On Sunday 23 May 2010, Hans Verkuil wrote: > On Saturday 22 May 2010 19:21:32 Ian Armstrong wrote: > > On Saturday 22 May 2010, Andy Walls wrote:
> > > Some thoughts: > > > > > > 1. to me it appears that the ivtv driver looks like it ties the output > > > standard to the input standard currently (probably due to some firmware > > > limitation). This need not be the case in general. > > > > The ivtv limitation is the driver and not the firmware. > > Correct. > > > The firmware itself > > seems quite happy with mixed standards & in some cases will automatically > > switch the output standard itself (resulting in a standards mismatch > > between the cx23415 & saa7127, breaking output). For the previous 2 > > months I've been running a patched version of the ivtv driver that > > separates the input & output format with no noticeable issues. > > > > > 2. currently the ivtv driver uses sepearte device nodes for input > > > device and an output device. If bridge drivers maintain that > > > paradigm, then separate ioctl()s for S_STD, G_STD, and ENUMSTD are > > > likely not needed. > > > > This is how my patched version works, talk to an input device for the > > input & an output device for the output. However, from my reading of the > > specs I do get the impression this is not the 'correct' way to do this > > and it should really be a separate ioctl. I don't know what other cards, > > if any, support mixed input & output standards or how they handle it. > > I have considered implementing these output ioctls as well and as mentioned > s_std_output is actually implemented on the subdev level (it was really > needed there). > > The reason it was never done for bridge drivers is twofold: > > 1) No one ever needed it. Why would you want to select one format for input > and another for output? Other than debugging this never happens for the > sort of drivers we have now. So selecting e.g. PAL and have it change both > input and output is actually what most people expect. There's no denying that mixed standards is unusual, but is it a case of nobody ever wanted it, or did they just assume the hardware wasn't capable of it. The only reason I ever created a patch to support mixed standards in the ivtv driver is because it was a feature which I wanted to use. In my case all captures are PAL, but I view a lot of NTSC material. I find that interlaced video looks best when displayed in its native format so I use a script to identify & change the output to match. Mixed standards allow MythTV to record a show in PAL while I'm watching an NTSC video on an NTSC output. Another instance when mixed formats would be useful is when capturing a video which doesn't match your regions standard. If I'm trying to capture an NTSC video, it doesn't mean I want the output mode changed from my native PAL. Just because the card can output NTSC doesn't mean the display can handle it. > 2) Do we really need to make new ioctls? Here it becomes hairy. According > to the V4L2 spec changing the std for one video device should change it > for all others as well. So if we follow that spec, then we should indeed > introduce new ioctls. But in practice all driver have separate device > nodes for capture and output. So perhaps we should change the spec and > specify that it will only change the std for those device nodes that are > linked to the same input or output. I doubt it's really used outside of v4l2-ctl, but the ivtv driver allows output configuration to be changed via the capture device. In this instance a new ioctl would avoid a situation where the output can only be partially configured through the capture device. In reality I doubt any application actually configures the output via the capture device, but to reuse the ioctl & link it to a specific device node would create an inconsistency. -- Ian -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
