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Date: Tue, 27 Jun 2023 16:27:59 +0200
From: Rodolfo Giometti <giometti@...eenne.com>
To: Eliav Farber <farbere@...zon.com>, robh+dt@...nel.org,
krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org,
devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: ronenk@...zon.com, talel@...zon.com, hhhawa@...zon.com,
jonnyc@...zon.com, itamark@...zon.com, shellykz@...zon.com,
amitlavi@...zon.com, almogbs@...zon.com
Subject: Re: [PATCH 1/5] pps: add pulse-width calculation in nsec
On 25/06/23 16:21, Eliav Farber wrote:
> This change adds PPS pulse-width calculation in nano seconds.
> Width time can be calculated for both assert time and reset time.
>
> Calculation can be done only if capture ASSERT and capture CLEAR modes
> are both enabled.
>
> Assert width is calculated as:
> clear-time - assert-time
> and clear width is calculated as:
> assert-time - clear-time
>
> Read-only sysfs were added to get the last pulse-width time and event
> sequence.
> Examples:
> * cat /sys/class/pps/pps0/pulse_width_assert
> 20001450#85
> * cat /sys/class/pps/pps1/pulse_width_clear
> 979893314#16
>
> Signed-off-by: Eliav Farber <farbere@...zon.com>
> ---
> drivers/pps/kapi.c | 49 ++++++++++++++++++++++++++++++++++++++
> drivers/pps/pps.c | 9 +++++++
> drivers/pps/sysfs.c | 30 +++++++++++++++++++++++
> include/linux/pps_kernel.h | 3 +++
> include/uapi/linux/pps.h | 19 +++++++++++++++
> 5 files changed, 110 insertions(+)
>
> diff --git a/drivers/pps/kapi.c b/drivers/pps/kapi.c
> index d9d566f70ed1..deeecfc0a3ee 100644
> --- a/drivers/pps/kapi.c
> +++ b/drivers/pps/kapi.c
> @@ -82,6 +82,14 @@ struct pps_device *pps_register_source(struct pps_source_info *info,
> goto pps_register_source_exit;
> }
>
> + if ((info->mode & PPS_WIDTHBOTH) &&
> + ((info->mode & PPS_CAPTUREBOTH) != PPS_CAPTUREBOTH)) {
> + pr_err("%s: width can't be calculated without both captures (mode = 0x%x)\n",
> + info->name, info->mode);
> + err = -EINVAL;
> + goto pps_register_source_exit;
> + }
See the comment below where you define PPS_WIDTHBOTH.
> /* Allocate memory for the new PPS source struct */
> pps = kzalloc(sizeof(struct pps_device), GFP_KERNEL);
> if (pps == NULL) {
> @@ -143,6 +151,39 @@ void pps_unregister_source(struct pps_device *pps)
> }
> EXPORT_SYMBOL(pps_unregister_source);
>
> +static u64 pps_ktime_sub(struct pps_ktime *ts1, struct pps_ktime *ts2)
> +{
> + if (ts1->sec == ts2->sec)
> + return (ts1->nsec > ts2->nsec) ? (ts1->nsec - ts2->nsec) : (ts2->nsec - ts1->nsec);
> +
> + if (ts1->sec > ts2->sec)
> + return (ts1->sec - ts2->sec) * NSEC_PER_SEC + ts1->nsec - ts2->nsec;
> +
> + return (ts2->sec - ts1->sec) * NSEC_PER_SEC + ts2->nsec - ts1->nsec;
> +}
> +
> +static void pps_calc_clear_width(struct pps_device *pps)
> +{
> + if (pps->clear_sequence == 0)
> + return;
> +
> + pps->clear_width.sequence++;
I don't understand the meaning of this field... regarding assert and clear it
states the n-th sample but in this case...? Why do you need it?
> + pps->clear_width.nsec = pps_ktime_sub(&pps->assert_tu, &pps->clear_tu);
> + dev_dbg(pps->dev, "PPS clear width = %llu#%u\n",
> + pps->clear_width.nsec, pps->clear_width.sequence);
> +}
> +
> +static void pps_calc_assert_width(struct pps_device *pps)
> +{
> + if (pps->assert_sequence == 0)
> + return;
> +
> + pps->assert_width.sequence++;
Ditto.
