Date: Tue, 10 Sep 2019 22:08:34 +0000 (UTC) From: Ian Lepore <ian@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r352196 - head/sys/arm/ti/am335x Message-ID: <201909102208.x8AM8YUP018427@repo.freebsd.org>
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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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