Message-Id: <20241211-b4-linux-next-24-11-18-clock-multiple-power-domains-v8-3-5d93cef910a4@linaro.org>
Date: Wed, 11 Dec 2024 16:54:34 +0000
From: Bryan O'Donoghue <bryan.odonoghue@...aro.org>
To: Bjorn Andersson <andersson@...nel.org>, 
 Michael Turquette <mturquette@...libre.com>, 
 Stephen Boyd <sboyd@...nel.org>, 
 Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc: linux-arm-msm@...r.kernel.org, linux-clk@...r.kernel.org, 
 linux-kernel@...r.kernel.org, Bryan O'Donoghue <bryan.odonoghue@...aro.org>
Subject: [PATCH v8 3/3] clk: qcom: Support attaching GDSCs to multiple
 parents

When a clock-controller has multiple power-domains we need to attach the
GDSCs provided by the clock-controller to each of the list of power-domains
as power subdomains of each of the power-domains respectively.

GDSCs come in three forms:

1. A GDSC which has no parent GDSC in the controller and no child GDSCs.
2. A GDSC which has no parent GDSC in the controller and has child GDSCs.
3. A child GDSC which derives power from the parent GDSC @ #2.

Cases 1 and 2 are "top-level" GDSCs which depend on the power-domains - the
power-rails attached to the clock-controller to power-on.

When dtsi::power-domains = <> points to a single power-domain, Linux'
platform probe code takes care of hooking up the referenced power-domains
to the clock-controller.

When dtsi::power-domains = <> points to more than one power-domain we must
take responsibility to attach the list of power-domains to our
clock-controller.

An added complexity is that currently gdsc_enable() and gdsc_disable() do
not register the top-level GDSCs as power subdomains of the controller's
power-domains.

This patch makes the subdomain association between whatever list of
top-level GDSCs a clock-controller provides and the power-domain list of
that clock-controller.

What we don't do here is take responsibility to adjust the voltages on
those power-rails when ramping clock frequencies - PLL rates - inside of
the clock-controller.

That voltage adjustment should be performed by operating-point/performance
setpoint code in the driver requesting the new frequency.

There are some questions that it is worth discussing in the commit log:

1. Should there be a hierarchy of power-domains in the clock-controller ?

   In other words if a list of dtsi::power-domains = <pd_a, pd_b, ..>
   should a specific hierarchy be applied to power pd_a then pd_b etc.

   It may be appropriate to introduce such a hierarchy however reasoning
   this point out some more, any hierarchy of power-domain dependencies
   should probably be handled in dtsi with a chain of power-domains.
   One power-domain provider would point to another via
   dtsi::power-domains = <>.

   For the case of GDSC on/off there is no clear use-case to implement
   a mechanism for a dependency list in the GDSC logic in-lieu of already
   existing methods to do dependencies in dtsi::power-domains = <>.

   A defacto ordering happens because the first power-domain pd_a will be
   powered before pd_b as the list of domains is iterated through linearly.

   This defacto hierarchical structure would not be reliable and should
   not be relied upon.

   If you need to have a hierarchy of power-domains then structuring the
   dependencies in the dtsi to

   Do this:

   pd_a {
	compat = "qcom, power-domain-a";
        power-domains = <&pd_c>;
   };

   pd_b {
        compat = "qcom, power-domain-b";

   };

   pd_c {
        compat = "qcom, power-domain-c";
   };

   clock-controller {
       compat ="qcom, some-clock-controller";
       power-domains = <&pd_a, &pd_b>;
   }

   Not this:

   pd_a {
	compat = "qcom, power-domain-a";
   };

   pd_b {
        compat = "qcom, power-domain-b";

   };

   pd_c {
        compat = "qcom, power-domain-c";
   };

   clock-controller {
       compat ="qcom, some-clock-controller";
       power-domains = <&pd_c, &pd_a, &pd_b>;
   }

   Thus ensuring that pd_a directly references its dependency to pd_c
   without assuming the order of references in clock-controller imparts
   or implements a deliberate and specific dependency hierarchy.

2. Should each GDSC inside a clock-controller be attached to each
   power-domain listed in dtsi::power-domains = <> ?

   In other words should child GDSCs attach to the power-domain list.

   The answer to this is no. GDSCs which are children of a GDSC within a
   clock-controller need only attach to the parent GDSC.

   With a single power-domain or a list of power-domains either way only
   the parent/top-level GDSC needs to be a subdomain of the input
   dtsi::power-domains = <>.

3. Should top-level GDSCs inside the clock-controller attach to each
   power-domain in the clock-controller.

   Yes a GDSC that has no parent GDSC inside of the clock-controller has an
   inferred dependency on the power-domains powering the clock-controller.

4. Performance states
   Right now the best information we have is that performance states should
   be applied to a power-domain list equally.

