mfc-clock-controller {
+                 compatible = "samsung,exynos5420-mfc-clock";
+                 power-domains = <&mfc_pd>;
+            };
+
+            msc-clock-controller {
+                 compatible = "samsung,exynos5420-msc-clock";
+                 power-domains = <&msc_pd>;
+            };
+
+            disp-clock-controller {
+                 compatible = "samsung,exynos5420-disp-clock";
+                 power-domains = <&disp_pd>;
+            };
          };

The patch is not yet ready, so I didn't include it in this patchset.

The clock controller evolved and in the latest Exynos 5433 it is divided in
several parts (each related to given hw block and its power domains), which
each is now modeled by a separate device node. This allows to bind power
domains cleanly without any need for sub-nodes for the clock controllers.

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland