linux-kernel - [PATCH v4 07/15] media: mt9m114: Avoid a reset low spike during probe()

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Message-Id: <20251224-mt9m114-atomisp-v4-7-60b25da7a1bc@oss.qualcomm.com>
Date: Wed, 24 Dec 2025 13:31:16 +0100
From: Hans de Goede <johannes.goede@....qualcomm.com>
To: Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>
Cc: linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Hans de Goede <johannes.goede@....qualcomm.com>
Subject: [PATCH v4 07/15] media: mt9m114: Avoid a reset low spike during
 probe()

mt9m114_probe() requests the reset GPIO in output low state:

	sensor->reset = devm_gpiod_get_optional(dev, "reset", GPIOD_OUT_LOW);

and then almost immediately afterwards calls mt9m114_power_on() which does:

		gpiod_set_value(sensor->reset, 1);
		fsleep(duration);
		gpiod_set_value(sensor->reset, 0);

which means that if the reset pin was high before this code runs that
it will very briefly be driven low because of passing GPIOD_OUT_LOW when
requesting the GPIO only to be driven high again possibly directly after
that. Such a very brief driving low of the reset pin may put the chip in
a confused state.

Request the GPIO in high (reset the chip) state instead to avoid this,
turning the initial gpiod_set_value() in mt9m114_power_on() into a no-op.
and the fsleep() ensures that it will stay high long enough to properly
reset the chip.

Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
Signed-off-by: Hans de Goede <johannes.goede@....qualcomm.com>
---
 drivers/media/i2c/mt9m114.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/media/i2c/mt9m114.c b/drivers/media/i2c/mt9m114.c
index d58445826c090f377db473f7926c1b612874ff78..60afc32acee4df1e7d4f820838b72f6aa3506f8d 100644
--- a/drivers/media/i2c/mt9m114.c
+++ b/drivers/media/i2c/mt9m114.c
@@ -2455,7 +2455,7 @@ static int mt9m114_probe(struct i2c_client *client)
 		goto error_ep_free;
 	}
 
-	sensor->reset = devm_gpiod_get_optional(dev, "reset", GPIOD_OUT_LOW);
+	sensor->reset = devm_gpiod_get_optional(dev, "reset", GPIOD_OUT_HIGH);
 	if (IS_ERR(sensor->reset)) {
 		ret = PTR_ERR(sensor->reset);
 		dev_err_probe(dev, ret, "Failed to get reset GPIO\n");

-- 
2.52.0