linux-kernel - Re: [PATCH v14 05/10] power: reset: reboot-mode: Expose sysfs for registered reboot

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Message-ID: <lgoahuqgoajuj352h7rnjfyeeyf24x45pj3qmidc6qqrc75vej@3hrblxle7uyk>
Date: Tue, 16 Sep 2025 21:02:41 +0200
From: Sebastian Reichel <sebastian.reichel@...labora.com>
To: Shivendra Pratap <shivendra.pratap@....qualcomm.com>
Cc: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>, 
	Bjorn Andersson <andersson@...nel.org>, Rob Herring <robh@...nel.org>, 
	Sudeep Holla <sudeep.holla@....com>, Souvik Chakravarty <Souvik.Chakravarty@....com>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Andy Yan <andy.yan@...k-chips.com>, Mark Rutland <mark.rutland@....com>, 
	Lorenzo Pieralisi <lpieralisi@...nel.org>, Arnd Bergmann <arnd@...db.de>, 
	Konrad Dybcio <konradybcio@...nel.org>, cros-qcom-dts-watchers@...omium.org, 
	Vinod Koul <vkoul@...nel.org>, Catalin Marinas <catalin.marinas@....com>, 
	Will Deacon <will@...nel.org>, Florian Fainelli <florian.fainelli@...adcom.com>, 
	Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>, Mukesh Ojha <mukesh.ojha@....qualcomm.com>, 
	Stephen Boyd <swboyd@...omium.org>, Andre Draszik <andre.draszik@...aro.org>, 
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org, devicetree@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, linux-arm-msm@...r.kernel.org, 
	Elliot Berman <quic_eberman@...cinc.com>, Srinivas Kandagatla <srini@...nel.org>
Subject: Re: [PATCH v14 05/10] power: reset: reboot-mode: Expose sysfs for
 registered reboot_modes

Hi,

On Fri, Aug 15, 2025 at 08:05:10PM +0530, Shivendra Pratap wrote:
> Currently, there is no standardized mechanism for userspace to
> discover which reboot-modes are supported on a given platform.
> This limitation forces tools and scripts to rely on hardcoded
> assumptions about the supported reboot-modes.
> 
> Create a class 'reboot-mode' and a device under it to expose a
> sysfs interface to show the available reboot mode arguments to
> userspace.
> 
> Provision the register function with an additional parameter to
> get an explicit driver_name. Create the device using this
> driver_name. For platform drivers, use the driver_name configured
> in dev node.
> 
> This results in the creation of:
>   /sys/class/reboot-mode/<driver>/reboot_modes
> 
> This read-only sysfs file will exposes the list of supported
> reboot modes arguments provided by the driver, enabling userspace
> to query the list of arguments.
> 
> Align the clean up path to maintain backward compatibility for
> existing reboot-mode based drivers.
> 
> Signed-off-by: Shivendra Pratap <shivendra.pratap@....qualcomm.com>
> ---
>  drivers/power/reset/reboot-mode.c | 131 +++++++++++++++++++++++++++++++-------
>  include/linux/reboot-mode.h       |   4 +-
>  2 files changed, 110 insertions(+), 25 deletions(-)
> 
> diff --git a/drivers/power/reset/reboot-mode.c b/drivers/power/reset/reboot-mode.c
> index ac81b8b0a9b7fc31f8ef21024333a050087ce90f..7ecab050e496af3e1cc01c1a4614787707cb74b4 100644
> --- a/drivers/power/reset/reboot-mode.c
> +++ b/drivers/power/reset/reboot-mode.c
> @@ -6,6 +6,7 @@
>  #define pr_fmt(fmt)	"reboot-mode: " fmt
>  
>  #include <linux/device.h>
> +#include <linux/err.h>
>  #include <linux/init.h>
>  #include <linux/kernel.h>
>  #include <linux/list.h>
> @@ -23,6 +24,8 @@ struct mode_info {
>  	struct list_head list;
>  };
>  
> +static struct class *rb_class;
> +
>  static u64 get_reboot_mode_magic(struct reboot_mode_driver *reboot, const char *cmd)
>  {
>  	const char *normal = "normal";
> @@ -75,26 +78,121 @@ static int reboot_mode_notify(struct notifier_block *this,
>  	return NOTIFY_DONE;
>  }
>  
> +static void release_reboot_mode_device(struct device *dev, void *res);
> +
> +static ssize_t reboot_modes_show(struct device *dev, struct device_attribute *attr, char *buf)
> +{
> +	struct reboot_mode_driver **devres_reboot;
> +	struct reboot_mode_driver *reboot;
> +	struct mode_info *info;
> +	ssize_t size = 0;
> +
> +	devres_reboot = devres_find(dev, release_reboot_mode_device, NULL, NULL);
> +	if (!devres_reboot || !(*devres_reboot))
> +		return -ENODATA;
> +
> +	reboot = *devres_reboot;
> +	mutex_lock(&reboot->rb_lock);
> +	list_for_each_entry(info, &reboot->head, list) {
> +		size += sprintf(buf + size, "%s ", info->mode);

sysfs_emit_at

> +	}
> +	mutex_unlock(&reboot->rb_lock);
> +
> +	if (size) {
> +		size += sprintf(buf + size - 1, "\n");

sysfs_emit_at

> +		return size;
> +	}
> +
> +	return -ENODATA;
> +}
> +static DEVICE_ATTR_RO(reboot_modes);
> +
> +static void release_reboot_mode_device(struct device *dev, void *res)
> +{
> +	struct reboot_mode_driver *reboot = *(struct reboot_mode_driver **)res;
> +	struct mode_info *info;
> +	struct mode_info *next;
> +
> +	unregister_reboot_notifier(&reboot->reboot_notifier);
> +
> +	mutex_lock(&reboot->rb_lock);
> +	list_for_each_entry_safe(info, next, &reboot->head, list) {
> +		list_del(&info->list);
> +		kfree_const(info->mode);
> +		kfree(info);
> +	}
> +	mutex_unlock(&reboot->rb_lock);
> +
> +	device_remove_file(reboot->reboot_dev, &dev_attr_reboot_modes);
> +}
> +
> +static int create_reboot_mode_device(struct reboot_mode_driver *reboot,
> +				     const char *dev_name)

Instead of adding more and more arguments to this, just add a name
field to struct reboot_mode_driver.

Greetings,

-- Sebastian

> [...]

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