Re: [PATCH v2] media: ov5640: Use runtime PM

From: Sakari Ailus <sakari.ailus@linux.intel.com>
To: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Paul Elder <paul.elder@ideasonboard.com>,
	Steve Longerbeam <slongerbeam@gmail.com>,
	Hans Verkuil <hverkuil-cisco@xs4all.nl>,
	"Paul J. Murphy" <paul.j.murphy@intel.com>,
	Martina Krasteva <martinax.krasteva@intel.com>,
	Shawn Tu <shawnx.tu@intel.com>, Arec Kao <arec.kao@intel.com>,
	Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>,
	Jimmy Su <jimmy.su@intel.com>,
	Martin Kepplinger <martink@posteo.de>,
	Daniel Scally <djrscally@gmail.com>,
	Jacopo Mondi <jmondi@jmondi.org>,
	Paul Kocialkowski <paul.kocialkowski@bootlin.com>,
	linux-media@vger.kernel.org
Subject: Re: [PATCH v2] media: ov5640: Use runtime PM
Date: Mon, 14 Mar 2022 23:11:18 +0200	[thread overview]
Message-ID: <Yi+vdvMeXqb/BvKo@paasikivi.fi.intel.com> (raw)
In-Reply-To: <Yi+gEVB0FuOcY5qn@pendragon.ideasonboard.com>

Hi Laurent,

On Mon, Mar 14, 2022 at 10:05:37PM +0200, Laurent Pinchart wrote:
...
> > > Yes, after reading the version register (or doing any other harware
> > > access). Actually the full code would be
> > > 
> > > 
> > >  	pm_runtime_enable(dev);
> > >  	pm_runtime_resume_and_get(dev);
> > > 
> > > 	/* Hardware access */
> > > 
> > > 	pm_runtime_set_autosuspend_delay(dev, 1000);
> > > 	pm_runtime_use_autosuspend(dev);
> > > 	pm_runtime_put_autosuspend(dev);
> > > 
> > > (plus error handling).
> > > 
> > > If the probe function doesn't need to access the hardware, then
> > > the above becomes
> > > 
> > > 	pm_runtime_enable(dev);
> > > 	pm_runtime_set_autosuspend_delay(dev, 1000);
> > > 	pm_runtime_use_autosuspend(dev);
> > > 
> > > instead of having to power up the device just in case !PM.
> > > 
> > > > Also the latter only works on DT-based systems so it's not an option for
> > > > most of the drivers.
> > > 
> > > How so, what's wrong with the above for ACPI-based system ?
> > 
> > I²C devices are already powered on for probe on ACPI based systems.
> 
> Not through RPM I suppose ?

Runtime PM isn't involved, this takes place in the ACPI framework (via
dev_pm_domain_attach() called in i2c_device_probe()).

-- 
Regards,

Sakari Ailus