soc/software: add irq_attach() / irq_detach()

cleaner mechanism for other software to use interrupts

NOTE: uart_isr(void) not changed to uart_isr(int) for compatibility
with cpus that don't implement this interface yet.

litex/soc/software/include/irq.h

@@ -0,0 +1,15 @@
+#pragma once
+#include_next<irq.h>
+
+typedef void (*isr_t)(int);
+
+#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

litex/soc/software/libbase/isr.c

@@ -191,18 +191,46 @@ void isr(void)
 }
 
 #else
-void isr(void)
+#define NR_IRQ 32
+struct irq_table
 {
-	__attribute__((unused)) unsigned int irqs;
+	void (*isr)(int);
+} irq_table[NR_IRQ];
 
-	irqs = irq_pending() & irq_getmask();
+int irq_attach(unsigned int irq, void (*isr)(int))
+{
+	if (irq >= NR_IRQ) {
+		printf("Inv irq %d\n", irq);
+		return -1;
+	}
 
-#ifdef CSR_UART_BASE
-#ifndef UART_POLLING
-	if(irqs & (1 << UART_INTERRUPT))
-		uart_isr();
-#endif
-#endif
+	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)
+{
+	unsigned int irqs = irq_pending() & irq_getmask();
+
+	while (irqs)
+	{
+		const unsigned int irq = __builtin_ctz(irqs);
+		if (irq_table[irq].isr)
+			irq_table[irq].isr(irq);
+		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
 

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, (isr_t)uart_isr);
 	irq_setmask(irq_getmask() | (1 << UART_INTERRUPT));
 }