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Date: Tue, 22 Jan 2019 18:56:43 +0100
From: Johan Hovold <johan@...nel.org>
To: Andreas Kemnade <andreas@...nade.info>
Cc: letux-kernel@...nphoenux.org, johan@...nel.org, robh+dt@...nel.org,
mark.rutland@....com, devicetree@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 3/6] gnss: sirf: add support for configurations
without wakeup signal
On Wed, Jan 16, 2019 at 10:18:09PM +0100, Andreas Kemnade wrote:
> Some Wi2Wi devices do not have a wakeup output, so device state can
> only be indirectly detected by looking whether there is communitcation
communication
> over the serial lines.
> This approach requires a report cycle set to a low value to be reliable.
How low? Better to spell out your current assumptions so people can
configure accordingly.
> Signed-off-by: Andreas Kemnade <andreas@...nade.info>
> ---
> Changes in v3:
> - was 2/5 earlier
> - changed commit headline
> - more style cleanup
> - split out initial power off as 2/6
> - introduced SIRF_REPORT_CYCLE constant
> - added documentation about limitations
> - ignore first data after power state on so no
> shutdown meassages are treated as power on success
> - clearer logic in sirf_wait_for_power_state
>
> Changes in v2:
> - style cleanup
> - do not keep serdev open just because runtime is active,
> only when needed (gnss device is opened or state is changed)
> - clearer timeout semantics
>
>
> drivers/gnss/sirf.c | 117 +++++++++++++++++++++++++++++++++++++++++-----------
> 1 file changed, 93 insertions(+), 24 deletions(-)
>
> diff --git a/drivers/gnss/sirf.c b/drivers/gnss/sirf.c
> index c7706b91f6f0..943a2ec9b708 100644
> --- a/drivers/gnss/sirf.c
> +++ b/drivers/gnss/sirf.c
> @@ -25,6 +25,16 @@
> #define SIRF_ON_OFF_PULSE_TIME 100
> #define SIRF_ACTIVATE_TIMEOUT 200
> #define SIRF_HIBERNATE_TIMEOUT 200
> +/*
> + * If no data arrives for this time, we expect the chip to be off.
"we assume that the chip is off"?
> + * REVISIT: The report cycle is configurable and can be several minutes long,
> + * so this will only work reliably if the report cycle is set to a reasonable
> + * low value. Also power saving settings (like send data only on movement)
> + * might things work even worse.
> + * Workaround might be to parse shutdown or bootup messages.
> + * This problem mainly makes error checking uncertain.
I'd drop the last sentence. You could also fail to detect the state and
waste power indefinitely, right?
> + */
> +#define SIRF_REPORT_CYCLE 2000
>
> struct sirf_data {
> struct gnss_device *gdev;
> @@ -39,9 +49,45 @@ struct sirf_data {
> struct mutex gdev_mutex;
> bool open;
>
> + /*
> + * Using the same mutex inside a serdev callback
> + * and around a serdev call leads to lockdep problems.
Lockdep is not a problem; a possible deadlock is. Just drop this comment.
> + */
> + struct mutex serdev_mutex;
> + int serdev_count;
> +
> wait_queue_head_t power_wait;
> };
>
> +static int sirf_serdev_open(struct sirf_data *data)
> +{
> + int ret = 0;
> +
> + mutex_lock(&data->serdev_mutex);
> + if (++data->serdev_count == 1) {
> + ret = serdev_device_open(data->serdev);
> + if (ret) {
> + data->serdev_count--;
> + mutex_unlock(&data->serdev_mutex);
Use a common "out_unlock:" path below.
> + return ret;
> + }
> +
> + serdev_device_set_baudrate(data->serdev, data->speed);
> + serdev_device_set_flow_control(data->serdev, false);
> + }
> + mutex_unlock(&data->serdev_mutex);
> +
> + return ret;
> +}
> @@ -128,6 +170,11 @@ static int sirf_receive_buf(struct serdev_device *serdev,
> struct gnss_device *gdev = data->gdev;
> int ret = 0;
>
> + if (!data->wakeup && !data->active) {
> + data->active = true;
> + wake_up_interruptible(&data->power_wait);
> + }
> +
> mutex_lock(&data->gdev_mutex);
> if (data->open)
> ret = gnss_insert_raw(gdev, buf, count);
> @@ -163,6 +210,24 @@ static int sirf_wait_for_power_state(struct sirf_data *data, bool active,
> {
> int ret;
>
> + if (!data->wakeup) {
You currently don't share any code with the wakeup-case; better to keep
this in a separate helper if so.
> + /* Wait for boot or shutdown messages */
/* Wait for state change (including any shutdown messages). */
> + msleep(timeout);
> + data->active = false;
> + /* Now check if it is really off. */
You now also use this code to check for activate state:
/* Wait for data reception or timeout. */
> + ret = wait_event_interruptible_timeout(data->power_wait,
> + data->active,
> + msecs_to_jiffies(SIRF_REPORT_CYCLE));
> + if (ret < 0)
> + return ret;
> +
> + if ((ret > 0 && !active) ||
> + (ret == 0 && active))
Split these cases in two add add comments (failed suspend and failed
resume) for readability.
> + return -ETIMEDOUT;
> +
> + return 0;
> + }
> +
> ret = wait_event_interruptible_timeout(data->power_wait,
> data->active == active, msecs_to_jiffies(timeout));
> if (ret < 0)
> @@ -195,18 +260,29 @@ static int sirf_set_active(struct sirf_data *data, bool active)
> else
> timeout = SIRF_HIBERNATE_TIMEOUT;
>
> + if (!data->wakeup) {
> + ret = sirf_serdev_open(data);
> + if (ret)
> + return ret;
> + }
> +
> do {
> - sirf_pulse_on_off(data);
> + /*
> + * Try to avoid unneeded, time-consuming state toggles
> + * in the configurations without wakeup signal. This counts
> + * especially for the initial off state check.
> + */
> + if (data->wakeup || data->active || active)
> + sirf_pulse_on_off(data);
Special casing like this only hurts readability. This is better handled
as a I did for the wakeup case in the series I just posted, that is, by
making sure the receiver is hibernated in probe. You just need to add a
helper to determine the state for no-wakeup.
> +
> ret = sirf_wait_for_power_state(data, active, timeout);
> - if (ret < 0) {
> - if (ret == -ETIMEDOUT)
> - continue;
> + } while (ret == -ETIMEDOUT && retries--);
Why change this?
>
> - return ret;
A break should do right?
> - }
> + if (!data->wakeup)
> + sirf_serdev_close(data);
>
> - break;
> - } while (retries--);
> + if (ret)
> + return ret;
>
> if (retries < 0)
> return -ETIMEDOUT;
Johan
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