media: i2c: imx477: Correct minimum exposure lines #5050
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The minimum number of exposure lines value (IMX477_EXPOSURE_MIN) was previously 20 but this is not correct. The datasheet is not completely explicit, however the new value of 4 has been tested with all the sensor modes supported by this driver, and matches the lowest exposure value of 114us that could be achieved wtih Raspberry Pi's legacy firmware driver. Signed-off-by: David Plowman <[email protected]>
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LGTM |
| @@ -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!
See: raspberrypi/linux#5041 kernel: media: i2c: imx477: Correct minimum exposure lines See: raspberrypi/linux#5050 kernel: arm64: Initialize jump labels before setup_machine_fdt()
See: raspberrypi/linux#5041 kernel: media: i2c: imx477: Correct minimum exposure lines See: raspberrypi/linux#5050 kernel: arm64: Initialize jump labels before setup_machine_fdt()
The minimum number of exposure lines value (IMX477_EXPOSURE_MIN) was
previously 20 but this is not correct. The datasheet is not completely
explicit, however the new value of 4 has been tested with all the
sensor modes supported by this driver, and matches the lowest exposure
value of 114us that could be achieved wtih Raspberry Pi's legacy
firmware driver.
Signed-off-by: David Plowman [email protected]