Hi Sakari, Laurent, everyone Thanks for the feedback. On Mon, 24 May 2021 at 02:07, Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> wrote: > > Hello, > > On Wed, May 19, 2021 at 10:01:49PM +0300, Sakari Ailus wrote: > > Added Laurent to cc. > > > > On Wed, May 19, 2021 at 10:01:21PM +0300, Sakari Ailus wrote: > > > Hi David, > > > > > > Thanks for the patch. > > > > > > Cc'ing Laurent, too. > > > > > > On Mon, May 17, 2021 at 11:02:40AM +0100, David Plowman wrote: > > > > Add documentation for each of the controls > > > > > > > > V4L2_CID_NOTIFY_GAIN_RED > > > > V4L2_CID_NOTIFY_GAIN_GREENR > > > > V4L2_CID_NOTIFY_GAIN_BLUE > > > > V4L2_CID_NOTIFY_GAIN_GREENB > > > > > > > > These controls are required by sensors that need to know what colour > > > > gains will be applied to pixels by downstream processing (such as by > > > > an ISP), though the sensor does not apply these gains itself. > > > > > > > > Signed-off-by: David Plowman <david.plowman@xxxxxxxxxxxxxxx> > > > > --- > > > > .../media/v4l/ext-ctrls-image-source.rst | 28 +++++++++++++++++++ > > > > 1 file changed, 28 insertions(+) > > > > > > > > diff --git a/Documentation/userspace-api/media/v4l/ext-ctrls-image-source.rst b/Documentation/userspace-api/media/v4l/ext-ctrls-image-source.rst > > > > index de43f5c8486d..f824d6c36ae8 100644 > > > > --- a/Documentation/userspace-api/media/v4l/ext-ctrls-image-source.rst > > > > +++ b/Documentation/userspace-api/media/v4l/ext-ctrls-image-source.rst > > > > @@ -72,3 +72,31 @@ Image Source Control IDs > > > > * - __u32 > > > > - ``height`` > > > > - Height of the area. > > > > + > > > > +``V4L2_CID_NOTIFY_GAIN_RED (integer)`` > > > > + Notify the sensor what gain will be applied to red pixels by the > > > > + subsequent processing (such as by an ISP). The sensor is merely > > > > + informed of this value in case it performs processing that requires > > > > + it, but it is not applied to the output pixels themselves. The > > > > + units are determined by the sensor driver. > > > > > > I wonder if this should say the default value should reflect gain of 1. It > > > probably wouldn't hurt at least. > > Seems reasonable to me. Yes, I think this is a good idea. > > David, do you think we could also document that the values of these > controls are linear, or would that be too restrictive ? That's an interesting point. I guess I was drawing on the precedent set by analogue gain, but in many respects mandating a linear response, and not letting device specific units escape the driver, might be more convenient for application code. The typical use would, I expect, involve firmware reading colour gains from an ISP and passing them in here. As such, linear is quite likely to be desirable. In the event that there is a conversion to be done, the driver can always take care of it. Further, if we want to go with linear values, I wonder whether we should go all the way and specify it fully. For example we could mandate u8.8 values, so that 256 means 1.0x - this already feels like more than enough range and precision. There's a slight question in my mind as to whether we should specify the range of the control too, in particular whether gains can be less than unity or not. Again, this would be kind to applications, but drivers might have to re-interpret it internally for "fussy" sensors. Any other opinions on that? One side effect of specifying the meaning precisely is that all four necessarily become identical. I hadn't mentioned this previously, but having them different would clearly be a right nuisance! If that sounds good to everyone I'll make up a second version with updated documentation. Thanks and best regards David > > > > > + > > > > +``V4L2_CID_NOTIFY_GAIN_GREENR (integer)`` > > > > + Notify the sensor what gain will be applied to green pixels (on > > > > + red rows) by subsequent processing (such as by an ISP). The sensor > > > > + is merely informed of this value in case it performs processing > > > > + that requires it, but it is not applied to the output pixels > > > > + themselves. The units are determined by the sensor driver. > > > > + > > > > +``V4L2_CID_NOTIFY_GAIN_BLUE (integer)`` > > > > + Notify the sensor what gain will be applied to blue pixels by the > > > > + subsequent processing (such as by an ISP). The sensor is merely > > > > + informed of this value in case it performs processing that requires > > > > + it, but it is not applied to the output pixels themselves. The > > > > + units are determined by the sensor driver. > > > > + > > > > +``V4L2_CID_NOTIFY_GAIN_GREENB (integer)`` > > > > + Notify the sensor what gain will be applied to green pixels (on > > > > + blue rows) by subsequent processing (such as by an ISP). The sensor > > > > + is merely informed of this value in case it performs processing > > > > + that requires it, but it is not applied to the output pixels > > > > + themselves. The units are determined by the sensor driver. > > -- > Regards, > > Laurent Pinchart
