Date:   Sun, 10 Nov 2019 12:16:08 +0000
From:   Jonathan Cameron <jic23@...nel.org>
To:     Gwendal Grignou <gwendal@...omium.org>
Cc:     briannorris@...omium.org, knaack.h@....de, lars@...afoo.de,
        pmeerw@...erw.net, lee.jones@...aro.org, bleung@...omium.org,
        enric.balletbo@...labora.com, dianders@...omium.org,
        groeck@...omium.org, fabien.lahoudere@...labora.com,
        linux-kernel@...r.kernel.org, linux-iio@...r.kernel.org
Subject: Re: [PATCH v4 04/17] platform: chrome: cros-ec: record event
 timestamp in the hard irq

On Tue,  5 Nov 2019 14:26:39 -0800
Gwendal Grignou <gwendal@...omium.org> wrote:

> To improve sensor timestamp precision, given EC and AP are in
> different time domains, the AP needs to try to record the exact
> moment an event was signalled to the AP by the EC as soon as
> possible after it happens.
> 
> First thing in the hard irq is the best place for this.
> 
> Signed-off-by: Gwendal Grignou <gwendal@...omium.org>
A minor issue with kernel-doc (I think...)

Otherwise,
Acked-by: Jonathan Cameron <Jonathan.Cameron@...nel.org>
> ---
> Changes in v4:
>   Check patch with --strict option
>     Alignement
> No changes in v3.
> Changes in v2:
>   Make cros_ec_get_time_ns inline.
>   Using ktime_t instead of s64 when dealing with time.
>   Added code in ishtp to gather timestamp.
> 
>  drivers/platform/chrome/cros_ec.c           | 17 ++++++++++++++---
>  drivers/platform/chrome/cros_ec_ishtp.c     | 17 +++++++++++++++--
>  drivers/platform/chrome/cros_ec_lpc.c       |  2 ++
>  include/linux/platform_data/cros_ec_proto.h | 16 ++++++++++++++++
>  4 files changed, 47 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/platform/chrome/cros_ec.c b/drivers/platform/chrome/cros_ec.c
> index 9b2d07422e17..925f84dbf621 100644
> --- a/drivers/platform/chrome/cros_ec.c
> +++ b/drivers/platform/chrome/cros_ec.c
> @@ -31,6 +31,15 @@ static struct cros_ec_platform pd_p = {
>  	.cmd_offset = EC_CMD_PASSTHRU_OFFSET(CROS_EC_DEV_PD_INDEX),
>  };
>  
> +static irqreturn_t ec_irq_handler(int irq, void *data)
> +{
> +	struct cros_ec_device *ec_dev = data;
> +
> +	ec_dev->last_event_time = cros_ec_get_time_ns();
> +
> +	return IRQ_WAKE_THREAD;
> +}
> +
>  static irqreturn_t ec_irq_thread(int irq, void *data)
>  {
>  	struct cros_ec_device *ec_dev = data;
> @@ -141,9 +150,11 @@ int cros_ec_register(struct cros_ec_device *ec_dev)
>  	}
>  
>  	if (ec_dev->irq) {
> -		err = devm_request_threaded_irq(dev, ec_dev->irq, NULL,
> -				ec_irq_thread, IRQF_TRIGGER_LOW | IRQF_ONESHOT,
> -				"chromeos-ec", ec_dev);
> +		err = devm_request_threaded_irq(dev, ec_dev->irq,
> +						ec_irq_handler,
> +						ec_irq_thread,
> +						IRQF_TRIGGER_LOW | IRQF_ONESHOT,
> +						"chromeos-ec", ec_dev);
>  		if (err) {
>  			dev_err(dev, "Failed to request IRQ %d: %d",
>  				ec_dev->irq, err);
> diff --git a/drivers/platform/chrome/cros_ec_ishtp.c b/drivers/platform/chrome/cros_ec_ishtp.c
> index 25ca2c894b4d..5c848f22b44b 100644
> --- a/drivers/platform/chrome/cros_ec_ishtp.c
> +++ b/drivers/platform/chrome/cros_ec_ishtp.c
> @@ -200,13 +200,14 @@ static int ish_send(struct ishtp_cl_data *client_data,
>   * process_recv() - Received and parse incoming packet
>   * @cros_ish_cl: Client instance to get stats
>   * @rb_in_proc: Host interface message buffer
> + * @timestamp: Timestamp of when parent callback started
>   *
>   * Parse the incoming packet. If it is a response packet then it will
>   * update per instance flags and wake up the caller waiting to for the
>   * response. If it is an event packet then it will schedule event work.
