[PATCH RFC 2/2] media: i2c: ov5693: fix horizontal flip polarity and Bayer phase

[Jakob Berg Jespersen]

Like the ov8865 (see previous patch), the ov5693's native readout is
horizontally mirrored and the FORMAT2 FLIP_HORZ bits (reg 0x3821)
un-mirror it: with the bits cleared the image is mirrored, with them set
it is not. The vendor init table sets the bits by default (0x3821 =
0x1e). The driver maps V4L2_CID_HFLIP=1 to setting the bits, so
requesting a flip produces an unflipped image and vice versa.

This is user-visible on the Surface Pro 7+ front camera (mounted with a
180 degree rotation, SSDB degree=180): libcamera requests HFLIP=1+VFLIP=1
to undo the mount rotation and gets a horizontally flipped image.

Verified the same way as the ov8865, with a live 4-state flip/image
matrix on the streaming sensor giving the same result: an inverted HFLIP
with a correct VFLIP.

Invert the polarity so HFLIP=0 yields the unflipped image (bits set) and
HFLIP=1 the flipped one (bits cleared).

Clearing the bits also shifts the Bayer sampling by one column: the
fixed SBGGR10 mbus code the driver reports is only correct for the
bits-set orientation, so the HFLIP=1 state has the wrong colors.
Compensate by shifting the ISP output window (reg 0x3810) one column in
that state only: OFFSET_START_X = 1 when HFLIP=1, 0 otherwise. There is
a spare column to shift into because the crop end is programmed
inclusively (crop end = crop start + width). Validated on the SP7+:
correct geometry and colors in both flip states.

Signed-off-by: Jakob Berg Jespersen <dev@xxxxxxx>
---
 drivers/media/i2c/ov5693.c | 22 +++++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)

diff --git a/drivers/media/i2c/ov5693.c b/drivers/media/i2c/ov5693.c
index 4cc796bbee92..95dc6af45125 100644
--- a/drivers/media/i2c/ov5693.c
+++ b/drivers/media/i2c/ov5693.c
@@ -375,8 +375,28 @@ static int ov5693_flip_horz_configure(struct ov5693_device *ov5693,
 		  OV5693_FORMAT2_FLIP_HORZ_SENSOR_EN;
 	int ret;
 
+	/*
+	 * The sensor's native readout is horizontally mirrored; the
+	 * FLIP_HORZ bits un-mirror it. Map the control so that HFLIP=0
+	 * yields an unmirrored image (verified on Surface Pro 7+ front
+	 * camera by a live flip-control/image matrix test, matching the
+	 * same behaviour found on the ov8865).
+	 */
 	ret = cci_update_bits(ov5693->regmap, OV5693_FORMAT2_REG, bits,
-			      enable ? bits : 0, NULL);
+			      enable ? 0 : bits, NULL);
+	if (ret)
+		return ret;
+
+	/*
+	 * Clearing the FLIP_HORZ bits shifts the Bayer sampling by one
+	 * column relative to the orientation the init table (0x3821 = 0x1e)
+	 * and the reported SBGGR10 mbus code assume, which corrupts colors.
+	 * Offset the ISP output window by one column in that state to keep
+	 * the BGGR phase; the crop window always has one spare column
+	 * (crop end = start + width, inclusive).
+	 */
+	ret = cci_write(ov5693->regmap, OV5693_OFFSET_START_X_REG,
+			enable ? 1 : 0, NULL);
 	if (ret)
 		return ret;
 

-- 
2.55.0