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

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Date:   Thu, 1 Jun 2023 13:00:29 +0200
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     Tony Lindgren <tony@...mide.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>
Cc:     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 Tony,

On 25.05.2023 13:30, 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 manage serial controllers, let's set up a struct bus and 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.
>
> With the serial core port device we can now flush pending TX on the
> runtime PM resume as suggested by Johan.
>
> Suggested-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> Suggested-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Suggested-by: Jiri Slaby <jirislaby@...nel.org>
> Suggested-by: Johan Hovold <johan@...nel.org>
> Signed-off-by: Tony Lindgren <tony@...mide.com>

This patch landed in today's linux next-20230601 as commit 84a9582fd203 
("serial: core: Start managing serial controllers to enable runtime 
PM"). Unfortunately it breaks booting some of my test boards. This can 
be easily reproduced with QEMU and ARM64 virt machine. The last message 
I see in the log is:

[    3.084743] Run /sbin/init as init process

I've tried a hack posted here by Steven Price, but unfortunately it 
doesn't fix my issue. Reverting $subject on top of next-20230601 fixes 
the boot.

Here is my qemu test command (nothing really special...):

qemu-system-aarch64 -kernel Image -append "console=ttyAMA0 
no_console_suspend root=/dev/vda rootwait ip=::::target::off" -M virt 
-cpu cortex-a57 -smp 2 -m 1024 -device 
virtio-blk-device,drive=virtio-blk0 -device 
virtio-blk-device,drive=virtio-blk1 -drive 
file=qemu-virt-rootfs.raw,id=virtio-blk1,if=none,format=raw -drive 
file=initrd,id=virtio-blk0,if=none,format=raw -netdev user,id=user 
-device virtio-net-device,netdev=user -display none


 > ...

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland