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: Fri, 11 Mar 2022 15:15:54 +0200	[thread overview]
Message-ID: <YitLit9LC2zlOfdh@paasikivi.fi.intel.com> (raw)
In-Reply-To: <YitA0dI2mM4ACdaL@pendragon.ideasonboard.com>

Hi Laurent,

On Fri, Mar 11, 2022 at 02:30:09PM +0200, Laurent Pinchart wrote:
> Hi Sakari,
> 
> On Fri, Mar 11, 2022 at 02:23:53PM +0200, Sakari Ailus wrote:
> > On Fri, Mar 11, 2022 at 08:12:59PM +0900, Paul Elder wrote:
> > > Switch to using runtime PM for power management.
> > > 
> > > Signed-off-by: Paul Elder <paul.elder@ideasonboard.com>
> > > 
> > > ---
> > > Changes in v2:
> > > - replace manual tracking of power status with pm_runtime_get_if_in_use
> > > - power on the sensor before reading the checking the chip id
> > > - add dependency on PM to Kconfig
> > > ---
> > >  drivers/media/i2c/Kconfig  |   1 +
> > >  drivers/media/i2c/ov5640.c | 112 ++++++++++++++++++++++---------------
> > >  2 files changed, 67 insertions(+), 46 deletions(-)
> > > 
> > > diff --git a/drivers/media/i2c/Kconfig b/drivers/media/i2c/Kconfig
> > > index e7194c1be4d2..97c3611d9304 100644
> > > --- a/drivers/media/i2c/Kconfig
> > > +++ b/drivers/media/i2c/Kconfig
> > > @@ -1025,6 +1025,7 @@ config VIDEO_OV5640
> > >  	tristate "OmniVision OV5640 sensor support"
> > >  	depends on OF
> > >  	depends on GPIOLIB && VIDEO_V4L2 && I2C
> > > +	depends on PM
> > 
> > I think this is not needed as the sensor is powered on explicitly in probe.
> > 
> > You should similarly power it off explicitly in remove, set the runtime PM
> > status suspended and disable runtime PM. See e.g. imx319 driver for an
> > example. It doesn't have resume callback but that doesn't really matter ---
> > it's just ACPI-only.
> 
> Do we want to continue supporting !PM ? Does it have any real use case
> when dealing with camera sensors ?

Probably not much.

The changes I proposed are not eve related on runtime PM. Hence the
question here is whether there should be a dependency to CONFIG_PM or not,
and as there's no technical reason to have it, it should be omitted.

-- 
Kind regards,

Sakari Ailus