From 995cf4dba0b01af66ed94fff0b485a75fdeb9c16 Mon Sep 17 00:00:00 2001
From: Alessandro Rubini <rubini@gnudd.com>
Date: Wed, 3 Dec 2014 15:47:19 +0100
Subject: [PATCH] kernel: add a clocksource module for WR time
Signed-off-by: Alessandro Rubini <rubini@gnudd.com>
---
kernel/Makefile | 2 +-
kernel/wr_clocksource/Makefile | 25 ++++
kernel/wr_clocksource/wr_clocksource.c | 173 +++++++++++++++++++++++++
3 files changed, 199 insertions(+), 1 deletion(-)
create mode 100644 kernel/wr_clocksource/Makefile
create mode 100644 kernel/wr_clocksource/wr_clocksource.c
diff --git a/kernel/Makefile b/kernel/Makefile
index 7534f5d89..b04218a4e 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -1,5 +1,5 @@
-DIRS = wr_vic wr_nic wr_rtu at91_softpwm wr_pstats
+DIRS = wr_vic wr_nic wr_rtu at91_softpwm wr_pstats wr_clocksource
# We may "LINUX ?= /usr/src/linux-wrswitch", but it's better to leave it empty
diff --git a/kernel/wr_clocksource/Makefile b/kernel/wr_clocksource/Makefile
new file mode 100644
index 000000000..f96375737
--- /dev/null
+++ b/kernel/wr_clocksource/Makefile
@@ -0,0 +1,25 @@
+obj-m := wr_clocksource.o
+
+# accept WRN_DEBUG from the environment. It turns pr_debug() into printk.
+ifdef WRN_DEBUG
+ ccflags-y += -DDEBUG
+endif
+
+# What follows is standard stuff
+export ARCH ?= arm
+export CROSS_COMPILE ?= $(CROSS_COMPILE_ARM)
+
+all modules:
+ $(MAKE) CONFIG_DEBUG_SECTION_MISMATCH=y \
+ -C $(LINUX) SUBDIRS=$(shell /bin/pwd) modules
+
+# looking at preprocessed output is helpful for bug hunting
+preprocess:
+ $(MAKE) CONFIG_DEBUG_SECTION_MISMATCH=y \
+ -C $(LINUX) SUBDIRS=$(shell /bin/pwd) $(wr-nic-objs:.o=.i)
+
+# We might "$(MAKE) -C $(LINUX)" but "make clean" with no LINUX defined
+# is sometimes useful to have
+clean:
+ rm -f *.mod.c *.o *.ko *.i .*cmd Module.symvers modules.order *~
+ rm -rf .tmp_versions
diff --git a/kernel/wr_clocksource/wr_clocksource.c b/kernel/wr_clocksource/wr_clocksource.c
new file mode 100644
index 000000000..9a2a1508c
--- /dev/null
+++ b/kernel/wr_clocksource/wr_clocksource.c
@@ -0,0 +1,173 @@
+/* Alessandro Rubini for CERN 2014, GPLv2 or later */
+#include <linux/module.h>
+#include <linux/moduleparam.h>
+#include <linux/init.h>
+#include <linux/timer.h>
+#include <linux/jiffies.h>
+#include <linux/vmalloc.h>
+#include <linux/clocksource.h>
+
+/* We need these two defined in order to include nic-hardware.h */
+#define WR_IS_NODE 0
+#define WR_IS_SWITCH 1
+
+/* We have no centralized defines yet: pick frequency and registers base */
+#include "../wr_nic/nic-hardware.h"
+#define WRCS_FREQUENCY REFCLK_FREQ
+#define WRCS_TICK_NS (NSEC_PER_SEC / WRCS_FREQUENCY)
+
+static int wrcs_stats;
+module_param(wrcs_stats, int, 0644);
+MODULE_PARM_DESC(wrcs_stats, "Count how often the clocksource is being read");
+
+static __iomem struct PPSG_WB *wrcs_ppsg;
+
+static int wrcs_is_registered; /* no need for atomic_t or whatever */
+
+/* If so requested, print statistics once per second */
+static inline void wrcs_do_stats(void)
+{
+ static unsigned long nextp;
+ static int ncalls;
+
+ if (!wrcs_stats)
+ return;
+
+ if (!nextp)
+ nextp = jiffies + HZ;
+
+ /* This, when enabled, shows around 400 calls per second */
+ if (time_after_eq(jiffies, nextp)) {
+ pr_info("%s: called %i times\n", __func__,
+ ncalls);
+ ncalls = 0;
+ nextp += HZ;
+ }
+ ncalls++;
+}
+
+static cycle_t wrcs_read(struct clocksource *cs)
+{
+ static uint32_t offset, last, this;
+
+ wrcs_do_stats();
+
+ /* FIXME: identify a time jump by monitoring the tick counter */
+
+ /*
+ * Turn the counter into a 32-bit one (see cs->mask below).
