[RFC PATCH 1/5] lib: sbi: Preserve stimecmp across domain switches

[whensun]

From: Theodorus Wensan Februanto <theodoruswensanfebruanto025 at gmail.com>

The Sstc extension provides a supervisor timer comparison register.
Without preserving this value, another domain can replace the
previous domain's timer deadline.

Keep a per-domain timer comparison value and initialize new domains
to a future deadline to avoid immediate timer interrupts.

Link: https://github.com/riscv-software-src/opensbi/issues/433
Signed-off-by: Theodorus Wensan Februanto <theodoruswensanfebruanto025 at gmail.com>
---
 lib/sbi/sbi_domain_context.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/lib/sbi/sbi_domain_context.c b/lib/sbi/sbi_domain_context.c
index 0861d541..26980658 100644
--- a/lib/sbi/sbi_domain_context.c
+++ b/lib/sbi/sbi_domain_context.c
@@ -50,6 +50,8 @@ struct hart_context {
 	unsigned long senvcfg;
 	/** Supervisor resource management configuration register */
 	unsigned long srmcfg;
+	/** Supervisor timer comparison register */
+	u64 stimecmp;
 
 	/** Float context state */
 	struct sbi_fp_context fp_ctx;
@@ -145,6 +147,8 @@ static int switch_to_next_domain_context(struct hart_context *ctx,
 		ctx->senvcfg	= csr_swap(CSR_SENVCFG, dom_ctx->senvcfg);
 	if (sbi_hart_has_extension(scratch, SBI_HART_EXT_SSQOSID))
 		ctx->srmcfg	= csr_swap(CSR_SRMCFG, dom_ctx->srmcfg);
+	if (sbi_hart_has_extension(scratch, SBI_HART_EXT_SSTC))
+		ctx->stimecmp = csr_swap64(CSR_STIMECMP, dom_ctx->stimecmp);
 
 	/* Eager context switch for float */
 	if (sbi_hart_has_extension(scratch, SBI_HART_EXT_F) ||
@@ -206,6 +210,8 @@ static int hart_context_init(u32 hartindex)
 		if (!ctx)
 			return SBI_ENOMEM;
 
+		ctx->stimecmp = ~0ULL;
+
 		if (sbi_hart_has_extension(sbi_scratch_thishart_ptr(),
 					   SBI_HART_EXT_V)) {
 			vec_size = sbi_vector_context_size();
-- 
2.43.0