Hi Ping-chung, On Fri, Sep 21, 2018 at 07:08:10AM +0000, Chen, Ping-chung wrote: > Typo. > > -----Original Message----- > From: Chen, Ping-chung > Sent: Friday, September 21, 2018 3:07 PM > To: 'Ricardo Ribalda Delgado' <ricardo.ribalda@xxxxxxxxx>; Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> > Cc: Sakari Ailus <sakari.ailus@xxxxxx>; tfiga@xxxxxxxxxxxx; Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>; sylwester.nawrocki@xxxxxxxxx; linux-media <linux-media@xxxxxxxxxxxxxxx>; Yeh, Andy <andy.yeh@xxxxxxxxx>; Lai, Jim <jim.lai@xxxxxxxxx>; grundler@xxxxxxxxxxxx; Mani, Rajmohan <rajmohan.mani@xxxxxxxxx> > Subject: RE: [PATCH v5] media: imx208: Add imx208 camera sensor driver > > Hi Sakari, > > >-----Original Message----- > >From: Ricardo Ribalda Delgado [mailto:ricardo.ribalda@xxxxxxxxx] > >Sent: Friday, September 21, 2018 5:55 AM > > >HI > On Thu, Sep 20, 2018 at 11:13 PM Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> wrote: > > > > Hi Sakari, > > > > On Thursday, 20 September 2018 23:56:59 EEST Sakari Ailus wrote: > > > On Thu, Sep 20, 2018 at 05:51:55PM +0900, Tomasz Figa wrote: > > > > On Wed, Aug 8, 2018 at 4:08 PM Ping-chung Chen wrote: > > > > [snip] > > > > > > > > > + > > > > > +/* Digital gain control */ > > > > > +#define IMX208_REG_GR_DIGITAL_GAIN 0x020e > > > > > +#define IMX208_REG_R_DIGITAL_GAIN 0x0210 > > > > > +#define IMX208_REG_B_DIGITAL_GAIN 0x0212 > > > > > +#define IMX208_REG_GB_DIGITAL_GAIN 0x0214 > > > > > +#define IMX208_DGTL_GAIN_MIN 0 > > > > > +#define IMX208_DGTL_GAIN_MAX 4096 > > > > > +#define IMX208_DGTL_GAIN_DEFAULT 0x100 > > > > > +#define IMX208_DGTL_GAIN_STEP 1 > > > > > + > > > > > > > > [snip] > > > > > > > > > +/* Initialize control handlers */ static int > > > > > +imx208_init_controls(struct imx208 *imx208) { > > > > > > > > [snip] > > > > > > > > > + v4l2_ctrl_new_std(ctrl_hdlr, &imx208_ctrl_ops, > > > > > V4L2_CID_DIGITAL_GAIN, + IMX208_DGTL_GAIN_MIN, > > > > > IMX208_DGTL_GAIN_MAX, + IMX208_DGTL_GAIN_STEP, > > > > > + IMX208_DGTL_GAIN_DEFAULT); > > > > > > > > We have a problem here. The sensor supports only a discrete range > > > > of values here - {1, 2, 4, 8, 16} (multiplied by 256, since the > > > > value is fixed point). This makes it possible for the userspace to > > > > set values that are not allowed by the sensor specification and > > > > also leaves no way to enumerate the supported values. > > > > > > > > I can see two solutions here: > > > > > > > > 1) Define the control range from 0 to 4 and treat it as an > > > > exponent of 2, so that the value for the sensor becomes (1 << val) * 256. > > > > (Suggested by Sakari offline.) > > > > > > > > This approach has the problem of losing the original unit (and > > > > scale) of the value. > > > > > > I'd like to add that this is not a property of the proposed solution. > > > > > > Rather, the above needs to be accompanied by additional information > > > provided through VIDIOC_QUERY_EXT_CTRL, i.e. the unit, prefix as > > > well as other information such as whether the control is linear or > > > exponential (as in this case). > > > > > > > 2) Use an integer menu control, which reports only the supported > > > > discrete values - {1, 2, 4, 8, 16}. > > > > > > > > With this approach, userspace can enumerate the real gain values, > > > > but we would either need to introduce a new control (e.g. > > > > V4L2_CID_DIGITAL_GAIN_DISCRETE) or abuse the specification and > > > > register V4L2_CID_DIGITAL_GAIN as an integer menu. > > > > > > New controls in V4L2 are, for the most part, created when there's > > > something new to control. The documentation of some controls > > > (similar to e.g. gain) documents a unit as well as a prefix but > > > that's the case only because there's been no way to tell the unit or prefix otherwise in the API. > > > > > > An exception to this are EXPOSURE and EXPOSURE_ABSOLUTE. I'm not > > > entirely sure how they came to be though. An accident is a > > > possibility as far as I see. > > > > If I remember correctly I introduced the absolute variant for the UVC > > driver (even though git blame points to Brandon Philips). I don't > > really remember why though. > > > > > Controls that have a documented unit use that unit --- as long as > > > that's the unit used by the hardware. If it's not, it tends to be > > > that another unit is used but the user space has currently no way of > > > knowing this. And the digital gain control is no exception to this. > > > > > > So if we want to improve the user space's ability to be informed how > > > the control values reflect to device configuration, we do need to > > > provide more information to the user space. One way to do that would > > > be through VIDIOC_QUERY_EXT_CTRL. The IOCTL struct has plenty of > > > reserved fields --- just for purposes such as this one. > > > > I don't think we can come up with a good way to expose arbitrary > > mathematical formulas through an ioctl. In my opinion the question is > > how far we want to go, how precise we need to be. > > > > > > Any opinions or better ideas? > > >My 0.02 DKK. On a similar situation, where userspace was running a close loop calibration: > > >We have implemented two extra control: eposure_next exposure_pre that tell us which one is the next value. Perhaps we could embebed such functionality in QUERY_EXT_CTRL. > > >Cheers > > How about creating an additional control to handle the case of > V4L2_CID_GAIN in the imx208 driver? HAL can set AG and DG separately for > the general sensor usage by V4L2_CID_ANALOGUE_GAIN and > V4L2_CID_DIGITAL_GAIN but call V4L2_CID_GAIN for the condition of setting > total_gain=AGxDG. How do you update the two other controls if the user updates the V4L2_CID_GAIN control? -- Sakari Ailus sakari.ailus@xxxxxxxxxxxxxxx
