Em 25-06-2011 11:02, Hans Verkuil escreveu: > Hi all, > > The tuner-core.c implementation does this at the start of g_tuner: > > if (check_mode(t, vt->type) == -EINVAL) > return 0; > vt->type = t->mode; > > The idea is that the vt->type is set depending on whether the VIDIOC_G_TUNER > ioctl is called from a radio device node or a video device node. If we have a > tuner that can do both radio and TV, then the type is set to whatever the > current tuner mode is. > > This seems reasonable, but it will actually run into problems when g_tuner > is called for audio demodulators like msp3400 or cx25840. These need to know > the correct vt->type in order to fill in the right fields. > > The problem here is that the tuner subdevices are not necessarily called first. > In fact, the msp3400/cx25840 are actually called first by ivtv. > > So the msp3400 will get called with type TV, and later the tuner may change that > to type RADIO. This causes inconsistencies. This has actually been observed when > testing with ivtv and a PVR-500. > > There are two solutions: > > 1) Audit the drivers and ensure that the tuner subdevices are registered first. > > 2) Do not allow the tuner to switch the type. (2) is the right thing to do. A VIDIOC_GET_foo should not change anything. They are supposed to be read only access. > > The problem with 1 is that this will be hard to enforce in the long term. Another > problem with 1 is that I do think it is a bit unexpected from an application PoV > that the type is suddenly inconsistent with the node the ioctl is called from. > > The problem with 2 is that some sensible defaults need to be filled in if the > a radio/TV tuner is called with vt->type set to a different mode than the current > mode. > > I do not think that is very hard though: afc/signal can be 0, ditto for rxsubchans. > The audmode field should just report the value last set with s_tuner. > > g_frequency has the same problem as g_tuner. I believe g_frequency shouldn't change > the type either. Since it already has the last set frequency for tv or radio it can > just report it. > > I think the second solution is the easiest to implement and the most intuitive as > well. > > Comments? > > Hans > -- > 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 -- 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
