Em Tue, 29 Aug 2017 10:39:52 +0200 Hans Verkuil <hverkuil@xxxxxxxxx> escreveu: > On 29/08/17 10:31, Ramesh Shanmugasundaram wrote: > > Hi Hans, > > > >> On 28/08/17 12:30, Mauro Carvalho Chehab wrote: > >>> Em Mon, 28 Aug 2017 12:05:06 +0200 > >>> Hans Verkuil <hverkuil@xxxxxxxxx> escreveu: > >>> > >>>> On 26/08/17 13:53, Mauro Carvalho Chehab wrote: > >>>>> The documentation doesn't mention if vdev-centric hardware control > >>>>> would have subdev API or not. > >>>>> > >>>>> Add a notice about that, reflecting the current status, where three > >>>>> drivers use it, in order to support some subdev-specific controls. > >>>> > >>>> I posted a patch removing v4l-subdevX support for cobalt. It's only > >>>> used within Cisco, so this is safe to do and won't break any userspace > >> support. > >>> > >>> OK. > >>> > >>>> atmel-isc is another driver that creates subdev nodes. Like cobalt, > >>>> this is unnecessary. There are no sensors that use private controls. > >>> > >>> The question is not if the driver has private controls. Private > >>> controls can be V4L2 device node oriented. > >>> > >>> The real question is if userspace applications use subdevs or not in > >>> order to set something specific to a subdev, on a pipeline where > >>> multiple subdevs could use the same control. > >>> > >>> E. g. even on a simple case where the driver would have something like: > >>> > >>> sensor -> processing -> DMA > >>> > >>> both "sensor" and "processing" could provide the same control (bright, > >>> contrast, gain, or whatever). Only by exposing such control via subdev > >>> is possible to pinpoint what part of the hardware pipeline would be > >>> affected when such control is changed. > >> > >> In theory, yes. In practice this does not happen for any of the V4L2- > >> centric drivers. Including for the three drivers under discussion. > >> > >>> > >>>> This driver is not referenced anywhere (dts or board file) in the > >> kernel. > >>>> It is highly unlikely anyone would use v4l-subdevX nodes when there > >>>> is no need to do so. My suggestion is to add a kernel option for this > >>>> driver to enable v4l-subdevX support, but set it to 'default n'. > >>>> Perhaps with a note in the Kconfig description and a message in the > >>>> kernel log that this will be removed in the future. > >>>> > >>>> The final driver is rcar_drif that uses this to set the "I2S Enable" > >>>> private control of the max2175 driver. > >>>> > >>>> I remember that there was a long discussion over this control. I > >>>> still think that there is no need to mark this private. > >>> > >>> The problem with I2S is that a device may have multiple places where > >>> I2S could be used. I don't know how the rcar-drif driver uses it, but > >>> there are several vdev-centric boards that use I2S for audio. > >>> > >>> On several of the devices I worked with, the I2S can be enabled, in > >>> runtime, if the audio signal would be directed to some digital output, > >>> or it can be disabled if the audio signal would be directed to some > >>> analog output. Thankfully, on those devices, I2S can be indirectly > >>> controlled via either an ALSA mixer or via VIDIOC A/V routing ioctls. > >>> Also, there's just one I2S bus on them. > >>> > >>> However, on a device that have multiple I2S bus, userspace should be > >>> able to control each of them individually, as some parts of the > >>> pipeline may require it enabled while others may require it disabled. > >>> So, I strongly believe that this should be a subdev control on such > >>> hardware. > >>> > >>> That's said, I don't know how rcar_drif uses it. If it has just one > >>> I2S bus and it is used only for audio, then VIDIOC A/V routing ioctls > >>> and/or an ALSA mixer could replace it. If not, then it should be kept > >>> as-is and the driver would need to add support for MC, in order for > >>> applications to identify the right sub-devices that are associated > >>> with the pipelines where I2S will be controlled. > >> > >> Ramesh, do applications using rcar_drif + max2175 have to manually enable > >> the i2s? Shouldn't this be part of the device tree description instead? > >> > > > > Yes, applications have to control this explicitly. It is not only enable but also disable control is used at run time and hence DT is not applicable. > > > > rcar_drif has two registers to write to enable rx on two data pins. It expects a sequence where the master stops output (in this max2175 i2s output - disable) - enable rcar_drif rx and then the master starts output (max2175 i2s output - enable). The application ensures this sequence today. It is one I2S bus and it is not used for audio but raw I/Q samples from max2175 tuner. > > > > The v4l2_subdev_tuner_ops does not have .s_stream api as in v4l2_subdev_video_ops and v4l2_subdev_audio_ops. If we plan to have one this functionality may be hidden inside it and no need for an explicit control. I too do not like a private control option. > > I think it would be reasonable to use the audio ops s_stream for this. We're > streaming data after all. The audio ops most closely fits what we want to do. > > All this is an internal API, so can be changed in the future if needed. > > I like that a lot better than this weird control. Yeah, I'm all in favor of implicitly control it. > > What do you think, Mauro? Right now, we have .s_stream on both audio and video. I guess we could just move it to v4l2_subdev_core_ops, as all subdevs may provide a way to start streaming. Are there any reason why we have separate s_stream callbacks right now? Thanks, Mauro -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
