linux-kernel - Re: [alsa-devel] [PATCH] soundwire: fix pm_runtime_get

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Message-ID: <20190414102601.GM28103@vkoul-mobl>
Date:   Sun, 14 Apr 2019 15:56:02 +0530
From:   Vinod Koul <vkoul@...nel.org>
To:     Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
Cc:     Jan Kotas <jank@...ence.com>,
        "alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        "sanyog.r.kale@...el.com" <sanyog.r.kale@...el.com>
Subject: Re: [alsa-devel] [PATCH] soundwire: fix pm_runtime_get_sync return
 code checks

On 08-04-19, 12:43, Pierre-Louis Bossart wrote:
> 
> 
> On 4/8/19 2:12 AM, Jan Kotas wrote:
> > 
> > 
> > > On 5 Apr 2019, at 17:04, Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com> wrote:
> > > 
> > > On 4/5/19 2:26 AM, Jan Kotas wrote:
> > > > 
> > > >   	ret = pm_runtime_get_sync(slave->bus->dev);
> > > > -	if (ret < 0)
> > > > +	if (ret < 0 && ret != -EACCES)
> > > > 
> > > There was a patch submitted on 3/28 by Srinivas Kandagatla who suggested an alternate solution for exactly the same code.
> > > 
> > > +	if (pm_runtime_enabled(slave->bus->dev)) {
> > > +		ret = pm_runtime_get_sync(slave->bus->dev);
> > > +		if (ret < 0)
> > > +			return ret;
> > > 
> > > I am far from an expert on pm_runtime but Srinivas' solution looks more elegant to me.
> > 
> > Hello Pierre,
> > 
> > Please take a look at this patch, that was my inspiration:
> > https://lists.linuxfoundation.org/pipermail/linux-pm/2011-June/031930.html
> 
> The two patches seems to be identical:
> 
> static inline bool pm_runtime_enabled(struct device *dev)
> {
> 	return !dev->power.disable_depth;
> }
> 
> static int rpm_resume()
> [...]
> else if (dev->power.disable_depth > 0)
> 		retval = -EACCES;
> 
> 
> However I am still not clear on why this might fail.
> 
> I can only think of one possible explanation: there is no explicit
> pm_runtime_enable() in the soundwire code, so maybe the expectation is that
> the pm_runtime status is inherited from the parent (in the intel case the
> PCI driver), and that's missing in non-intel configurations?

IIRC that needs to be called by the Intel driver and those patches were
not upstreamed. So we dont have fully supported PM on upstream yet!

> 
> > I also took a look, and it seems the value returned by
> > pm_runtime_get_syncis simply ignored in a lot of places,
> > so checking its value may be excessive.
> But not checking seems careless at best...

-- 
~Vinod