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iichid(4): Improve idle sampling hysteresis

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In sampling mode some devices return same data indefinitely even if
there is nothing to report.  Previous idle hysteresis implementation
activated only when device returned no data, so some devices ended up
polled at fast rate all the time.  This new implementation compares
each new report with the previous, and, if they are identical, after
reaching threshold also drop sampling rate to slow.

On my Dell XPS 13 9310 with iichid(4) touchscreen and touchpad this
reduces idle power consumption by ~0.5W by reducing number of context
switches in the driver from ~4000 to ~700 per second when not touched.

MFC after:	1 month
This commit is contained in:
Alexander Motin 2023-12-22 22:50:52 -05:00
parent eebb9c2cae
commit 8c86b98124
1 changed files with 29 additions and 10 deletions
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39
sys/dev/iicbus/iichid.c
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@ -108,7 +108,7 @@ enum {
*/
#define IICHID_SAMPLING_RATE_FAST 60
#define IICHID_SAMPLING_RATE_SLOW 10
#define IICHID_SAMPLING_HYSTERESIS 1
#define IICHID_SAMPLING_HYSTERESIS 12 /* ~ 2x fast / slow */
/* 5.1.1 - HID Descriptor Format */
struct i2c_hid_desc {
@ -177,9 +177,12 @@ struct iichid_softc {
int sampling_rate_fast;
int sampling_hysteresis;
int missing_samples; /* iicbus lock */
struct timeout_task periodic_task; /* iicbus lock */
int dup_samples; /* iicbus lock */
iichid_size_t dup_size; /* iicbus lock */
bool callout_setup; /* iicbus lock */
uint8_t *dup_buf;
struct taskqueue *taskqueue;
struct timeout_task periodic_task; /* iicbus lock */
struct task event_task;
#endif
@ -523,7 +526,7 @@ iichid_event_task(void *context, int pending)
device_t parent;
iichid_size_t actual;
bool bus_requested;
int error;
int error, rate;
sc = context;
parent = device_get_parent(sc->dev);
@ -541,18 +544,30 @@ iichid_event_task(void *context, int pending)
if (actual > 0) {
sc->intr_handler(sc->intr_ctx, sc->intr_buf, actual);
sc->missing_samples = 0;
} else
++sc->missing_samples;
if (sc->dup_size != actual ||
memcmp(sc->dup_buf, sc->intr_buf, actual) != 0) {
sc->dup_size = actual;
memcpy(sc->dup_buf, sc->intr_buf, actual);
sc->dup_samples = 0;
} else
++sc->dup_samples;
} else {
if (++sc->missing_samples == 1)
sc->intr_handler(sc->intr_ctx, sc->intr_buf, 0);
sc->dup_samples = 0;
}
} else
DPRINTF(sc, "read error occurred: %d\n", error);
rearm:
if (sc->callout_setup && sc->sampling_rate_slow > 0) {
if (sc->missing_samples == sc->sampling_hysteresis)
sc->intr_handler(sc->intr_ctx, sc->intr_buf, 0);
taskqueue_enqueue_timeout(sc->taskqueue, &sc->periodic_task,
hz / MAX(sc->missing_samples >= sc->sampling_hysteresis ?
sc->sampling_rate_slow : sc->sampling_rate_fast, 1));
if (sc->missing_samples >= sc->sampling_hysteresis ||
sc->dup_samples >= sc->sampling_hysteresis)
rate = sc->sampling_rate_slow;
else
rate = sc->sampling_rate_fast;
taskqueue_enqueue_timeout_sbt(sc->taskqueue, &sc->periodic_task,
SBT_1S / MAX(rate, 1), 0, C_PREL(1));
}
out:
if (bus_requested)
@ -725,6 +740,8 @@ iichid_reset_callout(struct iichid_softc *sc)
/* Start with slow sampling. */
sc->missing_samples = sc->sampling_hysteresis;
sc->dup_samples = 0;
sc->dup_size = 0;
taskqueue_enqueue(sc->taskqueue, &sc->event_task);
return (0);
@ -812,6 +829,7 @@ iichid_intr_setup(device_t dev, device_t child __unused, hid_intr_t intr,
sc->intr_buf = malloc(rdesc->rdsize, M_DEVBUF, M_WAITOK | M_ZERO);
sc->intr_bufsize = rdesc->rdsize;
#ifdef IICHID_SAMPLING
sc->dup_buf = malloc(rdesc->rdsize, M_DEVBUF, M_WAITOK | M_ZERO);
taskqueue_start_threads(&sc->taskqueue, 1, PI_TTY,
"%s taskq", device_get_nameunit(sc->dev));
#endif
@ -825,6 +843,7 @@ iichid_intr_unsetup(device_t dev, device_t child __unused)
sc = device_get_softc(dev);
#ifdef IICHID_SAMPLING
taskqueue_drain_all(sc->taskqueue);
free(sc->dup_buf, M_DEVBUF);
#endif
free(sc->intr_buf, M_DEVBUF);
}