[LinuxPPS] [PATCH 09/11] pps: low level IRQ timestamps recording.

[Rodolfo Giometti]

Add low level IRQ timestamps recording for x86 (32 and 64 bits)
platforms and enable UART clients in order to use it.

This improves PPS precision. :)

Signed-off-by: Rodolfo Giometti <giometti at linux.it>
---
 arch/x86/kernel/irq_32.c    |    2 +
 arch/x86/kernel/irq_64.c    |    2 +
 drivers/pps/Kconfig         |   12 +++++++++++
 include/linux/irqnr.h       |    4 +++
 include/linux/serial_core.h |    5 ++++
 kernel/irq/handle.c         |   46 +++++++++++++++++++++++++++++++++++++++++++
 6 files changed, 71 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kernel/irq_32.c b/arch/x86/kernel/irq_32.c
index 3b09634..f8cb7e5 100644
--- a/arch/x86/kernel/irq_32.c
+++ b/arch/x86/kernel/irq_32.c
@@ -199,6 +199,8 @@ bool handle_irq(unsigned irq, struct pt_regs *regs)
 
 	overflow = check_stack_overflow();
 
+	irq_save_ts(irq);
+
 	desc = irq_to_desc(irq);
 	if (unlikely(!desc))
 		return false;
diff --git a/arch/x86/kernel/irq_64.c b/arch/x86/kernel/irq_64.c
index 977d8b4..afbdba0 100644
--- a/arch/x86/kernel/irq_64.c
+++ b/arch/x86/kernel/irq_64.c
@@ -54,6 +54,8 @@ bool handle_irq(unsigned irq, struct pt_regs *regs)
 
 	stack_overflow_check(regs);
 
+	irq_save_ts(irq);
+
 	desc = irq_to_desc(irq);
 	if (unlikely(!desc))
 		return false;
diff --git a/drivers/pps/Kconfig b/drivers/pps/Kconfig
index 1afe4e0..6e8a2aa 100644
--- a/drivers/pps/Kconfig
+++ b/drivers/pps/Kconfig
@@ -22,6 +22,18 @@ config PPS
 	  To compile this driver as a module, choose M here: the module
 	  will be called pps_core.ko.
 
+config PPS_IRQ_EVENTS
+	bool "Use low level IRQ timestamps"
+	depends on PPS && (X86_32 || X86_64)
+	default no
+	help
+	  Say Y here if you wish using low level IRQ timestamps to register
+	  PPS events.
+
+	  This should improve PPS resolution but it delays echo functions
+	  call. Note also that this function may not be supported by some
+	  PPS clients!
+
 config PPS_DEBUG
 	bool "PPS debugging messages"
 	depends on PPS
diff --git a/include/linux/irqnr.h b/include/linux/irqnr.h
index ec87b21..44f4608 100644
--- a/include/linux/irqnr.h
+++ b/include/linux/irqnr.h
@@ -25,6 +25,7 @@
 
 extern int nr_irqs;
 extern struct irq_desc *irq_to_desc(unsigned int irq);
+extern struct timespec *irq_to_ts(unsigned int irq);
 
 # define for_each_irq_desc(irq, desc)					\
 	for (irq = 0, desc = irq_to_desc(irq); irq < nr_irqs;		\
@@ -43,6 +44,9 @@ extern struct irq_desc *irq_to_desc(unsigned int irq);
 
 #endif /* CONFIG_GENERIC_HARDIRQS */
 
+extern struct timespec *irq_to_ts(unsigned int irq);
+extern void irq_save_ts(unsigned int irq);
+
 #define for_each_irq_nr(irq)                   \
        for (irq = 0; irq < nr_irqs; irq++)
 
diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
index 9b5a4d1..659f685 100644
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@@ -184,6 +184,7 @@
 #include <linux/tty.h>
 #include <linux/mutex.h>
 #include <linux/sysrq.h>
+#include <linux/irqnr.h>
 
 struct uart_port;
 struct uart_info;
@@ -522,7 +523,11 @@ uart_handle_dcd_change(struct uart_port *port, unsigned int status)
 	struct timespec ts;
 
