Hello Laurent,

On 01/06/2016 07:59 AM, Laurent Pinchart wrote:

Hi Javier,

Thankk you for the patch.

Thanks a lot for your feedback.
 

On Monday 04 January 2016 09:25:31 Javier Martinez Canillas wrote:

quoted

After power-up, the tvp5150 decoder is in a unknown state until the
RESETB pin is driven LOW which reset all the registers and restarts
the chip's internal state machine.

The init sequence has some timing constraints and the RESETB signal
can only be used if the PDN (Power-down) pin is first released.

So, the initialization sequence is as follows:

1- PDN (active-low) is driven HIGH so the chip is power-up
2- A 20 ms delay is needed before sending a RESETB (active-low) signal.
3- The RESETB pulse duration is 500 ns.
4- A 200 us delay is needed for the I2C client to be active after reset.

This patch used as a reference the logic in the IGEPv2 board file from
the ISEE 2.6.37 vendor tree.

Signed-off-by: Javier Martinez Canillas <redacted>
---

 drivers/media/i2c/tvp5150.c | 35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/drivers/media/i2c/tvp5150.c b/drivers/media/i2c/tvp5150.c
index caac96a577f8..fed89a811ab7 100644
--- a/drivers/media/i2c/tvp5150.c
+++ b/drivers/media/i2c/tvp5150.c

@@ -5,6 +5,7 @@
  * This code is placed under the terms of the GNU General Public License v2

*/

+#include <linux/of_gpio.h>

Let's keep the headers sorted alphabetically if you don't mind :-)

Right, sorry about that.
 

quoted

 #include <linux/i2c.h>
 #include <linux/slab.h>
 #include <linux/videodev2.h>

@@ -1197,6 +1198,36 @@ static int tvp5150_detect_version(struct tvp5150

*core) return 0;
 }

+static inline int tvp5150_init(struct i2c_client *c)
+{
+	struct gpio_desc *pdn_gpio;
+	struct gpio_desc *reset_gpio;
+
+	pdn_gpio = devm_gpiod_get_optional(&c->dev, "powerdown", GPIOD_OUT_HIGH);
+	if (IS_ERR(pdn_gpio))
+		return PTR_ERR(pdn_gpio);
+
+	if (pdn_gpio) {
+		gpiod_set_value_cansleep(pdn_gpio, 0);
+		/* Delay time between power supplies active and reset */
+		msleep(20);

How about usleep_range() instead ?

Documentation/timers/timers-howto.txt says that usleep_range() should be
used for 1ms - 20ms and msleep() for 20ms+ so since this was a boundary
value, I chose for msleep() but I can use usleep_range() if you want.

I've no strong opinion on this.

quoted

+	}
+
+	reset_gpio = devm_gpiod_get_optional(&c->dev, "reset", GPIOD_OUT_HIGH);
+	if (IS_ERR(reset_gpio))
+		return PTR_ERR(reset_gpio);
+
+	if (reset_gpio) {
+		/* RESETB pulse duration */
+		ndelay(500);

Is the timing so sensitive that we need a delay, or could we use 
usleep_range() ?

According to my tests, it is a minimum value but I chose to do a delay since
the time is very short and also Documentation/timers/timers-howto.txt says
that using usleep for very short periods may not be worth it due the overhead
of setting up the hrtimers for usleep.

Best regards,
-- 
Javier Martinez Canillas
Open Source Group
Samsung Research America
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