[PATCH v4 2/3] lib: sbi: Enable Smrnmi extension handler

[Nylon Chen]

Introduce rnmi_vector_init() which prepares the hart for Smrnmi:

  1. Checks if the hart supports Smrnmi extension
  2. Writes scratch pointer into MNSCRATCH (same role as MSCRATCH for
     the RNMI entry path)

The function is file-static and called at the end of sbi_hart_init()
so every hart (cold and warm) initializes its own RNMI state before
returning to the firmware boot sequence.

Add set_rnmi_trap_vector() to struct sbi_platform_operations:

  int (*set_rnmi_trap_vector)(unsigned long handler_addr, bool cold_boot);

Use 'unsigned long' rather than 'uintptr_t' for consistency with the
rest of the platform operations interface. Platforms that support Smrnmi
must implement this; others can leave it NULL.

Add suspend/resume support for RNMI CSRs (MNSCRATCH and MNSTATUS) to
ensure proper state preservation across non-retentive suspend.

Note: This patch does not yet enable RNMI interrupts. The trap vector
setup and MNSTATUS.NMIE enablement will be added in the next patch after
the trap handler is implemented.

Co-developed-by: Zong Li <zong.li at sifive.com>
Signed-off-by: Zong Li <zong.li at sifive.com>
Suggested-by: Nick Hu <nick.hu at sifive.com>
Suggested-by: Samuel Holland <samuel.holland at sifive.com>
Signed-off-by: Nylon Chen <nylon.chen at sifive.com>
Signed-off-by: Yong-Xuan Wang <yongxuan.wang at sifive.com>
---
 include/sbi/sbi_platform.h |  8 ++++++++
 lib/sbi/sbi_hart.c         | 27 ++++++++++++++++++++++++++-
 lib/sbi/sbi_hsm.c          | 14 ++++++++++++++
 3 files changed, 48 insertions(+), 1 deletion(-)

diff --git a/include/sbi/sbi_platform.h b/include/sbi/sbi_platform.h
index e65d9877..555e8b79 100644
--- a/include/sbi/sbi_platform.h
+++ b/include/sbi/sbi_platform.h
@@ -149,6 +149,14 @@ struct sbi_platform_operations {
 			unsigned long log2len);
 	/** platform specific pmp disable on current HART */
 	void (*pmp_disable)(unsigned int n);
+	/**
+	 * Platform-specific helper to program the RNMI trap vector.
+	 *
+	 * Called from rnmi_vector_init() with the firmware RNMI handler
+	 * entry address and the cold_boot flag. Platforms that support
+	 * Smrnmi must implement this; others can leave it NULL.
+	 */
+	int (*set_rnmi_trap_vector)(unsigned long handler_addr, bool cold_boot);
 };
 
 /** Platform default per-HART stack size for exception/interrupt handling */
diff --git a/lib/sbi/sbi_hart.c b/lib/sbi/sbi_hart.c
index 495ad1d8..eca6662f 100644
--- a/lib/sbi/sbi_hart.c
+++ b/lib/sbi/sbi_hart.c
@@ -29,6 +29,9 @@ void (*sbi_hart_expected_trap)(void) = &__sbi_expected_trap;
 
 unsigned long hart_features_offset;
 
+/* Forward declaration */
+static int rnmi_vector_init(struct sbi_scratch *scratch, bool cold_boot);
+
 static void mstatus_init(struct sbi_scratch *scratch)
 {
 	int cidx;
@@ -756,7 +759,29 @@ int sbi_hart_init(struct sbi_scratch *scratch, bool cold_boot)
 	if (rc)
 		return rc;
 
-	return sbi_hart_reinit(scratch);
+	rc = sbi_hart_reinit(scratch);
+	if (rc)
+		return rc;
+
+	return rnmi_vector_init(scratch, cold_boot);
+}
+
+static int rnmi_vector_init(struct sbi_scratch *scratch, bool cold_boot)
+{
+	/* If the hart does not support Smrnmi then nothing to do. */
+	if (!sbi_hart_has_extension(scratch, SBI_HART_EXT_SMRNMI))
+		return 0;
+
+	/*
+	 * Set MNSCRATCH to the scratch pointer (same role as MSCRATCH).
+	 * The RNMI handler (to be added in the next patch) will check
+	 * MNSTATUS.MNPP to determine whether to use the scratch area
+	 * (S/U-mode interrupted) or reuse the existing M-mode stack
+	 * (M-mode interrupted).
+	 */
+	csr_write(CSR_MNSCRATCH, (unsigned long)scratch);
+
+	return 0;
 }
 
 void __attribute__((noreturn)) sbi_hart_hang(void)
diff --git a/lib/sbi/sbi_hsm.c b/lib/sbi/sbi_hsm.c
index 0a355f9c..41115080 100644
--- a/lib/sbi/sbi_hsm.c
+++ b/lib/sbi/sbi_hsm.c
@@ -49,6 +49,8 @@ struct sbi_hsm_data {
 	unsigned long saved_medeleg;
 	unsigned long saved_mideleg;
 	u64 saved_menvcfg;
+	unsigned long saved_mnscratch;
+	unsigned long saved_mnstatus;
 	atomic_t start_ticket;
 };
 
@@ -430,6 +432,12 @@ void __sbi_hsm_suspend_non_ret_save(struct sbi_scratch *scratch)
 	hdata->saved_mideleg = csr_read(CSR_MIDELEG);
 	if (sbi_hart_priv_version(scratch) >= SBI_HART_PRIV_VER_1_12)
 		hdata->saved_menvcfg = csr_read64(CSR_MENVCFG);
+
+	/* Save RNMI CSRs if Smrnmi is supported */
+	if (sbi_hart_has_extension(scratch, SBI_HART_EXT_SMRNMI)) {
+		hdata->saved_mnscratch = csr_read(CSR_MNSCRATCH);
+		hdata->saved_mnstatus = csr_read(CSR_MNSTATUS);
+	}
 }
 
 static void __sbi_hsm_suspend_non_ret_restore(struct sbi_scratch *scratch)
@@ -443,6 +451,12 @@ static void __sbi_hsm_suspend_non_ret_restore(struct sbi_scratch *scratch)
 	csr_write(CSR_MEDELEG, hdata->saved_medeleg);
 	csr_write(CSR_MIE, hdata->saved_mie);
 	csr_set(CSR_MIP, (hdata->saved_mip & (MIP_SSIP | MIP_STIP)));
+
+	/* Restore RNMI CSRs if Smrnmi is supported */
+	if (sbi_hart_has_extension(scratch, SBI_HART_EXT_SMRNMI)) {
+		csr_write(CSR_MNSCRATCH, hdata->saved_mnscratch);
+		csr_write(CSR_MNSTATUS, hdata->saved_mnstatus);
+	}
 }
 
 void sbi_hsm_hart_resume_start(struct sbi_scratch *scratch)
-- 
2.43.7