linux-kernel - [RFC v2 3/6] drivers: boot_constraint: Add boot_constraints

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Date:   Wed, 12 Jul 2017 12:04:33 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jonathan Corbet <corbet@....net>
Cc:     Viresh Kumar <viresh.kumar@...aro.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Brown <broonie@...nel.org>,
        Stephen Boyd <sboyd@...eaurora.org>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        Shiraz Hashim <shashim@...eaurora.org>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-doc@...r.kernel.org
Subject: [RFC v2 3/6] drivers: boot_constraint: Add boot_constraints_disable kernel parameter

Users must be given an option to discard any constraints set by
bootloaders. For example, consider that a constraint is set for the LCD
controller's supply and the LCD driver isn't loaded by the kernel. If
the user doesn't need to use the LCD device, then he shouldn't be forced
to honour the constraint.

We can also think about finer control of such constraints with help of
some sysfs files, but a kernel parameter is fine to begin with.

Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
---
 Documentation/admin-guide/kernel-parameters.txt |  3 +++
 drivers/base/boot_constraint.c                  | 17 +++++++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 7737ab5d04b2..59ad24822d10 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -426,6 +426,9 @@
 			embedded devices based on command line input.
 			See Documentation/block/cmdline-partition.txt
 
+	boot_constraints_disable
+			Do not set any boot constraints for devices.
+
 	boot_delay=	Milliseconds to delay each printk during boot.
 			Values larger than 10 seconds (10000) are changed to
 			no delay (0).
diff --git a/drivers/base/boot_constraint.c b/drivers/base/boot_constraint.c
index 4e4332751c5f..d372ddfe1264 100644
--- a/drivers/base/boot_constraint.c
+++ b/drivers/base/boot_constraint.c
@@ -47,6 +47,17 @@ static DEFINE_MUTEX(constraint_devices_mutex);
 static int constraint_supply_add(struct constraint *constraint, void *data);
 static void constraint_supply_remove(struct constraint *constraint);
 
+static bool boot_constraints_disabled;
+
+static int __init constraints_disable(char *str)
+{
+	boot_constraints_disabled = true;
+	pr_debug("disabled\n");
+
+	return 0;
+}
+early_param("boot_constraints_disable", constraints_disable);
+
 
 /* Boot constraints core */
 
@@ -154,6 +165,9 @@ int boot_constraint_add(struct device *dev, enum boot_constraint_type type,
 	struct constraint *constraint;
 	int ret;
 
+	if (boot_constraints_disabled)
+		return -ENODEV;
+
 	mutex_lock(&constraint_devices_mutex);
 
 	/* Find or add the cdev type first */
@@ -211,6 +225,9 @@ void boot_constraints_remove(struct device *dev)
 	struct constraint_dev *cdev;
 	struct constraint *constraint, *temp;
 
+	if (boot_constraints_disabled)
+		return;
+
 	mutex_lock(&constraint_devices_mutex);
 
 	cdev = constraint_device_find(dev);
-- 
2.13.0.71.gd7076ec9c9cb