linux-kernel - Re: [PATCH] omap3: give off mode enable a more prominent place

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Date:   Mon, 4 Feb 2019 19:33:11 +0100
From:   Andreas Kemnade <andreas@...nade.info>
To:     Tony Lindgren <tony@...mide.com>
Cc:     linux@...linux.org.uk, khilman@...nel.org,
        linux-omap@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, letux-kernel@...nphoenux.org
Subject: Re: [PATCH] omap3: give off mode enable a more prominent place

On Mon, 4 Feb 2019 07:56:04 -0800
Tony Lindgren <tony@...mide.com> wrote:

> * Andreas Kemnade <andreas@...nade.info> [190202 06:01]:
> > Enabling off mode was only reachable deeply hidden
> > in the debugfs. As powersaving is an important feature,
> > move the option out of its shady place.  
> 
> How about let's enable always if we have the twl4030
> configured to allow it? You can just check if the dts has
> "ti,twl4030-power-idle" or "ti,twl4030-power-idle-osc-off"
> properties set.
> 
> In order to enable deeper idle states, the user space still
> needs to idle the UARTs and possibly other hardware blocking
> idle. So we should be safe there.
> 
Let us not mix up runtime pm and system pm. The uarts need
to be idled for runtime suspend, but they are off/ret for
system suspend without userspace intervention, so allowing off mode
will have an influence even without uart runtime suspend,
and also probably for other powerdomains (non-core/per).
So we still need to be sure to handle at least some erratas and
context save/restore correctly.

Your Idea seems to be in pseudocode
if (powersaving_wanted)
	enable_off_mode()

I had something in mind like
if (system_is_trusted_to_handle_offmode()
	enable_off_mode()

Regards,
Andreas

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