Samsung camera: mystery registers investigation

Not to spam random threads, this is the one with ongoing research. Mostly regarding how to get rid of noise in the pictures.

Related: https://source.puri.sm/Librem5/linux-next/-/merge_requests/396/diffs#note_157948

https://source.puri.sm/Librem5/linux-next/-/issues/317

added camera label

mentioned in issue #317

Left part - all registers from !396 and !378 (merged) applied

Right part - same thing as above but with:

root@dogwood:/sys/kernel/debug/s5k3l6# echo 0x307b > address 
root@dogwood:/sys/kernel/debug/s5k3l6# echo 0x80 > add_value 

Taken at full res (no binning)

Well, that's curious, the banding is vertical in all my pictures. Sensor model difference?

Sorry, the photo is rotated 90 degrees (took it with Megapixels)

Also, I cropped it to show only top half to keep image size at bay.

Ah, thanks. So it's really bands parallel to the short side of the sensor.

First suspect: 0x3074, namely the last nibble (low nibble of 0x3075): by default it's 0x4.

• It seems it affects color channels separately.
• 0x1 somewhat corresponds to white when 4-binning.
• Not setting it causes a global unevenness.
• Value resulting in uniform darkness depends on binning (0x4 for 4-binning, 0x2 for 2-binning, ? (investigating) for no binning.
• 0x2 in 2-binning still leaves some banding

There seems to be some... edge detection (?) going on. With 3074: 0970, post-processing x32 it results in clumped pixels, and more clumped on edges of the radiator ribs:

For no binning, the value 0x0973 and 0x0977 work, with the latter being somewhat brighter.

There's also another set of mystery registers on page 26 of the application note:

s32020080
s32040080
s32060080
s32080080
s32320000
s32340000
s32A00100
s33000001
s34000001
s34024E00
s32680000

purism@dogwood:~$ sudo i2ctransfer -f -y 3 w2@0x2D 0x32 0x02 r2
0x00 0x81
purism@dogwood:~$ sudo i2ctransfer -f -y 3 w2@0x2D 0x32 0x04 r2
0x00 0x81
purism@dogwood:~$ sudo i2ctransfer -f -y 3 w2@0x2D 0x32 0x06 r2
0x00 0x81
purism@dogwood:~$ sudo i2ctransfer -f -y 3 w2@0x2D 0x32 0x08 r2
0x00 0x81
purism@dogwood:~$ sudo i2ctransfer -f -y 3 w2@0x2D 0x32 0x32 r2
0x00 0x40
purism@dogwood:~$ sudo i2ctransfer -f -y 3 w2@0x2D 0x32 0x34 r2
0x01 0x00
purism@dogwood:~$ sudo i2ctransfer -f -y 3 w2@0x2D 0x32 0xa0 r2
0x00 0x04
purism@dogwood:~$ sudo i2ctransfer -f -y 3 w2@0x2D 0x33 0x00 r2
0x00 0x00
purism@dogwood:~$ sudo i2ctransfer -f -y 3 w2@0x2D 0x34 0x00 r2
0x00 0x00
purism@dogwood:~$ sudo i2ctransfer -f -y 3 w2@0x2D 0x34 0x02 r2
0x4e 0x46
purism@dogwood:~$ sudo i2ctransfer -f -y 3 w2@0x2D 0x32 0x68 r2
0x01 0x00

Interestingly, the Android driver doesn't seem to touch most of those (at least I did not find them being touched anywhere). The only ones it does touch are 0x3400 and 0x3402, but they're set to 0x0000 and 0x4E42 respectively.

I'm not sure what happened, but this is what focus pixels look like now. Needless to say, this is very wrong.

Setting 3232 to 0000 from 0040 makes those look normal:

(Both pictures from test pattern).

Setting 3234 from 0100 to 0000 makes them disappear altogether.

I can't get focus pixels to appear in 1:2 binning, even though I didn't touch anything I can remember. I'm not sure whether I actually observed them.

Using cfee358d they appear in 1:1.

307a: 0d00 // default 0d80. 0080 off is noisy. Does not turn off focus pixels when binning is off. Not sure when 1:2 binning, as they don't appear.

Correction: focus pixels don't appear in 1:2 test pattern. They do appear in dark frame, although faintly.

307a: 0d00 // 0d80 0080 off is noisy. Does not affect focus pixels when binning is off. Does make them disappear in non-test-pattern 1:2 dark frames.

3074 was promising at default gain, but after bumping gain, I couldn't find any value that didn't result in banding between 0-7 at binning 2. It did change some noise and the intensity of the focus pixels at default gain:

//3074: 0977 // 0974 // 7,6,5 faint focus pixels at 2 times binning pedestal 0

//3074: 0972 // 0974 // super faint focus pixels at 2 times binning pedestal 13

//3074: 0971 // 0974 // super faint noise at 2 times binning pedestal 13

3074: 0970 // 0974 // some noise at 2 times binning pedestal 5

removed camera label

added logbook label