linux-kernel - Re: [PATCHv3] driver: serial: prevent UART console idle on suspend while using "no_console

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Date:	Wed, 10 Apr 2013 11:37:28 +0530
From:	Sourav Poddar <sourav.poddar@...com>
To:	Kevin Hilman <khilman@...aro.org>, <vaibhav.bedia@...com>
CC:	<gregkh@...uxfoundation.org>, <tony@...mide.com>,
	<rmk+kernel@....linux.org.uk>, <linux-omap@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <linux-serial@...r.kernel.org>,
	Santosh Shilimkar <santosh.shilimkar@...com>,
	Felipe Balbi <balbi@...com>, Rajendra nayak <rnayak@...com>
Subject: Re: [PATCHv3] driver: serial: prevent UART console idle on suspend
 while using "no_console_suspend"

Hi,
On Wednesday 10 April 2013 12:37 AM, Kevin Hilman wrote:
> Sourav Poddar<sourav.poddar@...com>  writes:
>
>> Hi Kevin,
>> On Friday 05 April 2013 11:10 PM, Kevin Hilman wrote:
>>> Sourav Poddar<sourav.poddar@...com>   writes:
>>>
>>>> With dt boot, uart wakeup after suspend is non functional while using
>>>> "no_console_suspend" in the bootargs. With "no_console_suspend" used, we
>>>> should prevent the runtime suspend of the uart port which is getting used
>>>> as an console.
>>>>
>>>> Cc: Santosh Shilimkar<santosh.shilimkar@...com>
>>>> Cc: Felipe Balbi<balbi@...com>
>>>> Cc: Rajendra nayak<rnayak@...com>
>>>> Tested on omap5430evm, omap4430sdp.
>>>>
>>>> Signed-off-by: Sourav Poddar<sourav.poddar@...com>
>>> Rather than make these special checks inside the driver's runtime PM
>>> callbacks, you should just disable runtime PM (pm_runtime_disable())
>>>
>>> Then, this should be broken into 2 patches.
>>>
>>> 1) serial core: add the '->is_console' flag.  (nit on naming: don't call
>>>      it port_is_console, since the struct is already a uart_port)
>>>
>>> 2) In the OMAP UART driver's ->prepare callback, check the is_console flag
>>>      and pm_runtime_disable() accordingly  (then pm_runtime_enable() in
>>>      the drivers's ->complete callback.
>>>
>>> Kevin
>> I was working on your above suggestions, but realised there is not
>> only console
>> uart which has the requirement of keeping the clocks enabled while going on
>> suspend.
>>
>> If you see arch/arm/boot/dts/am33xx.dtsi, there is a ocmcram which has
>> "no_idle_on_suspend" property used.
> Can you please ask the AM33xx folks how (and why) this is being used?
>
> I don't see/find a driver for this device in mainline, so without a
> driver this flag will not be used.
>
Looping in Vaibhav Bedia for ocmcram..

[Vaibhav]:
   There is a discussion going on about a cleaner way of handling
   ti, no_idle_on_suspend" part (as this is a sort of hack). We got a way
   around for UART ($subject) by making serial core/driver handle this 
for us.
   But with this, we will delete codes around "no_idle_on_suspend" flag in
   omap_device file.

   But, we realised that its not only UART which requires the clocks to 
be active
   whie going for suspend. There is a dts entry for ocmcram also.

   As Kevin also pointed out, we don't see a driver for this device in 
mainline, It would be
   great if you can explain how its getting used?

   You can find the complete discussion on v3 here:
      https://lkml.org/lkml/2013/4/5/239

>>      ocmcram: ocmcram@...00000 {
>>                          compatible = "ti,am3352-ocmcram";
>>                          reg =<0x40300000 0x10000>;
>>                          ti,hwmods = "ocmcram";
>>                          ti,no_idle_on_suspend;
>>          };
>> This property gets checked in omap_device file and correspondingly
>> od->flags is set.
>>
>> Based on your above inputs, the patches which I cooked up is
>> inlined[1]. Though, the below
>> patches works fine for uart case. The patches will effect ocmcram case
>> and I am inling them
>> "just for discussion".
> Could you also have a look at Russell's suggestion for getting rid of
> the 'is_console' flag.
>
[Kevin]: Yes, will do that.
> Thanks,
>
> Kevin
~Sourav
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