linux-kernel - Re: [PATCH 1/2] serdev: add controller runtime PM support

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Date:   Fri, 11 May 2018 14:35:53 +0200
From:   Sebastian Reichel <sre@...nel.org>
To:     Johan Hovold <johan@...nel.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rob Herring <robh@...nel.org>,
        Tony Lindgren <tony@...mide.com>,
        "H. Nikolaus Schaller" <hns@...delico.com>,
        Andreas Kemnade <andreas@...nade.info>,
        Mark Rutland <mark.rutland@....com>,
        Arnd Bergmann <arnd@...db.de>, Pavel Machek <pavel@....cz>,
        linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org,
        linux-pm@...r.kernel.org
Subject: Re: [PATCH 1/2] serdev: add controller runtime PM support

Hi Johan,

On Wed, May 09, 2018 at 11:44:18AM +0200, Johan Hovold wrote:
> Add support for controller runtime power management to serdev core. This
> is needed to allow slave drivers to manage the runtime PM state of the
> underlying serial controller when its driver, in turn, implements more
> aggressive runtime power management (e.g. using autosuspend).
> 
> For some applications, for example, where loss off initial data after a
> remote-wakeup event is acceptable or where rx is not used at all,
> aggressive serial controller runtime PM may be used without further
> involvement of the slave driver. But when this is not the case, the
> slave driver must be able to indicate when incoming data is expected in
> order to avoid data loss.
> 
> To facilitate the common case, where the serial controller power state
> is active whenever the port is open (which is the case with just about
> every serial driver), and where data loss is not acceptable and cannot
> even be prevented by explicit controller runtime power management, an
> RPM reference is taken in serdev open and put again at close. This
> reference can later be balanced by any serdev driver which wants and/or
> can handle aggressive controller runtime PM.
> 
> Note that the .ignore_children flag is set for the serdev controller to
> allow the underlying hardware to idle when no I/O is expected, regardless
> of the slave device RPM state.
> 
> Signed-off-by: Johan Hovold <johan@...nel.org>
> ---

Looks good to me.

Reviewed-by: Sebastian Reichel <sebastian.reichel@...labora.co.uk>

-- Sebastian

>  drivers/tty/serdev/core.c | 33 ++++++++++++++++++++++++++++++---
>  1 file changed, 30 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/tty/serdev/core.c b/drivers/tty/serdev/core.c
> index df93b727e984..e5e84303faca 100644
> --- a/drivers/tty/serdev/core.c
> +++ b/drivers/tty/serdev/core.c
> @@ -13,6 +13,7 @@
>  #include <linux/module.h>
>  #include <linux/of.h>
>  #include <linux/of_device.h>
> +#include <linux/pm_runtime.h>
>  #include <linux/serdev.h>
>  #include <linux/slab.h>
>  
> @@ -143,11 +144,28 @@ EXPORT_SYMBOL_GPL(serdev_device_remove);
>  int serdev_device_open(struct serdev_device *serdev)
>  {
>  	struct serdev_controller *ctrl = serdev->ctrl;
> +	int ret;
>  
>  	if (!ctrl || !ctrl->ops->open)
>  		return -EINVAL;
>  
> -	return ctrl->ops->open(ctrl);
> +	ret = ctrl->ops->open(ctrl);
> +	if (ret)
> +		return ret;
> +
> +	ret = pm_runtime_get_sync(&ctrl->dev);
> +	if (ret < 0) {
> +		pm_runtime_put_noidle(&ctrl->dev);
> +		goto err_close;
> +	}
> +
> +	return 0;
> +
> +err_close:
> +	if (ctrl->ops->close)
> +		ctrl->ops->close(ctrl);
> +
> +	return ret;
>  }
>  EXPORT_SYMBOL_GPL(serdev_device_open);
>  
> @@ -158,6 +176,8 @@ void serdev_device_close(struct serdev_device *serdev)
>  	if (!ctrl || !ctrl->ops->close)
>  		return;
>  
> +	pm_runtime_put(&ctrl->dev);
> +
>  	ctrl->ops->close(ctrl);
>  }
>  EXPORT_SYMBOL_GPL(serdev_device_close);
> @@ -416,6 +436,9 @@ struct serdev_controller *serdev_controller_alloc(struct device *parent,
>  
>  	dev_set_name(&ctrl->dev, "serial%d", id);
>  
> +	pm_runtime_no_callbacks(&ctrl->dev);
> +	pm_suspend_ignore_children(&ctrl->dev, true);
> +
>  	dev_dbg(&ctrl->dev, "allocated controller 0x%p id %d\n", ctrl, id);
>  	return ctrl;
>  
> @@ -547,20 +570,23 @@ int serdev_controller_add(struct serdev_controller *ctrl)
>  	if (ret)
>  		return ret;
>  
> +	pm_runtime_enable(&ctrl->dev);
> +
>  	ret_of = of_serdev_register_devices(ctrl);
>  	ret_acpi = acpi_serdev_register_devices(ctrl);
>  	if (ret_of && ret_acpi) {
>  		dev_dbg(&ctrl->dev, "no devices registered: of:%d acpi:%d\n",
>  			ret_of, ret_acpi);
>  		ret = -ENODEV;
> -		goto out_dev_del;
> +		goto err_rpm_disable;
>  	}
>  
>  	dev_dbg(&ctrl->dev, "serdev%d registered: dev:%p\n",
>  		ctrl->nr, &ctrl->dev);
>  	return 0;
>  
> -out_dev_del:
> +err_rpm_disable:
> +	pm_runtime_disable(&ctrl->dev);
>  	device_del(&ctrl->dev);
>  	return ret;
>  };
> @@ -591,6 +617,7 @@ void serdev_controller_remove(struct serdev_controller *ctrl)
>  
>  	dummy = device_for_each_child(&ctrl->dev, NULL,
>  				      serdev_remove_device);
> +	pm_runtime_disable(&ctrl->dev);
>  	device_del(&ctrl->dev);
>  }
>  EXPORT_SYMBOL_GPL(serdev_controller_remove);
> -- 
> 2.17.0
> 

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