Re: [PATCH v2 27/66] media: sun6i-csi: Add media ops with link notify callback

From: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
To: Sakari Ailus <sakari.ailus@linux.intel.com>
Cc: linux-media@vger.kernel.org, devicetree@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-sunxi@lists.linux.dev, linux-kernel@vger.kernel.org,
	linux-phy@lists.infradead.org, linux-clk@vger.kernel.org,
	linux-staging@lists.linux.dev, Yong Deng <yong.deng@magewell.com>,
	Mauro Carvalho Chehab <mchehab@kernel.org>,
	Rob Herring <robh+dt@kernel.org>,
	Maxime Ripard <mripard@kernel.org>,
	Hans Verkuil <hans.verkuil@cisco.com>,
	Chen-Yu Tsai <wens@csie.org>,
	Jernej Skrabec <jernej.skrabec@gmail.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Helen Koike <helen.koike@collabora.com>,
	Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
	Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Subject: Re: [PATCH v2 27/66] media: sun6i-csi: Add media ops with link notify callback
Date: Tue, 15 Feb 2022 11:01:04 +0100	[thread overview]
Message-ID: <Ygt54MQ/Nnaf4F0f@aptenodytes> (raw)
In-Reply-To: <YgqGGJJ0oVQgRoNy@paasikivi.fi.intel.com>

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Hi Sakari,

On Mon 14 Feb 22, 18:40, Sakari Ailus wrote:
> Hi Paul,
> 
> Thanks for the update.
> 
> On Sat, Feb 05, 2022 at 07:53:50PM +0100, Paul Kocialkowski wrote:
> > In order to keep the power use count fields balanced when link changes
> > happen between v4l2_pipeline_pm_get/set calls (in open/close),
> > the link_notify media operation callback needs to be registered.
> > 
> > Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
> > ---
> >  drivers/media/platform/sunxi/sun6i-csi/sun6i_csi.c | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> > 
> > diff --git a/drivers/media/platform/sunxi/sun6i-csi/sun6i_csi.c b/drivers/media/platform/sunxi/sun6i-csi/sun6i_csi.c
> > index 6f04f86504bf..c8fe31cc38b5 100644
> > --- a/drivers/media/platform/sunxi/sun6i-csi/sun6i_csi.c
> > +++ b/drivers/media/platform/sunxi/sun6i-csi/sun6i_csi.c
> > @@ -23,6 +23,7 @@
> >  #include <linux/sched.h>
> >  #include <linux/sizes.h>
> >  #include <linux/slab.h>
> > +#include <media/v4l2-mc.h>
> >  
> >  #include "sun6i_csi.h"
> >  #include "sun6i_csi_reg.h"
> > @@ -574,6 +575,12 @@ void sun6i_csi_set_stream(struct sun6i_csi_device *csi_dev, bool enable)
> >  			   CSI_CAP_CH0_VCAP_ON);
> >  }
> >  
> > +/* Media */
> > +
> > +static const struct media_device_ops sun6i_csi_media_ops = {
> > +	.link_notify = v4l2_pipeline_link_notify,
> 
> Do you really need this?
> 
> Drivers should instead rely on runtime PM nowadays.
> 
> <URL:https://hverkuil.home.xs4all.nl/spec/driver-api/camera-sensor.html#power-management>

See my remark on the patch adding support for runtime pm.

My understanding is that the callback is required when v4l2_pipeline_pm_get/set
is used, to keep the use count balanced (as mentionned in this commit message):
<https://hverkuil.home.xs4all.nl/spec/driver-api/v4l2-mc.html#c.v4l2_pipeline_pm_get>

Cheers,

Paul

> > +};
> > +
> >  /* V4L2 */
> >  
> >  static int sun6i_csi_link_entity(struct sun6i_csi_device *csi_dev,
> > @@ -683,6 +690,7 @@ static int sun6i_csi_v4l2_setup(struct sun6i_csi_device *csi_dev)
> >  	snprintf(media_dev->bus_info, sizeof(media_dev->bus_info),
> >  		 "platform:%s", dev_name(dev));
> >  	media_dev->hw_revision = 0;
> > +	media_dev->ops = &sun6i_csi_media_ops;
> >  	media_dev->dev = dev;
> >  
> >  	media_device_init(media_dev);
> 
> -- 
> Kind regards,
> 
> Sakari Ailus

-- 
Paul Kocialkowski, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com

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