From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kevin Hilman Subject: Re: [linux-pm] [PATCH] i2c: OMAP: fix static suspend vs. runtime suspend Date: Mon, 31 Jan 2011 08:09:12 -0800 Message-ID: <877hdl9hsn.fsf@ti.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: In-Reply-To: (Alan Stern's message of "Mon, 31 Jan 2011 10:13:13 -0500 (EST)") Sender: linux-omap-owner@vger.kernel.org To: Alan Stern Cc: Rajendra Nayak , Ben Dooks , linux-i2c@vger.kernel.org, linux-pm@lists.linux-foundation.org, linux-omap@vger.kernel.org, linux-arm-kernel@lists.infradead.org List-Id: linux-i2c@vger.kernel.org Alan Stern writes: > On Mon, 31 Jan 2011, Rajendra Nayak wrote: > >> Can you elaborate a bit more on how/why runtime PM transitions >> are disabled during system suspend, and how is it taken care >> of that a runtime resume of a device works however a subsequent >> runtime (re)suspend does not? > > I'll answer for Kevin. This is done by the PM core, in order to > prevent runtime power transitions from interfering with a system power > transition. The PM core increments the device's usage_count; this > prevents the device from being runtime-suspended but it allows > runtime-resume calls to go through. I understand how this works, but frankly I'm still a bit fuzzy on why. I guess I'm still missing a good understanding of what "interfering with a system power transition" means, and why a runtime suspend qualifies as interfering but not a runtime resume. More specifically, the reason for $SUBJECT patch is precisely because a runtime resume is allowed, a runtime suspend is not, and thus a system power transititon is prevented. Kevin