[PATCH v5 4/7] media: i2c: ov5693: Gate the MIPI clock lane for non-continuous clock

[Fernando Rimoli]

The ov5693 never programs MIPI_CTRL00 (0x4800), leaving it at its 0x00
power-on default, which lets the MIPI clock run freely. The IPU3 CSI-2
receiver tolerates this, but the IPU6 receiver (e.g. on Microsoft
Surface Pro 7+, Pro 8, Pro 9 and Surface Go 4) fails to lock onto the
link, so the sensor streams but capture times out with "stream stop
time out". On most affected machines no frames arrive at all; on some
the failure is intermittent.

Gate the clock lane while idle at stream on when the endpoint requests a
non-continuous clock.

Only the gate bit is touched, so platforms that do not request it are
unaffected. No counterpart is needed at stream off, as the link is down
by then and the register returns to its default when the sensor is
powered off.

The property is supplied by the ipu-bridge in a subsequent patch.

Link: https://github.com/linux-surface/linux-surface/pull/2171
Co-developed-by: Arsalan Naeem <naeemarsalan@xxxxxxxxx>
Signed-off-by: Arsalan Naeem <naeemarsalan@xxxxxxxxx>
Signed-off-by: Fernando Rimoli <fernandorimoli11@xxxxxxxxx>
Tested-by: Jakob Berg Jespersen <dev@xxxxxxx> # Surface Pro 7+, IPU6 Tiger Lake
Tested-by: Fil Dunsky <filipp.dunsky@xxxxxxxxx> # Surface Pro 8, IPU6 Tiger Lake (8086:9a19)
Tested-by: Lucas Lis <lucaseze.lis@xxxxxxxxx> # Surface Pro 7+, IPU6 Tiger Lake (0x9a19)
Tested-by: Kengo Oki <dev.kengo.fugu0141@xxxxxxxxx> # Surface Go 4, IPU6 Alder Lake-N 8086:462e
---
 drivers/media/i2c/ov5693.c | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/drivers/media/i2c/ov5693.c b/drivers/media/i2c/ov5693.c
index 02236f3db..cedc6ea03 100644
--- a/drivers/media/i2c/ov5693.c
+++ b/drivers/media/i2c/ov5693.c
@@ -35,6 +35,11 @@
 #define OV5693_STOP_STREAMING			0x00
 #define OV5693_SW_RESET				0x01
 
+/* MIPI transmitter control */
+#define OV5693_MIPI_CTRL00_REG			CCI_REG8(0x4800)
+/* Gate the clock lane when there is no packet to transmit */
+#define OV5693_MIPI_CTRL00_CLOCK_LANE_GATE	BIT(5)
+
 #define OV5693_REG_CHIP_ID			CCI_REG16(0x300a)
 /* Yes, this is right. The datasheet for the OV5693 gives its ID as 0x5690 */
 #define OV5693_CHIP_ID				0x5690
@@ -144,6 +149,9 @@ struct ov5693_device {
 	struct regulator_bulk_data supplies[OV5693_NUM_SUPPLIES];
 	struct clk *xvclk;
 
+	/* Gate the MIPI clock lane when idle (CSI-2 non-continuous clock) */
+	bool clock_ncont;
+
 	struct ov5693_mode {
 		struct v4l2_rect crop;
 		struct v4l2_mbus_framefmt format;
@@ -611,6 +619,19 @@ static int ov5693_enable_streaming(struct ov5693_device *ov5693, bool enable)
 {
 	int ret = 0;
 
+	/*
+	 * Gate the MIPI clock lane while idle if the CSI-2 link is configured
+	 * for a non-continuous clock. Only that bit is touched, and only in
+	 * that case, so the register keeps whatever the platform left in it
+	 * and the clock stays free-running as before everywhere else. It
+	 * needs no counterpart at stream off: the link is down by then, and
+	 * the register returns to its default when the sensor is powered off.
+	 */
+	if (enable && ov5693->clock_ncont)
+		cci_update_bits(ov5693->regmap, OV5693_MIPI_CTRL00_REG,
+				OV5693_MIPI_CTRL00_CLOCK_LANE_GATE,
+				OV5693_MIPI_CTRL00_CLOCK_LANE_GATE, &ret);
+
 	cci_write(ov5693->regmap, OV5693_SW_STREAM_REG,
 		  enable ? OV5693_START_STREAMING : OV5693_STOP_STREAMING,
 		  &ret);
@@ -1259,6 +1280,9 @@ static int ov5693_check_hwcfg(struct ov5693_device *ov5693)
 		goto out_free_bus_cfg;
 	}
 
+	ov5693->clock_ncont = bus_cfg.bus.mipi_csi2.flags &
+			      V4L2_MBUS_CSI2_NONCONTINUOUS_CLOCK;
+
 out_free_bus_cfg:
 	v4l2_fwnode_endpoint_free(&bus_cfg);
 
-- 
2.43.0