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[RFC 3/5] drivers: boot_constraint: Add boot_constraints_disable kernel parameter

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  [RFC 3/5] drivers: boot_constraint: Add boot_constraints_disable kernel parameter Viresh Kumar <viresh.kumar@linaro.org> - 2017-06-28 12:30 +0200
    Re: [RFC 3/5] drivers: boot_constraint: Add boot_constraints_disable  kernel parameter Randy Dunlap <rdunlap@infradead.org> - 2017-06-28 18:00 +0200

#1676533 — [RFC 3/5] 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@linaro.org>
---
 Documentation/admin-guide/kernel-parameters.txt |  2 ++
 drivers/base/boot_constraint.c                  | 17 +++++++++++++++++
 2 files changed, 19 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 7737ab5d04b2..35e8a298bfc1 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -426,6 +426,8 @@
 			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 495344e6405b..ab766d60191a 100644
--- a/drivers/base/boot_constraint.c
+++ b/drivers/base/boot_constraint.c
@@ -45,6 +45,17 @@ 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 constraints_disabled;
+
+static int __init constraints_disable(char *str)
+{
+	constraints_disabled = true;
+	pr_debug("disabled\n");
+
+	return 0;
+}
+early_param("boot_constraints_disable", constraints_disable);
+
 
 /* Boot constraints core */
 
@@ -152,6 +163,9 @@ int boot_constraint_add(struct device *dev, enum boot_constraint_type type,
 	struct constraint *constraint;
 	int ret;
 
+	if (constraints_disabled)
+		return -ENODEV;
+
 	mutex_lock(&constraint_devices_mutex);
 
 	/* Find or add the cdev type first */
@@ -202,6 +216,9 @@ void boot_constraints_remove(struct device *dev)
 	struct constraint_dev *cdev;
 	struct constraint *constraint, *temp;
 
+	if (constraints_disabled)
+		return;
+
 	mutex_lock(&constraint_devices_mutex);
 
 	cdev = constraint_device_find(dev);
-- 
2.13.0.71.gd7076ec9c9cb

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#1676877 — Re: [RFC 3/5] drivers: boot_constraint: Add boot_constraints_disable kernel parameter

On 06/28/2017 03:26 AM, Viresh Kumar wrote:
> 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@linaro.org>
> ---
>  Documentation/admin-guide/kernel-parameters.txt |  2 ++
>  drivers/base/boot_constraint.c                  | 17 +++++++++++++++++
>  2 files changed, 19 insertions(+)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 7737ab5d04b2..35e8a298bfc1 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -426,6 +426,8 @@
>  			embedded devices based on command line input.
>  			See Documentation/block/cmdline-partition.txt
>  
> +	boot_constraints_disable = Do not set any boot constraints for devices.
> +

No '=' sign.  That is only used when there is a following parameter value.


>  	boot_delay=	Milliseconds to delay each printk during boot.
>  			Values larger than 10 seconds (10000) are changed to
>  			no delay (0).


-- 
~Randy

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