> + pps->assert_width.nsec = pps_ktime_sub(&pps->clear_tu, &pps->assert_tu);
> + dev_dbg(pps->dev, "PPS assert width = %llu#%u\n",
> + pps->assert_width.nsec, pps->assert_width.sequence);
> +}
> +
> /* pps_event - register a PPS event into the system
> * @pps: the PPS device
> * @ts: the event timestamp
> @@ -191,6 +232,10 @@ void pps_event(struct pps_device *pps, struct pps_event_time *ts, int event,
> dev_dbg(pps->dev, "capture assert seq #%u\n",
> pps->assert_sequence);
>
> + /* Calculate clear pulse-width */
> + if (pps->params.mode & PPS_WIDTHCLEAR)
> + pps_calc_clear_width(pps);
> +
> captured = ~0;
> }
> if (event & pps->params.mode & PPS_CAPTURECLEAR) {
> @@ -205,6 +250,10 @@ void pps_event(struct pps_device *pps, struct pps_event_time *ts, int event,
> dev_dbg(pps->dev, "capture clear seq #%u\n",
> pps->clear_sequence);
>
> + /* Calculate assert pulse-width */
> + if (pps->params.mode & PPS_WIDTHASSERT)
> + pps_calc_assert_width(pps);
> +
> captured = ~0;
> }
>
> diff --git a/drivers/pps/pps.c b/drivers/pps/pps.c
> index 5d19baae6a38..8299a272af11 100644
> --- a/drivers/pps/pps.c
> +++ b/drivers/pps/pps.c
> @@ -195,6 +195,11 @@ static long pps_cdev_ioctl(struct file *file,
> fdata.info.clear_tu = pps->clear_tu;
> fdata.info.current_mode = pps->current_mode;
>
> + memcpy(&fdata.info.assert_width, &pps->assert_width,
> + sizeof(struct pps_kwidth));
> + memcpy(&fdata.info.clear_width, &pps->clear_width,
> + sizeof(struct pps_kwidth));
> +
> spin_unlock_irq(&pps->lock);
>
> err = copy_to_user(uarg, &fdata, sizeof(struct pps_fdata));
> @@ -283,6 +288,10 @@ static long pps_cdev_compat_ioctl(struct file *file,
> sizeof(struct pps_ktime_compat));
> memcpy(&compat.info.clear_tu, &pps->clear_tu,
> sizeof(struct pps_ktime_compat));
> + memcpy(&compat.info.assert_width, &pps->assert_width,
> + sizeof(struct pps_kwidth_compat));
> + memcpy(&compat.info.clear_width, &pps->clear_width,
> + sizeof(struct pps_kwidth_compat));
>
> spin_unlock_irq(&pps->lock);
>
> diff --git a/drivers/pps/sysfs.c b/drivers/pps/sysfs.c
> index 134bc33f6ad0..3e34de77dba6 100644
> --- a/drivers/pps/sysfs.c
> +++ b/drivers/pps/sysfs.c
> @@ -79,6 +79,34 @@ static ssize_t path_show(struct device *dev, struct device_attribute *attr,
> }
> static DEVICE_ATTR_RO(path);
>
> +static ssize_t pulse_width_assert_show(struct device *dev,
> + struct device_attribute *attr,
> + char *buf)
> +{
> + struct pps_device *pps = dev_get_drvdata(dev);
> +
> + if (!(pps->info.mode & PPS_WIDTHASSERT))
> + return 0;
> +
> + return sprintf(buf, "%llu#%u\n",
> + pps->assert_width.nsec, pps->assert_width.sequence);
> +}
> +static DEVICE_ATTR_RO(pulse_width_assert);
> +
> +static ssize_t pulse_width_clear_show(struct device *dev,
> + struct device_attribute *attr,
> + char *buf)
> +{
> + struct pps_device *pps = dev_get_drvdata(dev);
> +
> + if (!(pps->info.mode & PPS_WIDTHCLEAR))
> + return 0;
> +
> + return sprintf(buf, "%llu#%u\n",
> + pps->clear_width.nsec, pps->clear_width.sequence);
> +}
> +static DEVICE_ATTR_RO(pulse_width_clear);
> +
> static struct attribute *pps_attrs[] = {
> &dev_attr_assert.attr,
> &dev_attr_clear.attr,
> @@ -86,6 +114,8 @@ static struct attribute *pps_attrs[] = {
> &dev_attr_echo.attr,
> &dev_attr_name.attr,
> &dev_attr_path.attr,
> + &dev_attr_pulse_width_assert.attr,
> + &dev_attr_pulse_width_clear.attr,
> NULL,
> };
>
> diff --git a/include/linux/pps_kernel.h b/include/linux/pps_kernel.h
> index 78c8ac4951b5..15f2338095c6 100644
> --- a/include/linux/pps_kernel.h
> +++ b/include/linux/pps_kernel.h
> @@ -51,6 +51,9 @@ struct pps_device {
> struct pps_ktime clear_tu;
> int current_mode; /* PPS mode at event time */
>
