Hi Dong,

Am Samstag, den 01.04.2017, 12:10 +0800 schrieb Dong Aisheng:
[...]

quoted

If we need the domains to be up before the consumers, the only
way to deal with that is to select CONFIG_PM and
CONFIG_PM_GENERIC_DOMAINS from the platform, so we have proper probe
defer handling for consumer devices of the power domains.

A bit confuse about these words...

If those options are selected we get proper PROBE_DEFER handling for
consumers of the power domain, so probe order doesn't matter.

quoted

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Personally i'd be more like Rockchip's power domain implementation.

Why?

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See:
arch/arm/boot/dts/rk3288.dtsi
drivers/soc/rockchip/pm_domains.c
Dcumentation/devicetree/bindings/soc/rockchip/power_domain.txt

How about refer to the Rockchip's way?

Why? We just changed the way how it's done for GPCv1, after more than 1
year of those patches being on the list. Why should we do it differently
for GPCv2?

Hmm?

I just thought your GPCv1 change was picked a few weeks ago (Feb 17 2017)
and there's no current users in kernel of the new binding.
That's why i come out of the idea if we could improve it before any users.

Maybe i made mistake?

The patches to change this have been out for over 1 year. I'm less than
motivated to change the binding again, after it has gone through the DT
review and has finally been picked up.

See:
commit 721cabf6c6600dbe689ee2782bc087270e97e652
Author: Lucas Stach [off-list ref]
Date:   Fri Feb 17 20:02:44 2017 +0100

    soc: imx: move PGC handling to a new GPC driver
    
    This is an almost complete re-write of the previous GPC power gating control
    code found in the IMX architecture code. It supports both the old and the new
    DT binding, allowing more domains to be added later and generally makes the
    driver easier to extend, while keeping compatibility with existing DTBs.
    
    As the result, all functionality regarding the power gating controller
    gets removed from the IMX architecture GPC driver.  It keeps only the
    IRQ controller code in the architecture, as this is closely coupled to
    the CPU idle implementation.
    
    Signed-off-by: Lucas Stach [off-list ref]
    Signed-off-by: Shawn Guo [off-list ref]

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Then it could also address our issues and the binding would be
still like:
gpc: gpc at 303a0000 {
        compatible = "fsl,imx7d-gpc";
        reg = <0x303a0000 0x1000>;
        interrupt-controller;
        interrupts = <GIC_SPI 87 IRQ_TYPE_LEVEL_HIGH>;
        #interrupt-cells = <3>;
        interrupt-parent = <&intc>;

        pgc {
                #address-cells = <1>;
                #size-cells = <0>;

                pgc_pcie_phy: power-domain at IMX7_POWER_DOMAIN_PCIE_PHY {
                        reg = <IMX7_POWER_DOMAIN_PCIE_PHY>;
                        power-supply = <&reg_1p0d>;
			clocks = <xxx>;
                };

		....
        };
};

It also drops #power-domain-cells and register domain by
one provider with multi domains which is more align with HW.

How do you think of it?

How is this more aligned with the hardware? Both options are an
arbitrary abstraction chosen in the DT binding.

GPC is a Power Controller which controls multi power domains to subsystem
by its different registers bits.
e.g. PCIE/MIPI/USB HSIC PHY.
? 0xC00 ~ 0xC3F: PGC for MIPI PHY
? 0xC40 ~ 0xC7F: PGC for PCIE_PHY
? 0xD00 ~ 0xD3F: PGC for USB HSIC PHY

So i thought it looks more like GPC is a power domain provider with multi
domains support to different subsystems from HW point of view.

Isn't that true?

Linux and hardware devices are not required to match 1:1. There is
nothing that would make subdividing a single hardware device into
multiple ones bad style.

And there's also other two concerns:
First, current genpd sysfs output still not include provider.
e.g.
root at imx6qdlsolo:~# cat /sys/kernel/debug/pm_genpd/pm_genpd_summary 
domain                          status          slaves
    /device                                             runtime status
----------------------------------------------------------------------
PU                              off-0           
    /devices/soc0/soc/130000.gpu                        suspended
    /devices/soc0/soc/134000.gpu                        suspended
    /devices/soc0/soc/2204000.gpu                       suspended
    /devices/soc0/soc/2000000.aips-bus/2040000.vpu      suspended
ARM                             off-0           

I wonder it might be a bit mess once the provider is added while each
domain is registered as a virtual provider.

The provider is a Linux device. Linux devices don't necessarily have to
correspond to hardware devices. There is no such rule.

Second, it sacrifices a bit performance when look-up PM domain in
genpd_get_from_provider if every domain is a provider.

The performance penalty of a list walk won't hurt us in the probe path,
where we are (re-)probing entire devices. There is a lot more going on
than a simple list walk.

Though it is arguable that currently only 3 domains support on MX7,
but who knows the future when it becomes much more.

However, i did see many exist users in kernel using one provider one
domain way. Maybe i'm over worried and it's not big deal.

I see that one provider with multiple domains is used more often, that
doesn't means it's necessarily better. At least I haven't hear a
convincing argument on why the chosen implementation in the GPC driver
is worse than the alternative.

Regards,
Lucas