On 12/11/2014 04:59 PM, NeilBrown wrote:
> A "tty slave" is a device connected via UART.
> It may need a driver to, for example, power the device on
> when the tty is opened, and power it off when the tty
> is released.
>
> A "tty slave" is a platform device which is declared as a
> child of the uart in device-tree:
>
> &uart1 {
> bluetooth {
> compatible = "tty,regulator";
> vdd-supply = <&vaux4>;
> };
> };
>
> runtime power management is used to power-up the device
> on tty_open() and power-down on tty_release().
I have a couple of issues with this:
1) why does a child device imply power management and a platform
device? iow, what happens when someone else wants to have a
child device that does something different?
2) why is this tied to the tty core and not the serial core
if this is only for UART?
Regards,
Peter Hurley
> Signed-off-by: NeilBrown <neilb@xxxxxxx>
> ---
> .../devicetree/bindings/serial/of-serial.txt | 4 ++++
> drivers/tty/tty_io.c | 22 ++++++++++++++++++++
> 2 files changed, 26 insertions(+)
>
> diff --git a/Documentation/devicetree/bindings/serial/of-serial.txt b/Documentation/devicetree/bindings/serial/of-serial.txt
> index 8c4fd0332028..b59501ee2f21 100644
> --- a/Documentation/devicetree/bindings/serial/of-serial.txt
> +++ b/Documentation/devicetree/bindings/serial/of-serial.txt
> @@ -39,6 +39,10 @@ Optional properties:
> driver is allowed to detect support for the capability even without this
> property.
>
> +Optional child node:
> +- a platform device listed as a child node will be probed and
> + powered-on whenever the tty is in use (open).
> +
> Example:
>
> uart@80230000 {
> diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
> index 0508a1d8e4cd..7acdc6f093f4 100644
> --- a/drivers/tty/tty_io.c
> +++ b/drivers/tty/tty_io.c
> @@ -95,6 +95,8 @@
> #include <linux/seq_file.h>
> #include <linux/serial.h>
> #include <linux/ratelimit.h>
> +#include <linux/pm_runtime.h>
> +#include <linux/of_platform.h>
>
> #include <linux/uaccess.h>
>
> @@ -1683,6 +1685,17 @@ static int tty_release_checks(struct tty_struct *tty, struct tty_struct *o_tty,
> return 0;
> }
>
> +static int open_child(struct device *dev, void *data)
> +{
> + pm_runtime_get_sync(dev);
> + return 0;
> +}
> +static int release_child(struct device *dev, void *data)
> +{
> + pm_runtime_put_autosuspend(dev);
> + return 0;
> +}
> +
> /**
> * tty_release - vfs callback for close
> * @inode: inode of tty
> @@ -1712,6 +1725,8 @@ int tty_release(struct inode *inode, struct file *filp)
> long timeout = 0;
> int once = 1;
>
> + if (tty->dev)
> + device_for_each_child(tty->dev, NULL, release_child);
> if (tty_paranoia_check(tty, inode, __func__))
> return 0;
>
> @@ -2118,6 +2133,8 @@ retry_open:
> __proc_set_tty(current, tty);
> spin_unlock_irq(¤t->sighand->siglock);
> tty_unlock(tty);
> + if (tty->dev)
> + device_for_each_child(tty->dev, NULL, open_child);
> mutex_unlock(&tty_mutex);
> return 0;
> err_unlock:
> @@ -3207,6 +3224,11 @@ struct device *tty_register_device_attr(struct tty_driver *driver,
> retval = device_register(dev);
> if (retval)
> goto error;
> + if (device && device->of_node)
> + /* Children are platform devices and will be
> + * runtime_pm managed by this tty.
> + */
> + of_platform_populate(device->of_node, NULL, NULL, dev);
>
> return dev;
--
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