linux-kernel - [PATCH v2] media: i2c: imx412: wait for NVM read (T7) before programming mode registers

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Message-Id: <20260109044913.3310-1-wenmeng.liu@oss.qualcomm.com>
Date: Fri,  9 Jan 2026 12:49:13 +0800
From: Wenmeng Liu <wenmeng.liu@....qualcomm.com>
To: sakari.ailus@...ux.intel.com, mchehab@...nel.org
Cc: linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        wenmeng.liu@....qualcomm.com
Subject: [PATCH v2] media: i2c: imx412: wait for NVM read (T7) before programming mode registers

During sensor bring-up, the IMX412 performs CCI ID read (T6 ~0.6 ms) and
parameter loading from NVM (T7 ≤ 8 ms) after INCK/XCLR rise. Writing the
mode register list while T7 is in progress can cause  failed
register programming.

Move the usleep_range(7400, 8000) to the beginning of
imx412_start_streaming(), so the driver waits for the NVM read window (T7)
to complete before pushing the mode registers and sending the streaming
command (T8). This change preserves the original delay length but fixes
the ordering to match the datasheet timing:

- T6: CCI ID read wait (~0.6 ms)
- T7: NVM parameter read (≤ 8 ms) — now fully elapsed before any
      register writes
- T8: start of first streaming after issuing MODE_SELECT

Signed-off-by: Wenmeng Liu <wenmeng.liu@....qualcomm.com>
---
Changes in v2:
- Move the 7.4–8 ms delay before mode-register programming to satisfy T7 (NVM read).
- Link to v1: https://lore.kernel.org/all/20251222-imx412-v1-1-51c7e724b376@oss.qualcomm.com/
---
 drivers/media/i2c/imx412.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/media/i2c/imx412.c b/drivers/media/i2c/imx412.c
index b3826f803547..ed249a95ff35 100644
--- a/drivers/media/i2c/imx412.c
+++ b/drivers/media/i2c/imx412.c
@@ -798,6 +798,9 @@ static int imx412_start_streaming(struct imx412 *imx412)
 	const struct imx412_reg_list *reg_list;
 	int ret;
 
+	/* Wait T7 (≤8ms) so NVM read finishes; avoid I2C NACK when writing mode regs */
+	usleep_range(7400, 8000);
+
 	/* Write sensor mode registers */
 	reg_list = &imx412->cur_mode->reg_list;
 	ret = imx412_write_regs(imx412, reg_list->regs,
@@ -814,9 +817,6 @@ static int imx412_start_streaming(struct imx412 *imx412)
 		return ret;
 	}
 
-	/* Delay is required before streaming*/
-	usleep_range(7400, 8000);
-
 	/* Start streaming */
 	ret = imx412_write_reg(imx412, IMX412_REG_MODE_SELECT,
 			       1, IMX412_MODE_STREAMING);
-- 
2.34.1