On 05/09/2014 03:46 PM, Sakari Ailus wrote: > Hi Hans, > > On Fri, May 09, 2014 at 02:57:13PM +0200, Hans Verkuil wrote: >> On 05/08/2014 11:04 AM, Sakari Ailus wrote: >>> Heippa! >>> >>> On Wed, May 07, 2014 at 03:57:11PM +0300, Antti Palosaari wrote: >>>> What is preferred way implement controls that could have some known >>>> unit or unknown unit? For example for gain controls, I would like to >>>> offer gain in unit of dB (decibel) and also some unknown driver >>>> specific unit. Should I two controls, one for each unit? >>>> >>>> Like that >>>> >>>> V4L2_CID_RF_TUNER_LNA_GAIN_AUTO >>>> V4L2_CID_RF_TUNER_LNA_GAIN >>>> V4L2_CID_RF_TUNER_LNA_GAIN_dB >>> >>> I suppose that on any single device there would be a single unit to control >>> a given... control. Some existing controls do document the unit as well but >>> I don't think that's scalable nor preferrable. This way we'd have many >>> different controls to control the same thing but just using a different >>> unit. The auto control is naturally different. Hans did have a patch to add >>> the unit to queryctrl (in the form of QUERY_EXT_CTRL). >> >> Well, that's going to be dropped again. There were too many comments about >> that during the mini-summit and it was not critical for me. > > Ok. Thanks for the information. > >>> <URL:http://www.spinics.net/lists/linux-media/msg73136.html> >>> >>> I wish we can get these in relatively soon. >> >> Sakari, I think you will have to push this if you want this done. > > Ack. I think I proposed something like this already a few years ago so I'm > fine picking it up. :-) Now it's a good time to add the required space in > the struct as we're going to have a new IOCTL anyway. > >> One interesting thing to look at: the AVB IEEE 1722.1 standard has extensive >> support for all sorts of units. I don't know if you have access to the standard >> document, but it might be interesting to look at what they do there. > > I have access to it but I don't see this would be that interesting in > regards to what we're doing. In any case, we should document the units so > that different drivers end up using exactly the same string to signal a > particular unit. Actually, it is interesting. AVB has controls as well, and those map pretty much exactly to the sort of controls we have, and they support a wide range of units. Look at section 7.3.3 ("Control Value Units") of IEEE 1722.1. If nothing else, it gives a good insight into how others handle this. Regards, Hans > I prefer to have a prefix as well: a lot of hardware devices use binary > fractions so that even if we provide an integer control to the user the > actual control value may well be divided by e.g. 256. That is a somewhat > separate topic still. > -- 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
