linux-kernel - Re: [PATCH 8/9] soundwire: intel: add wake interrupt support

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Message-ID: <20200701055654.GW2599@vkoul-mobl>
Date:   Wed, 1 Jul 2020 11:26:54 +0530
From:   Vinod Koul <vkoul@...nel.org>
To:     Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
Cc:     Bard Liao <yung-chuan.liao@...ux.intel.com>,
        alsa-devel@...a-project.org, linux-kernel@...r.kernel.org,
        tiwai@...e.de, broonie@...nel.org, gregkh@...uxfoundation.org,
        jank@...ence.com, srinivas.kandagatla@...aro.org,
        rander.wang@...ux.intel.com, ranjani.sridharan@...ux.intel.com,
        hui.wang@...onical.com, sanyog.r.kale@...el.com,
        slawomir.blauciak@...el.com, mengdong.lin@...el.com,
        bard.liao@...el.com
Subject: Re: [PATCH 8/9] soundwire: intel: add wake interrupt support

On 30-06-20, 12:18, Pierre-Louis Bossart wrote:
> > > +		return 0;
> > > +	}
> > > +
> > > +	shim = sdw->link_res->shim;
> > > +	wake_sts = intel_readw(shim, SDW_SHIM_WAKESTS);
> > > +
> > > +	if (!(wake_sts & BIT(sdw->instance)))
> > > +		return 0;
> > > +
> > > +	/* disable WAKEEN interrupt ASAP to prevent interrupt flood */
> > > +	intel_shim_wake(sdw, false);
> > 
> > when & where is this enabled?
> 
> in follow-up patches where the clock-stop mode is enabled.

ok

> > > +	 * wake up master and slave so that slave can notify master
> > > +	 * the wakeen event and let codec driver check codec status
> > > +	 */
> > > +	list_for_each_entry(slave, &bus->slaves, node) {
> > > +		/*
> > > +		 * discard devices that are defined in ACPI tables but
> > > +		 * not physically present and devices that cannot
> > > +		 * generate wakes
> > > +		 */
> > > +		if (slave->dev_num_sticky && slave->prop.wake_capable)
> > > +			pm_request_resume(&slave->dev);
> > 
> > Hmmm, shouldn't slave do this? would it not make sense to notify the
> > slave thru callback and then slave decides to resume or not..?
> 
> In this mode, the bus is clock-stop mode, and events are detected with level
> detector tied to PCI events. The master and slave devices are all in
> pm_runtime suspended states. The codec cannot make any decisions on its own
> since the bus is stopped, it needs to first resume, which assumes that the
> master resumes first and the enumeration re-done before it can access any of
> its registers.
> 
> By looping through the list of devices that can generate events, you end-up
> first forcing the master to resume, and then each slave resumes and can
> check who generated the event and what happened while suspended. if the
> codec didn't generate the event it will go back to suspended mode after the
> usual timeout.
> 
> We can add a callback but that callback would only be used for Intel
> solutions, but internally it would only do a pm_request_resume() since the
> codec cannot make any decisions before first resuming. In other words, it
> would be an Intel-specific callback that is implemented using generic resume
> operations. It's probably better to keep this in Intel-specific code, no?

I do not like the idea that a device would be woken up, that kind of
defeats the whole idea behind the runtime pm. Waking up a device to
check the events is a generic sdw concept, I don't see that as Intel
specific one.

I would like to see a generic callback for the devices and let devices
do the resume part, that is standard operating principle when we deal
with suspended devices. If the device thinks they need to resume, they
will do the runtime resume, check the status and sleep if not
applicable. Since we have set the parents correctly, any resume
operation for slaves would wake master up as well...

I do not see a need for intel driver to resume slave devices here, or
did I miss something?

-- 
~Vinod