Re: [PATCH 2/5] gnss: sirf: power on logic for devices without wakeup signal

[H. Nikolaus Schaller]

> Am 18.11.2018 um 22:57 schrieb Andreas Kemnade <andreas@xxxxxxxxxxxx>:
> 
> Some Wi2Wi devices do not have a wakeup output, so device state can
> only be indirectly detected by looking whether there is communitcation
> over the serial lines.
> Additionally it checks for the initial state of the device during
> probing to ensure it is off.
> Timeout values need to be increased, because the reaction on serial line
> is slower and are in line  with previous patches by
> Neil Brown <neilb@xxxxxxx> and  H. Nikolaus Schaller <hns@xxxxxxxxxxxxx>.
> 
> Signed-off-by: Andreas Kemnade <andreas@xxxxxxxxxxxx>
> ---
> drivers/gnss/sirf.c | 97 +++++++++++++++++++++++++++++++++++------------------
> 1 file changed, 65 insertions(+), 32 deletions(-)
> 
> diff --git a/drivers/gnss/sirf.c b/drivers/gnss/sirf.c
> index b5efbb062316..6a0e5c0a2d62 100644
> --- a/drivers/gnss/sirf.c
> +++ b/drivers/gnss/sirf.c
> @@ -22,8 +22,8 @@
> 
> #define SIRF_BOOT_DELAY			500
> #define SIRF_ON_OFF_PULSE_TIME		100
> -#define SIRF_ACTIVATE_TIMEOUT		200
> -#define SIRF_HIBERNATE_TIMEOUT		200
> +#define SIRF_ACTIVATE_TIMEOUT		1000
> +#define SIRF_HIBERNATE_TIMEOUT		1000
> 
> struct sirf_data {
> 	struct gnss_device *gdev;
> @@ -45,26 +45,14 @@ static int sirf_open(struct gnss_device *gdev)
> 	int ret;
> 
> 	data->opened = true;
> -	ret = serdev_device_open(serdev);
> -	if (ret)
> -		return ret;
> -
> -	serdev_device_set_baudrate(serdev, data->speed);
> -	serdev_device_set_flow_control(serdev, false);
> 
> 	ret = pm_runtime_get_sync(&serdev->dev);
> 	if (ret < 0) {
> 		dev_err(&gdev->dev, "failed to runtime resume: %d\n", ret);
> 		pm_runtime_put_noidle(&serdev->dev);
> 		data->opened = false;
> -		goto err_close;
> 	}
> 
> -	return 0;
> -
> -err_close:
> -	serdev_device_close(serdev);
> -
> 	return ret;
> }
> 
> @@ -73,8 +61,6 @@ static void sirf_close(struct gnss_device *gdev)
> 	struct sirf_data *data = gnss_get_drvdata(gdev);
> 	struct serdev_device *serdev = data->serdev;
> 
> -	serdev_device_close(serdev);
> -
> 	pm_runtime_put(&serdev->dev);
> 	data->opened = false;
> }
> @@ -109,6 +95,11 @@ static int sirf_receive_buf(struct serdev_device *serdev,
> 	struct sirf_data *data = serdev_device_get_drvdata(serdev);
> 	struct gnss_device *gdev = data->gdev;
> 
> +	if ((!data->wakeup) && (!data->active)) {
> +		data->active = 1;
> +		wake_up_interruptible(&data->power_wait);
> +	}
> +
> 	/*
> 	 * we might come here everytime when runtime is resumed
> 	 * and data is received. Two cases are possible
> @@ -149,6 +140,25 @@ static int sirf_wait_for_power_state(struct sirf_data *data, bool active,
> {
> 	int ret;
> 
> +	/* no wakeup pin, success condition is that
> +	 * no byte comes in in the period
> +	 */
> +	if ((!data->wakeup) && (!active) && (data->active)) {
> +		/* some bytes might come, so sleep a bit first */
> +		msleep(timeout);
> +		data->active = false;
> +		ret = wait_event_interruptible_timeout(data->power_wait,
> +			data->active == true, msecs_to_jiffies(timeout));
> +
> +		if (ret < 0)
> +			return ret;
> +
> +		/* we are still getting woken up -> timeout */
> +		if (ret > 0)
> +			return -ETIMEDOUT;
> +		return 0;
> +	}
> +
> 	ret = wait_event_interruptible_timeout(data->power_wait,
