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 14:26:17 -0700
From:	Kevin Hilman <khilman@...aro.org>
To:	"Bedia\, Vaibhav" <vaibhav.bedia@...com>
Cc:	"Poddar\, Sourav" <sourav.poddar@...com>,
	"gregkh\@linuxfoundation.org" <gregkh@...uxfoundation.org>,
	"tony\@atomide.com" <tony@...mide.com>,
	"rmk+kernel\@arm.linux.org.uk" <rmk+kernel@....linux.org.uk>,
	"linux-omap\@vger.kernel.org" <linux-omap@...r.kernel.org>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-serial\@vger.kernel.org" <linux-serial@...r.kernel.org>,
	"Shilimkar\, Santosh" <santosh.shilimkar@...com>,
	"Balbi\, Felipe" <balbi@...com>, "Nayak\, Rajendra" <rnayak@...com>
Subject: Re: [PATCHv3] driver: serial: prevent UART console idle on suspend while using "no_console_suspend"

"Bedia, Vaibhav" <vaibhav.bedia@...com> writes:

> Hi Sourav,
>
> On Wed, Apr 10, 2013 at 15:13:44, Poddar, Sourav wrote:
> [...]
>> Yes, had a look at that and found your situation similar to UART.
>> 
>> But how exactly this gets used, I mean I don't  see any drivers/ in mainline
>> making use of this compatible string  "ti,am3352-ocmcram".  ?
>
> OCMC clock is enabled during bootup (not sure whether that's the h/w
> default or ROM does it) since the initial bootloader runs from there.
> By marking the corresponding hwmod with HWMOD_INIT_NO_IDLE we leave the
> clock running. Right now the sram code under arch/arm/plat-omap/ is what
> manages the OCMC. I guess this needs to move somewhere under drivers/
> and start managing the clocks. Even then we'll need a mechanism
> to leave the clocks running as part of the kernel suspend process
> since the assembly code which runs at the fag end of the suspend
> process runs out of OCMC and hence we can't cut its clock.
>
> On AM335x, the OCMC clock is cut to have PER power domain transition
> but that's done in the WKUP-M3 firmware when going down. During the
> wakeup sequence, WKUP-M3 re-enables the OCMC clock so that when the
> kernel resumes the h/w state is same.

OK, but *today*, in *mainline*, where in the linux kernel (not the M3
firmware) is the OCMRAM clock cut during suspend?

>From what I can see, there is no driver for this device, so there are no
system PM calls being done for that device, and thus no omap_device
calls being done for that device, so the no_idle_on_suspend has no
effect.

Kevin
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