linux-kernel - Re: [PATCH v12 1/1] serial: core: Start managing serial controllers to enable runtime PM

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Message-ID: <20231003121455.GB34982@atomide.com>
Date:   Tue, 3 Oct 2023 15:14:55 +0300
From:   Tony Lindgren <tony@...mide.com>
To:     Maximilian Luz <luzmaximilian@...il.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Andy Shevchenko <andriy.shevchenko@...el.com>,
        Dhruva Gole <d-gole@...com>,
        Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
        John Ogness <john.ogness@...utronix.de>,
        Johan Hovold <johan@...nel.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Vignesh Raghavendra <vigneshr@...com>,
        linux-omap@...r.kernel.org,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org
Subject: Re: [PATCH v12 1/1] serial: core: Start managing serial controllers
 to enable runtime PM

Hi,

* Maximilian Luz <luzmaximilian@...il.com> [231003 11:57]:
> A bad workaround is to disable runtime PM, e.g. via
> 
>   echo on > /sys/bus/serial-base/devices/dw-apb-uart.4:0/dw-apb-uart.4:0.0/power/control

If the touchscreen controller driver(s) are using serdev they are
children of the dw-apb-uart.4:0.0 and can use runtime PM calls to
block the parent device from idling as necessary. The hierarchy
unless changed using ignore_children.

Then when the children are done, seem like dw-apb-uart driver should
use force_suspend and force_resume calls in the system suspend path.

Do you have some mainline kernel test case available or is this
still out of tree code?

Regards,

Tony