>   */
>  static void process_recv(struct ishtp_cl *cros_ish_cl,
> -			 struct ishtp_cl_rb *rb_in_proc)
> +			 struct ishtp_cl_rb *rb_in_proc, ktime_t timestamp)
>  {
>  	size_t data_len = rb_in_proc->buf_idx;
>  	struct ishtp_cl_data *client_data =
> @@ -295,6 +296,11 @@ static void process_recv(struct ishtp_cl *cros_ish_cl,
>  		break;
>  
>  	case CROS_MKBP_EVENT:
> +		/*
> +		 * Set timestamp from beginning of function since we actually
> +		 * got an incoming MKBP event
> +		 */
> +		client_data->ec_dev->last_event_time = timestamp;
>  		/* The event system doesn't send any data in buffer */
>  		schedule_work(&client_data->work_ec_evt);
>  
> @@ -322,10 +328,17 @@ static void ish_event_cb(struct ishtp_cl_device *cl_device)
>  {
>  	struct ishtp_cl_rb *rb_in_proc;
>  	struct ishtp_cl	*cros_ish_cl = ishtp_get_drvdata(cl_device);
> +	ktime_t timestamp;
> +
> +	/*
> +	 * Take timestamp as close to hardware interrupt as possible for sensor
> +	 * timestamps.
> +	 */
> +	timestamp = cros_ec_get_time_ns();
>  
>  	while ((rb_in_proc = ishtp_cl_rx_get_rb(cros_ish_cl)) != NULL) {
>  		/* Decide what to do with received data */
> -		process_recv(cros_ish_cl, rb_in_proc);
> +		process_recv(cros_ish_cl, rb_in_proc, timestamp);
>  	}
>  }
>  
> diff --git a/drivers/platform/chrome/cros_ec_lpc.c b/drivers/platform/chrome/cros_ec_lpc.c
> index 7d10d909435f..3c77496e164d 100644
> --- a/drivers/platform/chrome/cros_ec_lpc.c
> +++ b/drivers/platform/chrome/cros_ec_lpc.c
> @@ -313,6 +313,8 @@ static void cros_ec_lpc_acpi_notify(acpi_handle device, u32 value, void *data)
>  {
>  	struct cros_ec_device *ec_dev = data;
>  
> +	ec_dev->last_event_time = cros_ec_get_time_ns();
> +
>  	if (ec_dev->mkbp_event_supported &&
>  	    cros_ec_get_next_event(ec_dev, NULL) > 0)
>  		blocking_notifier_call_chain(&ec_dev->event_notifier, 0,
> diff --git a/include/linux/platform_data/cros_ec_proto.h b/include/linux/platform_data/cros_ec_proto.h
> index 691f9e953a96..b183024fef1f 100644
> --- a/include/linux/platform_data/cros_ec_proto.h
> +++ b/include/linux/platform_data/cros_ec_proto.h
> @@ -122,6 +122,8 @@ struct cros_ec_command {
>   * @event_data: Raw payload transferred with the MKBP event.
>   * @event_size: Size in bytes of the event data.
>   * @host_event_wake_mask: Mask of host events that cause wake from suspend.
> + * @last_event_time: exact time from the hard irq when we got notified of
> + *     a new event.
>   * @ec: The platform_device used by the mfd driver to interface with the
>   *      main EC.
>   * @pd: The platform_device used by the mfd driver to interface with the
> @@ -162,6 +164,7 @@ struct cros_ec_device {
>  	int event_size;
>  	u32 host_event_wake_mask;
>  	u32 last_resume_result;
> +	ktime_t last_event_time;
>  
>  	/* The platform devices used by the mfd driver */
>  	struct platform_device *ec;
> @@ -210,4 +213,17 @@ int cros_ec_check_features(struct cros_ec_dev *ec, int feature);
>  
>  int cros_ec_get_sensor_count(struct cros_ec_dev *ec);
>  
> +/**
> + * cros_ec_get_time_ns - Return time in ns.

Fairly sure that's not correct kernel-doc.  Please run
../scripts/kernel-doc over the files and fix the warnings.

 * cros_ec_get_time_ns() - Return time in ns.

> + *
> + * This is the function used to record the time for last_event_time in struct
> + * cros_ec_device during the hard irq.
> + *
> + * Return: ktime_t format since boot.
> + */
> +static inline ktime_t cros_ec_get_time_ns(void)
> +{
> +	return ktime_get_boottime_ns();
> +}
> +
>  #endif /* __LINUX_CROS_EC_PROTO_H */

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