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

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Date:	Tue, 09 Apr 2013 12:07:05 -0700
From:	Kevin Hilman <khilman@...aro.org>
To:	Sourav Poddar <sourav.poddar@...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"

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.

>     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.

Thanks,

Kevin
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