Guennadi Liakhovetski wrote: > 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. Ok. > 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;) In fact, on all drivers, there are devices that needs to be turn on only when streaming is happening: sensors, analog TV/audio demods, digital demods. Also, a few devices (for example: TV tuners) could eventually be on power off when no device is opened. As the V4L core knows when this is happening (due to open/close/poll/streamon/reqbuf/qbuf/dqbuf hooks, I think the runtime management can happen at V4L core level. > > Thanks > Guennadi > --- > Guennadi Liakhovetski, Ph.D. > Freelance Open-Source Software Developer > http://www.open-technology.de/ -- Cheers, Mauro -- 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