 	if (ld && ld->ops->dcd_change)
+#ifdef CONFIG_PPS_IRQ_EVENTS
+		ts = *(irq_to_ts(port->irq));
+#else
 		getnstimeofday(&ts);
+#endif
 
 	port->icount.dcd++;
 #ifdef CONFIG_HARD_PPS
diff --git a/kernel/irq/handle.c b/kernel/irq/handle.c
index 065205b..867200a 100644
--- a/kernel/irq/handle.c
+++ b/kernel/irq/handle.c
@@ -132,6 +132,7 @@ static void init_one_irq_desc(int irq, struct irq_desc *desc, int node)
 DEFINE_SPINLOCK(sparse_irq_lock);
 
 struct irq_desc **irq_desc_ptrs __read_mostly;
+struct timespec *irq_ts __read_mostly;
 
 static struct irq_desc irq_desc_legacy[NR_IRQS_LEGACY] __cacheline_aligned_in_smp = {
 	[0 ... NR_IRQS_LEGACY-1] = {
@@ -166,6 +167,9 @@ int __init early_irq_init(void)
 	/* allocate irq_desc_ptrs array based on nr_irqs */
 	irq_desc_ptrs = kcalloc(nr_irqs, sizeof(void *), GFP_NOWAIT);
 
+	/* allocate irq_ts array based on nr_irqs */
+	irq_ts = kcalloc(nr_irqs, sizeof(struct timespec), GFP_NOWAIT);
+
 	/* allocate based on nr_cpu_ids */
 	kstat_irqs_legacy = kzalloc_node(NR_IRQS_LEGACY * nr_cpu_ids *
 					  sizeof(int), GFP_NOWAIT, node);
@@ -193,6 +197,26 @@ struct irq_desc *irq_to_desc(unsigned int irq)
 	return NULL;
 }
 
+void irq_save_ts(unsigned int irq)
+{
+#ifdef CONFIG_PPS_IRQ_EVENTS
+	if (irq_desc_ptrs && irq < nr_irqs)
+		getnstimeofday(&irq_ts[irq]);
+#endif
+}
+
+struct timespec *irq_to_ts(unsigned int irq)
+{
+	if (irq >= nr_irqs) {
+		WARN(1, "irq (%d) >= nr_irqs (%d) in irq_to_ts\n",
+			irq, nr_irqs);
+		return NULL;
+	}
+
+	return &irq_ts[irq];
+}
+EXPORT_SYMBOL(irq_to_ts);
+
 struct irq_desc * __ref irq_to_desc_alloc_node(unsigned int irq, int node)
 {
 	struct irq_desc *desc;
@@ -247,6 +271,8 @@ struct irq_desc irq_desc[NR_IRQS] __cacheline_aligned_in_smp = {
 	}
 };
 
+struct timespec irq_ts[NR_IRQS] __cacheline_aligned_in_smp;
+
 static unsigned int kstat_irqs_all[NR_IRQS][NR_CPUS];
 int __init early_irq_init(void)
 {
@@ -275,6 +301,26 @@ struct irq_desc *irq_to_desc(unsigned int irq)
 	return (irq < NR_IRQS) ? irq_desc + irq : NULL;
 }
 
+void irq_save_ts(unsigned int irq)
+{
+#ifdef CONFIG_PPS_IRQ_EVENTS
+	if (irq < NR_IRQS)
+		getnstimeofday(&irq_ts[irq]);
+#endif
+}
+
+struct timespec *irq_to_ts(unsigned int irq)
+{
+	if (irq >= NR_IRQS) {
+		WARN(1, "irq (%d) >= nr_irqs (%d) in irq_to_ts\n",
+			irq, nr_irqs);
+		return NULL;
+	}
+
+	return &irq_ts[irq];
+}
+EXPORT_SYMBOL(irq_to_ts);
+
 struct irq_desc *irq_to_desc_alloc_node(unsigned int irq, int node)
 {
 	return irq_to_desc(irq);
-- 
1.6.0.4