   Future implementations may have more detail to differentiate the option
   to vote for different voltages on different power-domains when setting
   clock frequencies.

   Either way setting the performance state of the power-domains for the
   clock-controller should be represented by operating-point code in the
   hardware driver which depends on the clocks not in the
   gdsc_enable()/gdsc_disable() path.

Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@...aro.org>
---
 drivers/clk/qcom/common.c |  1 +
 drivers/clk/qcom/gdsc.c   | 35 +++++++++++++++++++++++++++++++++++
 drivers/clk/qcom/gdsc.h   |  1 +
 3 files changed, 37 insertions(+)

diff --git a/drivers/clk/qcom/common.c b/drivers/clk/qcom/common.c
index b79e6a73b53a4113ca324d102d7be5504a9fe85e..9e3380fd718198c9fe63d7361615a91c3ecb3d60 100644
--- a/drivers/clk/qcom/common.c
+++ b/drivers/clk/qcom/common.c
@@ -323,6 +323,7 @@ int qcom_cc_really_probe(struct device *dev,
 		scd->dev = dev;
 		scd->scs = desc->gdscs;
 		scd->num = desc->num_gdscs;
+		scd->pd_list = cc->pd_list;
 		ret = gdsc_register(scd, &reset->rcdev, regmap);
 		if (ret)
 			return ret;
diff --git a/drivers/clk/qcom/gdsc.c b/drivers/clk/qcom/gdsc.c
index 4fc6f957d0b846cc90e50ef243f23a7a27e66899..cb4afa6d584899f3dafa380d5e01be6de9711737 100644
--- a/drivers/clk/qcom/gdsc.c
+++ b/drivers/clk/qcom/gdsc.c
@@ -506,6 +506,36 @@ static int gdsc_init(struct gdsc *sc)
 	return ret;
 }
 
+static int gdsc_add_subdomain_list(struct dev_pm_domain_list *pd_list,
+				   struct generic_pm_domain *subdomain)
+{
+	int i, ret;
+
+	for (i = 0; i < pd_list->num_pds; i++) {
+		struct device *dev = pd_list->pd_devs[i];
+		struct generic_pm_domain *genpd = pd_to_genpd(dev->pm_domain);
+
+		ret = pm_genpd_add_subdomain(genpd, subdomain);
+		if (ret)
+			return ret;
+	}
+
+	return 0;
+}
+
+static void gdsc_remove_subdomain_list(struct dev_pm_domain_list *pd_list,
+				       struct generic_pm_domain *subdomain)
+{
+	int i;
+
+	for (i = 0; i < pd_list->num_pds; i++) {
+		struct device *dev = pd_list->pd_devs[i];
+		struct generic_pm_domain *genpd = pd_to_genpd(dev->pm_domain);
+
+		pm_genpd_remove_subdomain(genpd, subdomain);
+	}
+}
+
 int gdsc_register(struct gdsc_desc *desc,
 		  struct reset_controller_dev *rcdev, struct regmap *regmap)
 {
@@ -558,6 +588,9 @@ int gdsc_register(struct gdsc_desc *desc,
 			ret = pm_genpd_add_subdomain(scs[i]->parent, &scs[i]->pd);
 		else if (!IS_ERR_OR_NULL(dev->pm_domain))
 			ret = pm_genpd_add_subdomain(pd_to_genpd(dev->pm_domain), &scs[i]->pd);
+		else if (desc->pd_list)
+			ret = gdsc_add_subdomain_list(desc->pd_list, &scs[i]->pd);
+
 		if (ret)
 			return ret;
 	}
@@ -580,6 +613,8 @@ void gdsc_unregister(struct gdsc_desc *desc)
 			pm_genpd_remove_subdomain(scs[i]->parent, &scs[i]->pd);
 		else if (!IS_ERR_OR_NULL(dev->pm_domain))
 			pm_genpd_remove_subdomain(pd_to_genpd(dev->pm_domain), &scs[i]->pd);
+		else if (desc->pd_list)
+			gdsc_remove_subdomain_list(desc->pd_list, &scs[i]->pd);
 	}
 	of_genpd_del_provider(dev->of_node);
 }
diff --git a/drivers/clk/qcom/gdsc.h b/drivers/clk/qcom/gdsc.h
index 1e2779b823d1c8ca077c9b4cd0a0dbdf5f9457ef..dd843e86c05b2f30e6d9e978681580016333839d 100644
--- a/drivers/clk/qcom/gdsc.h
+++ b/drivers/clk/qcom/gdsc.h
@@ -80,6 +80,7 @@ struct gdsc_desc {
 	struct device *dev;
 	struct gdsc **scs;
 	size_t num;
+	struct dev_pm_domain_list *pd_list;
 };
 
 #ifdef CONFIG_QCOM_GDSC

-- 
2.45.2

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