Hi Stephen,

On 2016-09-13 00:28, Stephen Boyd wrote:

On 09/12, Marek Szyprowski wrote:

quoted

On 2016-09-08 02:22, Stephen Boyd wrote:

quoted

On 09/01, Marek Szyprowski wrote:

quoted

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 <redacted>
---
  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?

Is that even possible? Every device should be in some power
domain, even if it's just an "always on" power domain that we
don't really control from software.

Right now none dts of which I'm aware of doesn't define the power domain for
the parts of the SoC, which are always on and doesn't need any additional
management.

quoted

The question is how the automated assignment to domains would be handled for
such case?

I don't get this part. Do you mean how we indicate to the driver
which power domain to use at the right time?

This was about Linux device core, which assigns device to its power domain
and ensures that the power domain is in right state during device probe and
then during device operation. Currently core supports only one domain per
device, so the question was which domain to chose if there are more than
one listed.

quoted

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.

Right. Runtime PM will need to be improved to allow this case.

quoted

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

         clock: clock-controller@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.

Ok. From a DT perspective the sub-nodes seem to be a workaround
for how the linux device model is mapped to power domains. I'm
not sure we want to make subnodes in the clk controller just to
make sub devices that we can target from the clk registration
path. Those sub nodes aren't devices at all. I understand why
it's being done this way, I just don't see how it fits into DT
design methodologies.

I don't think that using sub-nodes for describing details of the given
hardware block is something uncommon in DT. Please check pin control
or PMICs (especially regulator providers). Same for various "port"
sub-nodes often used by various video/display devices and bridges.

The above presented method describes well which sub-part of clock
controller is placed in which power domain.

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

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