Hi Jacopo, On Mon, Oct 24, 2022 at 02:31:05PM +0200, Jacopo Mondi wrote: > Hi Dave, > > On Mon, Oct 24, 2022 at 01:13:58PM +0100, Dave Stevenson wrote: > > Hi Jacopo > > > > On Sat, 22 Oct 2022 at 11:47, Jacopo Mondi <jacopo@xxxxxxxxxx> wrote: > > > > > > Add support for V4L2_CID_ANALOG_GAIN. The control programs the global > > > gain register which applies to all color channels. > > > > > > Signed-off-by: Jacopo Mondi <jacopo@xxxxxxxxxx> > > > --- > > > drivers/media/i2c/ar0521.c | 16 ++++++++++++++++ > > > 1 file changed, 16 insertions(+) > > > > > > diff --git a/drivers/media/i2c/ar0521.c b/drivers/media/i2c/ar0521.c > > > index 0daa61df2603..ba169f0218a9 100644 > > > --- a/drivers/media/i2c/ar0521.c > > > +++ b/drivers/media/i2c/ar0521.c > > > @@ -35,6 +35,11 @@ > > > #define AR0521_HEIGHT_BLANKING_MIN 38u /* must be even */ > > > #define AR0521_TOTAL_WIDTH_MIN 2968u > > > > > > +#define AR0521_ANA_GAIN_MIN 0x00 > > > +#define AR0521_ANA_GAIN_MAX 0x3f > > > > The register reference I have says it is u3.4 format, which would make > > the max value 0x7f rather than 0x3f. > > > > Functionally it makes no real difference, but a max gain of nearly x7 > > 15/16ths is preferable to nearly x3 15/16ths. > > > > If it is u3.4 I'd have expected the minimum to be 0x10 to avoid a gain > > of less than x1 (does it even work?) > > > > The value of the 0x3280 register is written in the 7 low bits of the > 0x305e register. Whatever is written to 0x305e is similalrly reflected > in the 0x3280 one. The 0x305e[6:4] bits are the coarse analog gain > value and the lower 4 bits are the fine analog gain value. I wonder if > u3.4 is used there to describe the that, even if u3.4 has a different > meaning > > > Looking at the listed m0, c0, m1, c1 values for gain (1, 0, 0, and 4 > > respectively), that maps to a formula: > > gain = code / 4 > > Min and max codes are 0 and 0x1f, so that implies it will do a gain of > > less than x1, and goes up to x7.75. > > The sensor does not use the CCS gain model, but an exponential > piecewise function documented as a table of register values/gains in > the application manual. > > The sensor exposes a list of CCS-compatible registers, including > "0x0204 analogue_gain_code_global", from which I presume one should > contorl the gain if the CCS compatible model works. From my tests, > writing to that register is a no-op. > > I presume the CCS compatible interface is not plumbed, or maybe it > depdends on the FW version, or else :) It is also possible this is a sensor developed based on an earlier one that was compatible with e.g. SMIA. If the newer CCS-only registers aren't defined, it is unlikely it would be compatible. -- Regards, Sakari Ailus Ps. this would be a good time to get patches towards upstream. :-)
