The MT9P006 sensor driver sporadically fails to probe because the sensor responds with a NACK condition to I2C address on the bus during an attempt to read the sensor MT9P031_CHIP_VERSION register in mt9p031_registered(). Neither the MT9P006 nor MT9P031 datasheets are clear on reset signal timing. Older MT9M034 [1] datasheet provides those timing figures in Appendix-A and indicates it is necessary to wait 850000 EXTCLK cycles before starting any I2C communication. Add such a delay, which does make the sporadic I2C NACK go away, so it is likely similar constraint applies to this sensor. [1] https://www.onsemi.com/pdf/datasheet/mt9m034-d.pdf Signed-off-by: Marek Vasut <marex@xxxxxxx> --- Cc: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> Cc: Mauro Carvalho Chehab <mchehab+huawei@xxxxxxxxxx> Cc: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx> Cc: Stefan Riedmueller <s.riedmueller@xxxxxxxxx> --- V2: - In case clk_get_rate() returns 0, use slowest supported clock to avoid division by zero --- drivers/media/i2c/mt9p031.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/drivers/media/i2c/mt9p031.c b/drivers/media/i2c/mt9p031.c index 45f7b5e52bc39..5f5caafe56887 100644 --- a/drivers/media/i2c/mt9p031.c +++ b/drivers/media/i2c/mt9p031.c @@ -307,6 +307,7 @@ static inline int mt9p031_pll_disable(struct mt9p031 *mt9p031) static int mt9p031_power_on(struct mt9p031 *mt9p031) { + unsigned long rate, delay; int ret; /* Ensure RESET_BAR is active */ @@ -334,7 +335,12 @@ static int mt9p031_power_on(struct mt9p031 *mt9p031) /* Now RESET_BAR must be high */ if (mt9p031->reset) { gpiod_set_value(mt9p031->reset, 0); - usleep_range(1000, 2000); + /* Wait 850000 EXTCLK cycles before de-asserting reset. */ + rate = clk_get_rate(mt9p031->clk); + if (!rate) + rate = 6000000; /* Slowest supported clock, 6 MHz */ + delay = DIV_ROUND_UP(850000 * 1000, rate); + msleep(delay); } return 0; -- 2.35.1
