linux-kernel - Re: [PATCHv2 2/5] driver: serial: omap: prevent runtime PM for "no_console

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Date:	Mon, 22 Apr 2013 17:48:55 +0300
From:	Grygorii Strashko <grygorii.strashko@...com>
To:	Sourav Poddar <sourav.poddar@...com>
CC:	<gregkh@...uxfoundation.org>, <tony@...mide.com>,
	<rmk+kernel@....linux.org.uk>, <khilman@...aro.org>,
	<linux-serial@...r.kernel.org>, <linux-omap@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCHv2 2/5] driver: serial: omap: prevent runtime PM for "no_console_suspend"

On 04/22/2013 04:43 PM, Sourav Poddar wrote:
> The driver manages "no_console_suspend" by preventing runtime PM
> during the suspend path, which forces the console UART to stay awake.
>
> Signed-off-by: Sourav Poddar <sourav.poddar@...com>
> ---
>   drivers/tty/serial/omap-serial.c |    5 ++++-
>   1 files changed, 4 insertions(+), 1 deletions(-)
>
> diff --git a/drivers/tty/serial/omap-serial.c b/drivers/tty/serial/omap-serial.c
> index 08332f3..640b14e 100644
> --- a/drivers/tty/serial/omap-serial.c
> +++ b/drivers/tty/serial/omap-serial.c
> @@ -1582,7 +1582,7 @@ static int serial_omap_runtime_suspend(struct device *dev)
>   	struct uart_omap_port *up = dev_get_drvdata(dev);
>   	struct omap_uart_port_info *pdata = dev->platform_data;
>   
> -	if (!up)
> +	if (!up || (!console_suspend_enabled && uart_console(&up->port)))
>   		return -EINVAL;
Hi Sourav,
No ) You will block Runtime PM for console UART forever, but instead
it need to be blocked only during suspend - autosuspend should continue 
working.
But this will be not easy, again, -
because System suspend isn't synchronized with Runtime PM (I mean,
serial_omap_suspend/resume() may be called from one thread and
serial_omap_runtime_suspend/resume() from another at same time).
And now, serial_omap_suspend() callback is the only one place where you
can detect that system is going to sleep.

Personally, i don't believe in such approach (my experiences from K3.4 
said me
that there will be more problems than benefits).

And, I like combination of "no_console_suspend" in bootargs +
"ti,no_idle_on_suspend" for console UART in DT, because 1) it's debug 
option and 2) until
smth. will be decided about OMAP OCP Bus it can be used.

It's just my opinion.

Regards,
-grygorii
>   
>   	if (!pdata)
> @@ -1614,6 +1614,9 @@ static int serial_omap_runtime_resume(struct device *dev)
>   
>   	int loss_cnt = serial_omap_get_context_loss_count(up);
>   
> +	if (!console_suspend_enabled && uart_console(&up->port))
> +		return -EINVAL;
> +
>   	if (loss_cnt < 0) {
>   		dev_err(dev, "serial_omap_get_context_loss_count failed : %d\n",
>   			loss_cnt);

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