[PATCH RFC 1/4] media: imx8mq-mipi-csi2: Make reset release SoC-specific

[Vincent Cloutier]

From: Vincent Cloutier <vincent@xxxxxxxxxxx>

The CSI-2 software reset helper currently asserts the reset control and
then releases it again unconditionally.

That release step is required by the i.MX8QXP path, but it changes the
reset sequence used by i.MX8MQ. On Librem 5r4, which is i.MX8MQ-based,
the unconditional release step prevents the camera pipeline from producing
frames after reset; captures time out waiting for EOF from the CSI bridge.

This series enables the Librem 5 rear camera on the second i.MX8MQ CSI-2
receiver. Keep the i.MX8MQ path on the known-working assert-only software
reset sequence while preserving the explicit release step for i.MX8QXP.

Make reset release opt-in through platform data.

Tested on Librem 5r4 with the existing HI846 front camera and the S5K3L6
rear camera added by this series.

Signed-off-by: Vincent Cloutier <vincent@xxxxxxxxxxx>
Assisted-by: OpenCode:gpt-5.5
---
 drivers/media/platform/nxp/imx8mq-mipi-csi2.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/drivers/media/platform/nxp/imx8mq-mipi-csi2.c b/drivers/media/platform/nxp/imx8mq-mipi-csi2.c
index 950793297496..xxxxxxxxxxxx 100644
--- a/drivers/media/platform/nxp/imx8mq-mipi-csi2.c
+++ b/drivers/media/platform/nxp/imx8mq-mipi-csi2.c
@@ -76,6 +76,7 @@ struct imx8mq_plat_data {
 	int (*enable)(struct csi_state *state, u32 hs_settle);
 	void (*disable)(struct csi_state *state);
 	bool use_reg_csr;
+	bool needs_reset_deassert;
 };
 
 /*
@@ -244,6 +245,7 @@ static const struct imx8mq_plat_data imx8qxp_data = {
 	.enable = imx8qxp_gpr_enable,
 	.disable = imx8qxp_gpr_disable,
 	.use_reg_csr = true,
+	.needs_reset_deassert = true,
 };
 
 static const struct csi2_pix_format imx8mq_mipi_csi_formats[] = {
@@ -363,8 +365,12 @@ static int imx8mq_mipi_csi_sw_reset(struct csi_state *state)
 		return ret;
 	}
 
-	/* Explicitly release reset to make sure reset bits are cleared. */
-	return reset_control_deassert(state->rst);
+	/*
+	 * Some SoC integrations require an explicit release after reset
+	 * assertion. Keep this SoC-specific so i.MX8MQ retains its
+	 * known-working assert-only sequence.
+	 */
+	if (!state->pdata->needs_reset_deassert)
+		return 0;
+
+	return reset_control_deassert(state->rst);
 }
 
 static void imx8mq_mipi_csi_set_params(struct csi_state *state)
-- 
2.53.0