linux-kernel - [RFC PATCH] PM / OPP: Don't support OPP if it provides supported-hw but platform does not

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Message-ID: <20160923200747.3948-1-d-gerlach@ti.com>
Date:   Fri, 23 Sep 2016 15:07:47 -0500
From:   Dave Gerlach <d-gerlach@...com>
To:     <linux-kernel@...r.kernel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>
CC:     <linux-pm@...r.kernel.org>, Nishanth Menon <nm@...com>,
        Lee Jones <lee.jones@...aro.org>,
        Dave Gerlach <d-gerlach@...com>
Subject: [RFC PATCH] PM / OPP: Don't support OPP if it provides supported-hw but platform does not

The OPP framework allows each OPP to set a opp-supported-hw property
which provides values that are matched against supported_hw values
provided by the platform to limit support for certain OPPs on specific
hardware. Currently, if the platform does not set supported_hw values,
all OPPs are interpreted as supported, even if they have provided their
own opp-supported-hw values.

If an OPP has provided opp-supported-hw, it is indicating that there is
some specific hardware configuration it is supported by. These constraints
should be honored, and if no supported_hw has been provided by the
platform, there is no way to determine if that OPP is actually supported,
so it should be marked as not supported.

Signed-off-by: Dave Gerlach <d-gerlach@...com>
---
 drivers/base/power/opp/of.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/drivers/base/power/opp/of.c b/drivers/base/power/opp/of.c
index 1dfd3dd92624..ccccaf9f8968 100644
--- a/drivers/base/power/opp/of.c
+++ b/drivers/base/power/opp/of.c
@@ -71,8 +71,18 @@ static bool _opp_is_supported(struct device *dev, struct opp_table *opp_table,
 	u32 version;
 	int ret;

-	if (!opp_table->supported_hw)
-		return true;
+	if (!opp_table->supported_hw) {
+		/*
+		 * In the case that no supported_hw has been set by the
+		 * platform but there is an opp-supported-hw value set for
+		 * an OPP then the OPP should not be enabled as there is
+		 * no way to see if the hardware supports it.
+		 */
+		if (of_find_property(np, "opp-supported-hw", NULL))
+			return false;
+		else
+			return true;
+	}

 	while (count--) {
 		ret = of_property_read_u32_index(np, "opp-supported-hw", count,
-- 
2.9.3