Author: ian
Date: Tue Sep 10 22:08:34 2019
New Revision: 352196
URL: https://svnweb.freebsd.org/changeset/base/352196
Log:
In am335x_dmtpps, use a spin mutex to interlock between PPS capture and PPS
ioctl(2) handling. This allows doing the pps_event() work in the polling
routine, instead of using a taskqueue task to do that work.
Also, add PNPINFO, and switch to using make_dev_s() to create the cdev.
Using a spin mutex and calling pps_event() from the polling function works
around the situation which requires more than 2 sets of timecounter
timehands in a single-core system to get reliable PPS capture. That problem
would happen when a single-core system is idle in cpu_idle() then gets woken
up with an event timer event which was scheduled to handle a hardclock tick.
That processing path would end up calling tc_windup 3 or 4 times between
when the tc polling function was called and when the taskqueue task would
eventually run, and with only two sets of timehands, the th_generation count
would always be too old to allow the captured PPS data to be used.
Modified:
head/sys/arm/ti/am335x/am335x_dmtpps.c
Modified: head/sys/arm/ti/am335x/am335x_dmtpps.c
==============================================================================
--- head/sys/arm/ti/am335x/am335x_dmtpps.c Tue Sep 10 21:53:42 2019
(r352195)
+++ head/sys/arm/ti/am335x/am335x_dmtpps.c Tue Sep 10 22:08:34 2019
(r352196)
@@ -52,7 +52,6 @@ __FBSDID("$FreeBSD$");
#include <sys/malloc.h>
#include <sys/mutex.h>
#include <sys/rman.h>
-#include <sys/taskqueue.h>
#include <sys/timepps.h>
#include <sys/timetc.h>
#include <machine/bus.h>
@@ -79,7 +78,6 @@ struct dmtpps_softc {
uint32_t tclr; /* Cached TCLR register. */
struct timecounter tc;
int pps_curmode; /* Edge mode now set in hw. */
- struct task pps_task; /* For pps_event handling. */
struct cdev * pps_cdev;
struct pps_state pps_state;
struct mtx pps_mtx;
@@ -93,6 +91,7 @@ static struct ofw_compat_data compat_data[] = {
{"ti,am335x-timer-1ms", 1},
{NULL, 0},
};
+SIMPLEBUS_PNP_INFO(compat_data);
/*
* A table relating pad names to the hardware timer number they can be mux'd
to.
@@ -285,48 +284,29 @@ dmtpps_poll(struct timecounter *tc)
* populates it from the current DMT_TCRR register) with the latched
* value from the TCAR1 register.
*
- * There is no locking here, by design. pps_capture() writes into an
- * area of struct pps_state which is read only by pps_event(). The
- * synchronization of access to that area is temporal rather than
- * interlock based... we write in this routine and trigger the task that
- * will read the data, so no simultaneous access can occur.
- *
* Note that we don't have the TCAR interrupt enabled, but the hardware
* still provides the status bits in the "RAW" status register even when
* they're masked from generating an irq. However, when clearing the
* TCAR status to re-arm the capture for the next second, we have to
* write to the IRQ status register, not the RAW register. Quirky.
+ *
+ * We do not need to hold a lock while capturing the pps data, because
+ * it is captured into an area of the pps_state struct which is read
+ * only by pps_event(). We do need to hold a lock while calling
+ * pps_event(), because it manipulates data which is also accessed from
+ * the ioctl(2) context by userland processes.
*/
if (DMTIMER_READ4(sc, DMT_IRQSTATUS_RAW) & DMT_IRQ_TCAR) {
pps_capture(&sc->pps_state);
sc->pps_state.capcount = DMTIMER_READ4(sc, DMT_TCAR1);
DMTIMER_WRITE4(sc, DMT_IRQSTATUS, DMT_IRQ_TCAR);
- taskqueue_enqueue(taskqueue_fast, &sc->pps_task);
+
+ mtx_lock_spin(&sc->pps_mtx);
+ pps_event(&sc->pps_state, PPS_CAPTUREASSERT);
+ mtx_unlock_spin(&sc->pps_mtx);
}
}
-static void
-dmtpps_event(void *arg, int pending)
-{
- struct dmtpps_softc *sc;
-
- sc = arg;
-
- /* This is the task function that gets enqueued by poll_pps. Once the
- * time has been captured by the timecounter polling code which runs in
- * primary interrupt context, the remaining (more expensive) work to
- * process the event is done later in a threaded context.
- *
- * Here there is an interlock that protects the event data in struct
- * pps_state. That data can be accessed at any time from userland via
- * ioctl() calls so we must ensure that there is no read access to
- * partially updated data while pps_event() does its work.
- */
- mtx_lock(&sc->pps_mtx);
- pps_event(&sc->pps_state, PPS_CAPTUREASSERT);
- mtx_unlock(&sc->pps_mtx);
-}
-
static int
dmtpps_open(struct cdev *dev, int flags, int fmt,
struct thread *td)
@@ -374,9 +354,9 @@ dmtpps_ioctl(struct cdev *dev, u_long cmd, caddr_t dat
sc = dev->si_drv1;
/* Let the kernel do the heavy lifting for ioctl. */
- mtx_lock(&sc->pps_mtx);
+ mtx_lock_spin(&sc->pps_mtx);
err = pps_ioctl(cmd, data, &sc->pps_state);
- mtx_unlock(&sc->pps_mtx);
+ mtx_unlock_spin(&sc->pps_mtx);
if (err != 0)
return (err);
@@ -436,6 +416,7 @@ static int
dmtpps_attach(device_t dev)
{
struct dmtpps_softc *sc;
+ struct make_dev_args mda;
clk_ident_t timer_id;
int err, sysclk_freq;
@@ -502,22 +483,27 @@ dmtpps_attach(device_t dev)
* now, just say we can only capture assert events (the positive-going
* edge of the pulse).
*/
- mtx_init(&sc->pps_mtx, "dmtpps", NULL, MTX_DEF);
+ mtx_init(&sc->pps_mtx, "dmtpps", NULL, MTX_SPIN);
+ sc->pps_state.flags = PPSFLAG_MTX_SPIN;
sc->pps_state.ppscap = PPS_CAPTUREASSERT;
sc->pps_state.driver_abi = PPS_ABI_VERSION;
sc->pps_state.driver_mtx = &sc->pps_mtx;
pps_init_abi(&sc->pps_state);
- /*
- * Init the task that does deferred pps_event() processing after
- * the polling routine has captured a pps pulse time.
- */
- TASK_INIT(&sc->pps_task, 0, dmtpps_event, sc);
-
/* Create the PPS cdev. */
- sc->pps_cdev = make_dev(&dmtpps_cdevsw, 0, UID_ROOT, GID_WHEEL, 0600,
- PPS_CDEV_NAME);
- sc->pps_cdev->si_drv1 = sc;
+ make_dev_args_init(&mda);
+ mda.mda_flags = MAKEDEV_WAITOK;
+ mda.mda_devsw = &dmtpps_cdevsw;
+ mda.mda_cr = NULL;
+ mda.mda_uid = UID_ROOT;
+ mda.mda_gid = GID_WHEEL;
+ mda.mda_mode = 0600;
+ mda.mda_unit = device_get_unit(dev);
+ mda.mda_si_drv1 = sc;
+ if ((err = make_dev_s(&mda, &sc->pps_cdev, PPS_CDEV_NAME)) != 0) {
+ device_printf(dev, "Failed to create cdev %s\n", PPS_CDEV_NAME);
+ return (err);
+ }
if (bootverbose)
device_printf(sc->dev, "Using %s for PPS device /dev/%s\n",
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