From 737ced8fa6ab0cfd0e139e0fd9d3a09cb404f4ab Mon Sep 17 00:00:00 2001
From: Andrew Dennison <andrew@motec.com.au>
Date: Mon, 13 Nov 2023 12:07:35 +1100
Subject: [PATCH] soc/software: add irq_attach() / irq_detach()

cleaner mechanism for other software to use interrupts
---
 litex/soc/integration/soc.py      |  1 +
 litex/soc/software/include/irq.h  | 15 +++++++++++
 litex/soc/software/libbase/isr.c  | 45 ++++++++++++++++++++++++-------
 litex/soc/software/libbase/uart.c |  2 ++
 4 files changed, 54 insertions(+), 9 deletions(-)
 create mode 100644 litex/soc/software/include/irq.h

diff --git a/litex/soc/integration/soc.py b/litex/soc/integration/soc.py
index fee8de48c..d12c27c23 100644
--- a/litex/soc/integration/soc.py
+++ b/litex/soc/integration/soc.py
@@ -1320,6 +1320,7 @@ class SoC(LiteXModule, SoCCoreCompat):
 
         # SoC IRQ Interconnect ---------------------------------------------------------------------
         if hasattr(self, "cpu") and hasattr(self.cpu, "interrupt"):
+            self.add_constant("NR_IRQ", max(self.irq.locs.values()) + 1)
             for name, loc in sorted(self.irq.locs.items()):
                 if name in self.cpu.interrupts.keys():
                     continue
diff --git a/litex/soc/software/include/irq.h b/litex/soc/software/include/irq.h
new file mode 100644
index 000000000..fa7a1411b
--- /dev/null
+++ b/litex/soc/software/include/irq.h
@@ -0,0 +1,15 @@
+#pragma once
+#include_next<irq.h>
+
+typedef void (*isr_t)(void);
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+extern int irq_attach(unsigned int irq, isr_t isr) __attribute__((weak));
+extern int irq_detach(unsigned int irq) __attribute__((weak));
+
+#ifdef __cplusplus
+}
+#endif
diff --git a/litex/soc/software/libbase/isr.c b/litex/soc/software/libbase/isr.c
index ac7a7920c..6c052b2d7 100644
--- a/litex/soc/software/libbase/isr.c
+++ b/litex/soc/software/libbase/isr.c
@@ -191,18 +191,45 @@ void isr(void)
 }
 
 #else
+struct irq_table
+{
+	isr_t isr;
+} irq_table[NR_IRQ];
+
+int irq_attach(unsigned int irq, isr_t isr)
+{
+	if (irq >= NR_IRQ) {
+		printf("Inv irq %d\n", irq);
+		return -1;
+	}
+
+	unsigned int ie = irq_getie();
+	irq_setie(0);
+	irq_table[irq].isr = isr;
+	irq_setie(ie);
+	return irq;
+}
+
+int irq_detach(unsigned int irq)
+{
+	return irq_attach(irq, NULL);
+}
+
 void isr(void)
 {
-	__attribute__((unused)) unsigned int irqs;
+	unsigned int irqs = irq_pending() & irq_getmask();
 
-	irqs = irq_pending() & irq_getmask();
-
-#ifdef CSR_UART_BASE
-#ifndef UART_POLLING
-	if(irqs & (1 << UART_INTERRUPT))
-		uart_isr();
-#endif
-#endif
+	while (irqs)
+	{
+		const unsigned int irq = __builtin_ctz(irqs);
+		if (irq < NR_IRQ && irq_table[irq].isr)
+			irq_table[irq].isr();
+		else {
+			irq_setmask(irq_getmask() & ~(1<<irq));
+			printf("\n*** disabled spurious irq %d ***\n", irq);
+		}
+		irqs &= irqs - 1; // clear this irq (the first bit set)
+	}
 }
 #endif
 
diff --git a/litex/soc/software/libbase/uart.c b/litex/soc/software/libbase/uart.c
index 87ee2654e..20a4dc271 100644
--- a/litex/soc/software/libbase/uart.c
+++ b/litex/soc/software/libbase/uart.c
@@ -110,6 +110,8 @@ void uart_init(void)
 
 	uart_ev_pending_write(uart_ev_pending_read());
 	uart_ev_enable_write(UART_EV_TX | UART_EV_RX);
+	if (irq_attach)
+		irq_attach(UART_INTERRUPT, uart_isr);
 	irq_setmask(irq_getmask() | (1 << UART_INTERRUPT));
 }