linux-kernel - Re: [PATCH v5 1/1] serial: core: Start managing serial controllers to enable runtime PM

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Message-ID: <Y9oI8m132aQOeSed@atomide.com>
Date:   Wed, 1 Feb 2023 08:38:42 +0200
From:   Tony Lindgren <tony@...mide.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Jiri Slaby <jirislaby@...nel.org>,
        Andy Shevchenko <andriy.shevchenko@...el.com>,
        Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
        Johan Hovold <johan@...nel.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Vignesh Raghavendra <vigneshr@...com>,
        linux-omap@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-serial@...r.kernel.org
Subject: Re: [PATCH v5 1/1] serial: core: Start managing serial controllers
 to enable runtime PM

* Greg Kroah-Hartman <gregkh@...uxfoundation.org> [230131 10:10]:
> On Mon, Jan 16, 2023 at 09:59:58AM +0200, Tony Lindgren wrote:
> > We want to enable runtime PM for serial port device drivers in a generic
> > way. To do this, we want to have the serial core layer manage the
> > registered physical serial controller devices.
> > 
> > To do this, let's set up a struct device for the serial core controller
> > as suggested by Greg and Jiri. The serial core controller devices are
> > children of the physical serial port device. The serial core controller
> > device is needed to support multiple different kind of ports connected
> > to single physical serial port device.
> > 
> > Let's also set up a struct device for the serial core port. The serial
> > core port instances are children of the serial core controller device.
> 
> Looking better, but why is this new device a platform device?  That
> feels odd, you should never have a platform device hanging off of a
> non-platform device, right?

No special need for it to be a platform device. It just is easy to set
up, and for my test case the serial port physical device is also a
platform device.

What's your preference here?

> What does the sysfs tree look like now with this patch applied?

Below are two examples of what's in sysfs.

Regards,

Tony

8< -----------------
On arm64 with two physical 8250 devices I have:

# ls -l /sys/devices/platform/serial8250/
total 0
lrwxrwxrwx    1 root     root             0 Jan  1  1970 driver -> ../../../bus/platform/drivers/serial8250
-rw-r--r--    1 root     root          4096 Jan  1  1970 driver_override
-r--r--r--    1 root     root          4096 Jan  1  1970 modalias
drwxr-xr-x    2 root     root             0 Jan  1  1970 power
drwxr-xr-x    5 root     root             0 Jan  1  1970 serial-ctrl.0.auto
lrwxrwxrwx    1 root     root             0 Jan  1  1970 subsystem -> ../../../bus/platform
drwxr-xr-x    4 root     root             0 Jan  1  1970 tty
-rw-r--r--    1 root     root          4096 Jan  1  1970 uevent

# ls -l /sys/devices/platform/serial8250/serial-ctrl*
total 0
lrwxrwxrwx    1 root     root             0 Jan  1  1970 driver -> ../../../../bus/platform/drivers/serial-ctrl
-rw-r--r--    1 root     root          4096 Jan  1  1970 driver_override
-r--r--r--    1 root     root          4096 Jan  1  1970 modalias
drwxr-xr-x    2 root     root             0 Jan  1  1970 power
drwxr-xr-x    3 root     root             0 Jan  1  1970 serial-port.1.auto
drwxr-xr-x    3 root     root             0 Jan  1  1970 serial-port.4.auto
lrwxrwxrwx    1 root     root             0 Jan  1  1970 subsystem -> ../../../../bus/platform
-rw-r--r--    1 root     root          4096 Jan  1  1970 uevent

On x86_64 qemu with one port I have:

# ls -l /sys/devices/pnp0/00:04/
total 0
lrwxrwxrwx    1 root     root             0 Feb  1 06:13 driver -> ../../../bus/pnp/drivers/serial
lrwxrwxrwx    1 root     root             0 Feb  1 06:13 firmware_node -> ../../LNXSYSTM:00/LNXSYBUS:00/PNP0A03:00/device:01/PNP0501:00
-r--r--r--    1 root     root          4096 Feb  1 06:13 id
-r--r--r--    1 root     root          4096 Feb  1 06:13 options
-rw-r--r--    1 root     root          4096 Feb  1 06:13 resources
drwxr-xr-x    3 root     root             0 Feb  1 06:12 serial-ctrl.0.auto
lrwxrwxrwx    1 root     root             0 Feb  1 06:13 subsystem -> ../../../bus/pnp
drwxr-xr-x    3 root     root             0 Feb  1 06:12 tty
-rw-r--r--    1 root     root          4096 Feb  1 06:12 uevent

# ls -l /sys/devices/pnp0/00:04/serial-ctrl.0.auto/
total 0
lrwxrwxrwx    1 root     root             0 Feb  1 06:13 driver -> ../../../../bus/platform/drivers/serial-ctrl
-rw-r--r--    1 root     root          4096 Feb  1 06:13 driver_override
-r--r--r--    1 root     root          4096 Feb  1 06:13 modalias
drwxr-xr-x    2 root     root             0 Feb  1 06:12 serial-port.1.auto
lrwxrwxrwx    1 root     root             0 Feb  1 06:13 subsystem -> ../../../../bus/platform
-rw-r--r--    1 root     root          4096 Feb  1 06:12 uevent