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

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Date:	Tue, 23 Apr 2013 10:44:35 +0530
From:	Sourav Poddar <sourav.poddar@...com>
To:	Kevin Hilman <khilman@...aro.org>
CC:	Grygorii Strashko <grygorii.strashko@...com>,
	<gregkh@...uxfoundation.org>, <tony@...mide.com>,
	<rmk+kernel@....linux.org.uk>, <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"

Hi Kevin,
On Tuesday 23 April 2013 12:06 AM, Kevin Hilman wrote:
> Grygorii Strashko<grygorii.strashko@...com>  writes:
>
>> 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.
> Correct.
>
> Sourav, as I mentioned when I suggested this approach, it should be done
> *only* during suspend.
>
Yes, got the point.
>> 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.
> So set an 'is_suspending' flag in ->suspend (it may need to be in
> ->prepare) and clear it in ->resume (->complete), and check the flag in
> the ->runtime_supend() callback.  It's not uncommon for drivers to have
> such a flag for various reasons.
>
Ok. Will adapt the next version inline with the above suggestions.
>> 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.
> No, we need to get rid of ti,no_idle_on_suspend.  It's an ugly,
> OMAP-specific hack (and I'm free to insult it because I introduced it.)
>
> Kevin
>

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