+ * We reset at 0x3b9aca0, so without this we should use mask = 0x1f
+ * and mac_idle = 32 ticks = 512ns. Unaffordable.
+ */
+ this = readl(&wrcs_ppsg->CNTR_NSEC);
+ if (this < last)
+ offset += WRCS_FREQUENCY;
+ last = this;
+ return offset + this;
+}
+
+
+static struct clocksource wrcs_cs = {
+ .name = "white-rabbit",
+ .rating = 450, /* perfect... */
+ .read = wrcs_read,
+ /* no enable/disable */
+ .mask = 0xffffffff, /* We fake a 32-bit thing */
+ .max_idle_ns = 900 * 1000 * 1000, /* well, 1s... */
+ .flags = CLOCK_SOURCE_IS_CONTINUOUS,
+};
+
+/*
+ * The timer is used to check when does WR synchronize. When that
+ * happens, we set time of day and register our clocksource. Time
+ * jumps after synchronization are not well supported.
+ */
+static void wrcs_timer_fn(unsigned long unused);
+static DEFINE_TIMER(wrcs_timer, wrcs_timer_fn, 0, 0);
+
+static void wrcs_timer_fn(unsigned long unused)
+{
+ uint32_t ticks, tai_l, tai_h;
+ int64_t tai;
+
+ /* Read ppsg, all fields consistently se we can use the value */
+ do {
+ tai_l = readl(&wrcs_ppsg->CNTR_UTCLO);
+ tai_h = readl(&wrcs_ppsg->CNTR_UTCHI);
+ ticks = readl(&wrcs_ppsg->CNTR_NSEC);
+ } while (readl(&wrcs_ppsg->CNTR_UTCLO) != tai_l);
+ tai = (typeof(tai))tai_h << 32 | tai_l;
+
+ /* If we are before 2010 (date +%s --date=2010-01-01), try again */
+ if (tai < 1262300400LL) {
+ mod_timer(&wrcs_timer, jiffies + HZ);
+ return;
+ }
+
+ clocksource_register(&wrcs_cs);
+ wrcs_is_registered = 1;
+ /* And don't restart the timer */
+}
+
+static int wrcs_init(void)
+{
+ wrcs_ppsg = ioremap(FPGA_BASE_PPSG, FPGA_SIZE_PPSG);
+ if (!wrcs_ppsg) {
+ pr_err("WR Clocksource: can't remap PPS registers\n");
+ return -EIO;
+ }
+
+ clocksource_calc_mult_shift(&wrcs_cs, WRCS_FREQUENCY, 1);
+
+ /* Fire the timer */
+ mod_timer(&wrcs_timer, jiffies + HZ);
+ return 0;
+}
+
+static void wrcs_exit(void)
+{
+ del_timer_sync(&wrcs_timer);
+ if (wrcs_is_registered)
+ clocksource_unregister(&wrcs_cs);
+ iounmap(wrcs_ppsg);
+}
+
+
+module_init(wrcs_init);
+module_exit(wrcs_exit);
+
+MODULE_LICENSE("GPL");
+
+
+/* Hack: this is not exported by current kernel. Define a local copy */
+void
+clocks_calc_mult_shift(u32 *mult, u32 *shift, u32 from, u32 to, u32 maxsec)
+{
+ u64 tmp;
+ u32 sft, sftacc= 32;
+
+ /*
+ * Calculate the shift factor which is limiting the conversion
+ * range:
+ */
+ tmp = ((u64)maxsec * from) >> 32;
+ while (tmp) {
+ tmp >>=1;
+ sftacc--;
+ }
+
+ /*
+ * Find the conversion shift/mult pair which has the best
+ * accuracy and fits the maxsec conversion range:
+ */
+ for (sft = 32; sft > 0; sft--) {
+ tmp = (u64) to << sft;
+ tmp += from / 2;
+ do_div(tmp, from);
+ if ((tmp >> sftacc) == 0)
+ break;
+ }
+ *mult = tmp;
+ *shift = sft;
+}
+
--
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