Hi Mauro Thanks for your comments. On Mon, 8 Feb 2010, Mauro Carvalho Chehab wrote: > Guennadi Liakhovetski wrote: > > To save power soc-camera powers subdevices down, when they are not in use, > > if this is supported by the platform. However, the V4L standard dictates, > > that video nodes shall preserve configuration between uses. This requires > > runtime power management, which is implemented by this patch. It allows > > subdevice drivers to specify their runtime power-management methods, by > > assigning a type to the video device. > > It seems a great idea to me. For sure we need some sort of power management > control. Agree;) > > Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@xxxxxx> > > --- > > > > I've posted this patch to linux-media earlier, but I'd also like to get > > comments on linux-pm, sorry to linux-media falks for a duplicate. To > > explain a bit - soc_camera.c is a management module, that binds video > > interfaces on SoCs and sensor drivers. The calls, that I am adding to > > soc_camera.c shall save and restore sensor registers before they are > > powered down and after they are powered up. > > > > diff --git a/drivers/media/video/soc_camera.c b/drivers/media/video/soc_camera.c > > index 6b3fbcc..53201f3 100644 > > --- a/drivers/media/video/soc_camera.c > > +++ b/drivers/media/video/soc_camera.c > > @@ -24,6 +24,7 @@ > > #include <linux/mutex.h> > > #include <linux/module.h> > > #include <linux/platform_device.h> > > +#include <linux/pm_runtime.h> > > #include <linux/vmalloc.h> > > > Hmm... wouldn't it be better to enable it at the subsystem level? We may for > example call ? > The subsystem can call vidioc_streamoff() at suspend and vidioc_streamon() at > resume, if the device were streaming during suspend. We may add another ops to > the struct for the drivers/subdrivers that needs additional care. > > That's said, it shouldn't be hard to implement some routine that will save/restore > all registers if the device goes to power down mode. Unfortunately, very few > devices successfully recovers from hibernation if streaming. One good example > is saa7134, that even disables/re-enables IR IRQ's during suspend/resume. To clarify a bit - this patch implements not static PM, but dynamic (runtime) power-management. In this case it means, we are trying to save power while the system is running, but we know, that the sensor is not needed. Specifically, as long as no application is holding the video device open. And this information is only available at the bridge driver (soc-camera core) level - there is no subdev operation for open and close calls, so, subdevices do not "know" whether they are in use or not. So, only saving / restoring registers when streaming is not enough. Static PM will also be interesting - as it has been mentioned before, we will have to be careful, because sensors "sit" on two busses - i2c and video. So, you have to resume after both are up and suspend before the first of them goes down... So, that will be a different exciting topic;) Thanks Guennadi --- Guennadi Liakhovetski, Ph.D. Freelance Open-Source Software Developer http://www.open-technology.de/ -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