> + struct pps_kwidth assert_width; /* PPS assert pulse-width time and event seq # */
> + struct pps_kwidth clear_width; /* PPS clear pulse-width time and event seq # */
> +
> unsigned int last_ev; /* last PPS event id */
> wait_queue_head_t queue; /* PPS event queue */
>
> diff --git a/include/uapi/linux/pps.h b/include/uapi/linux/pps.h
> index 009ebcd8ced5..dd93dac0afc1 100644
> --- a/include/uapi/linux/pps.h
> +++ b/include/uapi/linux/pps.h
> @@ -64,12 +64,24 @@ struct pps_ktime_compat {
> } __attribute__((packed, aligned(4)));
> #define PPS_TIME_INVALID (1<<0) /* used to specify timeout==NULL */
>
> +struct pps_kwidth {
> + __u64 nsec;
> + __u32 sequence;
> +};
> +
> +struct pps_kwidth_compat {
> + __u64 nsec;
> + __u32 sequence;
> +} __attribute__((packed, aligned(4)));
Why do you need a new type? Since both assert_width and clear_width are time
quantities as far as assert_tu and clear_tu, they can be of the same type, can't
they? Or, at least they can simply be __u64 since having an assert_width or
clear_width longer than 1 second is a non-sense...
> struct pps_kinfo {
> __u32 assert_sequence; /* seq. num. of assert event */
> __u32 clear_sequence; /* seq. num. of clear event */
> struct pps_ktime assert_tu; /* time of assert event */
> struct pps_ktime clear_tu; /* time of clear event */
> int current_mode; /* current mode bits */
> + struct pps_kwidth assert_width; /* assert pulse-width time and seq. num. */
> + struct pps_kwidth clear_width; /* clear pulse-width time and seq. num. */
> };
Altering this structure may break userspace code... also rfc2783 at section-3.2
states that:
The API defines these new data structures:
typedef struct {
pps_seq_t assert_sequence; /* assert event seq # */
pps_seq_t clear_sequence; /* clear event seq # */
pps_timeu_t assert_tu;
pps_timeu_t clear_tu;
int current_mode; /* current mode bits */
} pps_info_t;
So, I'm not willing to change this structure just to add this new data that I
don't even know where it's used...
If you just read these information via sysfs, please drop these part.
> struct pps_kinfo_compat {
> @@ -78,6 +90,8 @@ struct pps_kinfo_compat {
> struct pps_ktime_compat assert_tu; /* time of assert event */
> struct pps_ktime_compat clear_tu; /* time of clear event */
> int current_mode; /* current mode bits */
> + struct pps_kwidth_compat assert_width; /* assert pulse-width time and seq. num. */
> + struct pps_kwidth_compat clear_width; /* clear pulse-width time and seq. num. */
> };
>
> struct pps_kparams {
> @@ -96,6 +110,11 @@ struct pps_kparams {
> #define PPS_CAPTURECLEAR 0x02 /* capture clear events */
> #define PPS_CAPTUREBOTH 0x03 /* capture assert and clear events */
>
> +/* Pulse-width calculation */
> +#define PPS_WIDTHASSERT 0x04 /* calculate assert width */
> +#define PPS_WIDTHCLEAR 0x08 /* calculate clear width */
> +#define PPS_WIDTHBOTH 0x0c /* calculate assert and clear width */
> +
I don't understand why a process should ask for just PPS_WIDTHASSERT or
PPS_WIDTHCLEAR... I think you can avoid defining these values and just enabling
pulse width calculation when both assert and clear events are available.
> #define PPS_OFFSETASSERT 0x10 /* apply compensation for assert event */
> #define PPS_OFFSETCLEAR 0x20 /* apply compensation for clear event */
However, the real point is: since an userpsace program can retrieve the time of
assert and clear events, why it cannot compute the pulses width by itself? :)
Ciao,
Rodolfo
--
GNU/Linux Solutions e-mail: giometti@...eenne.com
Linux Device Driver giometti@...ux.it
Embedded Systems phone: +39 349 2432127
UNIX programming skype: rodolfo.giometti
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