[PATCH] media: i2c: ov02c10: tolerate a sensor clock other than 19.2 MHz

[Ryan Thomas Cragun]

The driver requires the sensor's external clock to be exactly 19.2 MHz
(OV02C10_MCLK) and aborts probe with -EINVAL otherwise. This leaves the
camera completely unusable on platforms that clock the sensor
differently.

For example, the Microsoft Surface Laptop 7 (Intel) drives the OV02C10
from a fixed 12 MHz clock (provided by an INT3472 "discrete" clock that
cannot be reprogrammed). The sensor's register/PLL tables assume 19.2
MHz, so at 12 MHz all timings scale by 12/19.2 (the nominal 30 fps mode
runs at ~18.75 fps), but the sensor is otherwise fully functional and
produces a correct image.

Rather than failing probe:

 - Attempt clk_set_rate(OV02C10_MCLK). On platforms whose sensor clock is
   programmable (e.g. a TPS68470 PMIC) this yields the expected 19.2 MHz
   and the native frame rate.
 - If the rate still differs (fixed clock), warn and continue instead of
   aborting, so the camera works.

Platforms that already provide 19.2 MHz are unaffected (no warning, no
rate change). The reduced frame rate on a lower clock can be restored by
shrinking the sensor's vertical blanking (VTS); that can be addressed
separately.

Signed-off-by: Ryan Thomas Cragun <ryantcragun@xxxxxxxxx>
---
 drivers/media/i2c/ov02c10.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/drivers/media/i2c/ov02c10.c b/drivers/media/i2c/ov02c10.c
index cf93d3603..01cbaedfc 100644
--- a/drivers/media/i2c/ov02c10.c
+++ b/drivers/media/i2c/ov02c10.c
@@ -892,10 +892,19 @@ static int ov02c10_probe(struct i2c_client *client)
 				     "failed to get imaging clock\n");
 
 	freq = clk_get_rate(ov02c10->img_clk);
+	if (freq != OV02C10_MCLK) {
+		/*
+		 * Some platforms provide the sensor clock via a programmable
+		 * PMIC. Ask for OV02C10_MCLK; if that is not possible (e.g. a
+		 * fixed 12 MHz clock on the Surface Laptop 7) proceed anyway.
+		 */
+		if (clk_set_rate(ov02c10->img_clk, OV02C10_MCLK) == 0)
+			freq = clk_get_rate(ov02c10->img_clk);
+	}
 	if (freq != OV02C10_MCLK)
-		return dev_err_probe(ov02c10->dev, -EINVAL,
-				     "external clock %lu is not supported",
-				     freq);
+		dev_warn(ov02c10->dev,
+			 "external clock %lu differs from expected %u; proceeding anyway\n",
+			 freq, OV02C10_MCLK);
 
 	v4l2_i2c_subdev_init(&ov02c10->sd, client, &ov02c10_subdev_ops);
 
-- 
2.43.0