riscv: irq: Correct interrupt handling in clic non-vectored mode

According to the clic specification
(https://github.com/riscv/riscv-fast-interrupt), the mnxti register has
be written, in order to clear the pending bit for non-vectored
interrupts. For vectored interrupts, this is automatically done.

From the spec:
"If the pending interrupt is edge-triggered, hardware will automatically
clear the corresponding pending bit when the CSR instruction that
accesses xnxti includes a write."

I added a kconfig `RISCV_SOC_HAS_CUSTOM_IRQ_HANDLING` to allow custom
irq handling. If enabled, `__soc_handle_all_irqs` has to be implemented.

For clic, non-vectored mode, I added a `__soc_handle_all_irqs`, that
handles the pending interrupts according to the pseudo code in the spec.

Signed-off-by: Greter Raffael <rgreter@baumer.com>

arch/riscv/Kconfig

@@ -84,6 +84,13 @@ config RISCV_SOC_HAS_ISR_STACKING
 	    saved on the stack by the hardware, and the registers saved by the
 	    software macros. The structure must be called '__esf'.
 
+config RISCV_SOC_HAS_CUSTOM_IRQ_HANDLING
+	bool
+	help
+	  This allows the SoC to overwrite the irq handling. If enabled, the
+	  function __soc_handle_all_irqs has to be implemented. It shall service
+	  and clear all pending interrupts.
+
 config RISCV_SOC_HAS_CUSTOM_IRQ_LOCK_OPS
 	bool
 	help

arch/riscv/core/isr.S

@@ -73,6 +73,10 @@ GTEXT(sys_trace_isr_exit)
 GDATA(_k_syscall_table)
 #endif
 
+#ifdef CONFIG_RISCV_SOC_HAS_CUSTOM_IRQ_HANDLING
+GTEXT(__soc_handle_all_irqs)
+#endif
+
 /* exports */
 GTEXT(_isr_wrapper)
 
@@ -522,6 +526,10 @@ is_interrupt:
 
 on_irq_stack:
 
+#ifdef CONFIG_RISCV_SOC_HAS_CUSTOM_IRQ_HANDLING
+	call __soc_handle_all_irqs
+#else
+
 #ifdef CONFIG_TRACING_ISR
 	call sys_trace_isr_enter
 #endif
@@ -558,6 +566,8 @@ on_irq_stack:
 	call sys_trace_isr_exit
 #endif
 
+#endif
+
 irq_done:
 	/* Decrement _current_cpu->nested */
 	lw t2, ___cpu_t_nested_OFFSET(s0)

drivers/interrupt_controller/CMakeLists.txt

@@ -32,6 +32,7 @@ zephyr_library_sources_ifdef(CONFIG_SWERV_PIC               intc_swerv_pic.c)
 zephyr_library_sources_ifdef(CONFIG_VEXRISCV_LITEX_IRQ      intc_vexriscv_litex.c)
 zephyr_library_sources_ifdef(CONFIG_VIM                     intc_vim.c)
 zephyr_library_sources_ifdef(CONFIG_NUCLEI_ECLIC            intc_nuclei_eclic.c)
+zephyr_library_sources_ifdef(CONFIG_NUCLEI_ECLIC            intc_nuclei_eclic.S)
 zephyr_library_sources_ifdef(CONFIG_NXP_S32_EIRQ            intc_eirq_nxp_s32.c)
 zephyr_library_sources_ifdef(CONFIG_NXP_S32_WKPU            intc_wkpu_nxp_s32.c)
 zephyr_library_sources_ifdef(CONFIG_XMC4XXX_INTC            intc_xmc4xxx.c)

drivers/interrupt_controller/Kconfig.clic

@@ -6,6 +6,7 @@ config NUCLEI_ECLIC
 	default y
 	depends on DT_HAS_NUCLEI_ECLIC_ENABLED
 	select MULTI_LEVEL_INTERRUPTS
+	select RISCV_SOC_HAS_CUSTOM_IRQ_HANDLING if !RISCV_VECTORED_MODE
 	help
 	  Interrupt controller for Nuclei SoC core.
 

drivers/interrupt_controller/intc_nuclei_eclic.S

@@ -0,0 +1,79 @@
+/*
+ * Copyright (c) 2024 Baumer Electric AG
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/**
+ * @brief Assembler-hooks specific to Nuclei's Extended Core Interrupt Controller
+ */
+
+#include <zephyr/arch/cpu.h>
+
+
+GTEXT(__soc_handle_irq)
+/*
+ * In an ECLIC, pending interrupts don't have to be cleared by hand.
+ * In vectored mode, interrupts are cleared automatically.
+ * In non-vectored mode, interrupts are cleared when writing the mnxti register (done in
+ * __soc_handle_all_irqs).
+ * Thus this function can directly return.
+ */
+SECTION_FUNC(exception.other, __soc_handle_irq)
+	ret
+
+#if !defined(CONFIG_RISCV_VECTORED_MODE)
+
+GTEXT(__soc_handle_all_irqs)
+
+#ifdef CONFIG_TRACING
+/* imports */
+GTEXT(sys_trace_isr_enter)
+GTEXT(sys_trace_isr_exit)
+#endif
+
+/*
+ * This function services and clears all pending interrupts for an ECLIC in non-vectored mode.
+ */
+SECTION_FUNC(exception.other, __soc_handle_all_irqs)
+	mv t2, ra
+
+	/* Read and clear mnxti to get highest current interrupt and enable interrupts. Will return
+	 * original interrupt if no others appear. */
+	csrrci a0, 0x345, MSTATUS_IEN
+	beqz a0, irq_done /* Check if original interrupt vanished. */
+
+irq_loop:
+
+#ifdef CONFIG_TRACING_ISR
+	call sys_trace_isr_enter
+#endif
+
+	/* Call corresponding registered function in _sw_isr_table. a0 is offset in words, table is
+	 * 2-word wide -> shift by one */
+	la t0, _sw_isr_table
+	slli a0, a0, (1)
+	add t0, t0, a0
+
+	/* Load argument in a0 register */
+	lw a0, 0(t0)
+
+	/* Load ISR function address in register t1 */
+	lw t1, RV_REGSIZE(t0)
+
+	/* Call ISR function */
+	jalr ra, t1, 0
+
+	/* Read and clear mnxti to get highest current interrupt and enable interrupts. */
+	csrrci a0, 0x345, MSTATUS_IEN
+
+#ifdef CONFIG_TRACING_ISR
+	call sys_trace_isr_exit
+#endif
+
+	bnez a0, irq_loop
+
+irq_done:
+	mv ra, t2
+	ret
+#endif