linux-kernel - Re: [PATCH] i2c: designware: separate ops for system_sleep_pm and runtime

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Message-ID: <20150518082823.GH1490@lahna.fi.intel.com>
Date:	Mon, 18 May 2015 11:28:23 +0300
From:	Mika Westerberg <mika.westerberg@...ux.intel.com>
To:	Jisheng Zhang <jszhang@...vell.com>
Cc:	wsa@...-dreams.de, linux-i2c@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] i2c: designware: separate ops for system_sleep_pm and
 runtime_pm

On Fri, May 15, 2015 at 08:31:39PM +0800, Jisheng Zhang wrote:
> Commit 1fc2fe204cb9 ("i2c: designware: Add runtime PM hooks") adds
> runtime pm support using the same ops for system sleep and runtime pm.
> When suspend to ram, the i2c host may have been runtime suspended, thus
> i2c_dw_disable() hangs.

It hangs because it has already been powered off, right?

> This patch fixes this issue by separating ops for system sleep pm and
> runtime pm, and in the system suspend/resume path, runtime pm apis are
> used to ensure the device is at correct state.

I can see that this fixes the issue with the platform driver (as the
platform bus core doesn't power on the device automatically as opposed
to other buses, like PCI). However, I'm thinking that can we do better
here.

Instead of powering the device on again, can't we leave it in low power
state? Recently added 'dev->power.direct_complete' may be used to
achieve that, I think.
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