linux-kernel - Re: [PATCH 12/21] usb: chipidea: msm: Keep device runtime enabled

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Message-ID: <20160701032052.GG18426@shlinux2>
Date:	Fri, 1 Jul 2016 11:20:52 +0800
From:	Peter Chen <hzpeterchen@...il.com>
To:	Stephen Boyd <stephen.boyd@...aro.org>
Cc:	linux-usb@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
	Andy Gross <andy.gross@...aro.org>,
	Bjorn Andersson <bjorn.andersson@...aro.org>,
	Neil Armstrong <narmstrong@...libre.com>,
	Arnd Bergmann <arnd@...db.de>, Felipe Balbi <balbi@...nel.org>,
	Peter Chen <peter.chen@....com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-pm@...r.kernel.org
Subject: Re: [PATCH 12/21] usb: chipidea: msm: Keep device runtime enabled

On Thu, Jun 30, 2016 at 01:30:54PM -0700, Stephen Boyd wrote:
> Quoting Peter Chen (2016-06-29 18:39:01)
> > On Wed, Jun 29, 2016 at 05:43:30PM -0700, Stephen Boyd wrote:
> > > Quoting Peter Chen (2016-06-28 23:46:00)
> > > > On Sun, Jun 26, 2016 at 12:28:29AM -0700, Stephen Boyd wrote:
> > > > > Sometimes the usb wrapper device is part of a power domain that
> > > > > needs to stay on as long as the device is active. Let's get and
> > > > > put the device in driver probe/remove so that we keep the power
> > > > > domain powered as long as the device is attached. We can fine
> > > > > tune this later to handle wakeup interrupts, etc. for finer grain
> > > > > power management later, but this is necessary to make sure we can
> > > > > keep accessing the device right now.
> > > > 
> > > > Since some of the controllers work abnormal if we enables runtime
> > > > pm unconditionally, so I use one system flag CI_HDRC_SUPPORTS_RUNTIME_PM
> > > > for it. I can't understand why you can't access device without enable
> > > > parent's runtime pm, the controller will not enter runtime suspend
> > > > without that flag.
> > > 
> > > Correct, the child device of ci_hdrc_msm will be able to do runtime PM
> > > and keep the parent enabled if the CI_HDRC_SUPPORTS_RUNTIME_PM flag is
> > > set. But even if that flag isn't set, the ci_hdrc_msm driver is calling
> > > pm_runtime_enable() on the same device that it would be called on if the
> > > CI_HDRC_SUPPORTS_RUNTIME_PM flag was set. That allows runtime PM
> > > transition of child devices such as the usb ports (usb1-port1 for
> > > example) to propagate up all the way to the ci_hdrc_msm device and
> > > disable any attached power domains.
> > 
> > Sorry, I can't get you.
> > 
> > If the chipidea core's runtime is disabled, the port under the
> > controller will not be in runtime suspended, only the bus will
> > be in suspended due to USB core enables runtime PM by default.
> 
> Hmm sorry, I was confused too.
> 
> From what I can tell, if I don't call pm_runtime_set_active() on the
> glue device, it will runtime suspend once I call pm_runtime_enable() on
> it (which we do in ci_hdrc_mms_probe()). When we runtime suspend the
> glue device, we turn off the power domain associated with it too. The
> runtime pm enabled state of the core device doesn't seem to matter
> either way here. So perhaps I should be calling pm_runtime_set_active()
> before pm_runtime_enable() there instead of doing the get/put? It isn't
> clear to me when we should be calling pm_runtime_get() vs.
> pm_runtime_set_active() though.
> 
> > 
> > > 
> > > Why don't we call runtime PM functions on the ci->dev for all cases of
> > > ci->supports_runtime_pm? It seems like the glue drivers should be
> > > managing their own device power states and the ci->dev should be managed
> > > by core.c code.
> > > 
> > 
> > This is current design. Chipidea core manages portsc.phcd and PHY's PM
> > (through PHY's API), and glue layer manages its own clocks on the system
> > bus for register visit (and data transfer if necessary).
> > 
> 
> Sorry, I mean this code in core.c
> 
> 	pm_runtime_set_active(&pdev->dev);
> 	pm_runtime_enable(&pdev->dev);
>        	pm_runtime_set_autosuspend_delay(&pdev->dev, 2000);
>        	pm_runtime_mark_last_busy(ci->dev);
>        	pm_runtime_use_autosuspend(&pdev->dev);
> 
> which confused me. I thought pdev->dev was the glue device, but it's the
> same as ci->dev, the core device. I get it now, but I'd like to change
> all the calls there to use ci->dev to be clearer.

Yes, please do it.

Glue device is the parent for core device, and at core.c, only ci_hdrc_add_device and
ci_get_platdata will touch glue device.

-- 

Best Regards,
Peter Chen