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media: i2c: imx477: Correct minimum exposure lines #5050

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Jun 6, 2022
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media: i2c: imx477: Correct minimum exposure lines #5050

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2 changes: 1 addition & 1 deletion drivers/media/i2c/imx477.c
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Expand Up @@ -61,7 +61,7 @@ MODULE_PARM_DESC(trigger_mode, "Set vsync trigger mode: 1=source, 2=sink");
/* Exposure control */
#define IMX477_REG_EXPOSURE 0x0202
#define IMX477_EXPOSURE_OFFSET 22
#define IMX477_EXPOSURE_MIN 20
#define IMX477_EXPOSURE_MIN 4
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Table 5-24 Integration time setting (In case of FRM_LENGHT_CTL = 0h) appears to be fairly explicit that a COARSE_INTEG_TIME of > FRM_LENGTH_LINES - 20 is prohibited.

Also description of register 0350h FRM_LENGTH_CTL also states that it controls whether the frame length is changed when FRM_LENGTH_LINES < COARSE_INTEG_TIME + alpha, where alpha = 20 for this sensor.

Or am I getting confused here with the value that should be set in EXPOSURE_OFFSET for max exposure time? That appears that it should be 20 instead of 22.

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Yes, I agree things are not explained in the clearest way and there is some interpretation involved!

I took these various statements to be a restriction on FRM_LENGTH_LINES, but not actually implying anything about the min value of COARSE_INTEG_TIME. Indeed, in our old firmware driver it goes lower than 20 by some way (giving 114us min exposure rather than 571us).

I thought EXPOSURE_OFFSET being 22 rather than 20 was maybe a question of tests including the case of equality or not, but honestly I don't know!

#define IMX477_EXPOSURE_STEP 1
#define IMX477_EXPOSURE_DEFAULT 0x640
#define IMX477_EXPOSURE_MAX (IMX477_FRAME_LENGTH_MAX - \
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