> 			data->active == active, msecs_to_jiffies(timeout));
> 	if (ret < 0)
> @@ -203,21 +213,48 @@ static int sirf_set_active(struct sirf_data *data, bool active)
> static int sirf_runtime_suspend(struct device *dev)
> {
> 	struct sirf_data *data = dev_get_drvdata(dev);
> +	int ret;
> 
> 	if (!data->on_off)
> 		return regulator_disable(data->vcc);
> +	ret = sirf_set_active(data, false);
> 
> -	return sirf_set_active(data, false);
> +	if (ret)
> +		dev_err(dev, "failed to deactivate");
> +
> +	/* we should close it anyways, so the following receptions
> +	 * will not run into the empty
> +	 */
> +	serdev_device_close(data->serdev);
> +	return 0;
> }
> 
> static int sirf_runtime_resume(struct device *dev)
> {
> +	int ret;
> 	struct sirf_data *data = dev_get_drvdata(dev);
> +	ret = serdev_device_open(data->serdev);
> +	if (ret)
> +		return ret;
> 
> -	if (!data->on_off)
> -		return regulator_enable(data->vcc);
> +	serdev_device_set_baudrate(data->serdev, data->speed);
> +	serdev_device_set_flow_control(data->serdev, false);
> +
> +	if (!data->on_off) {
> +		ret = regulator_enable(data->vcc);
> +		if (ret)
> +			goto err_close_serdev;
> +	}
> +	ret = sirf_set_active(data, true);
> +
> +	if (!ret)
> +		return 0;
> 
> -	return sirf_set_active(data, true);
> +	if (!data->on_off)
> +		regulator_disable(data->vcc);
> +err_close_serdev:
> +	serdev_device_close(data->serdev);
> +	return ret;
> }
> 
> static int __maybe_unused sirf_suspend(struct device *dev)
> @@ -311,18 +348,6 @@ static int sirf_probe(struct serdev_device *serdev)
> 	if (data->on_off) {
> 		data->wakeup = devm_gpiod_get_optional(dev, "sirf,wakeup",
> 				GPIOD_IN);
> -		if (IS_ERR(data->wakeup))
> -			goto err_put_device;
> -
> -		/*
> -		 * Configurations where WAKEUP has been left not connected,
> -		 * are currently not supported.
> -		 */
> -		if (!data->wakeup) {
> -			dev_err(dev, "no wakeup gpio specified\n");
> -			ret = -ENODEV;
> -			goto err_put_device;
> -		}
> 	}
> 
> 	if (data->wakeup) {
> @@ -352,6 +377,13 @@ static int sirf_probe(struct serdev_device *serdev)
> 	if (IS_ENABLED(CONFIG_PM)) {
> 		pm_runtime_set_suspended(dev);	/* clear runtime_error flag */
> 		pm_runtime_enable(dev);
> +		/* device might be enabled at boot, so lets first enable it,
> +		 * then disable it to bring it into a clear state
> +		 */

That is an interesting trick to solve the "device is powered on but kernel does
not know" problem.

The assumption to make your trick work is that there is nobody besides the
running kernel who can turn on/off the device so that after this operation,
the kernel can simply track the power state in a boolean flag.

Since the power control gpio is grabbed by this driver, it can't be exported
to user-space and hence I think we can take this assumption for granted.

> +		ret = pm_runtime_get_sync(dev);
> +		if (ret)
> +			goto err_disable_rpm;
> +		pm_runtime_put(dev);
> 	} else {
> 		ret = sirf_runtime_resume(dev);
> 		if (ret < 0)
> @@ -401,6 +433,7 @@ static const struct of_device_id sirf_of_match[] = {
> 	{ .compatible = "linx,r4" },
> 	{ .compatible = "wi2wi,w2sg0008i" },
> 	{ .compatible = "wi2wi,w2sg0084i" },
> +	{ .compatible = "wi2wi,w2sg0004" },
> 	{},
> };
> MODULE_DEVICE_TABLE(of, sirf_of_match);
> -- 
> 2.11.0
> 
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BR,
Nikolaus