lib: sbi: enable seed access in S-mode

If ISA extension Zkr is available, set

    mseccfg.sseed=1
    mseccfg.useed=0

This enables access to the seed CSR in S-mode but not in U-mode.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Anup Patel <anup@brainfault.org>

lib/sbi/sbi_hart.c

@@ -160,6 +160,12 @@ static void mstatus_init(struct sbi_scratch *scratch)
 		}
 
 		csr_write(CSR_MENVCFG, menvcfg_val);
+
+		/* Enable S-mode access to seed CSR */
+		if (sbi_hart_has_extension(scratch, SBI_HART_EXT_ZKR)) {
+			csr_set(CSR_MSECCFG, MSECCFG_SSEED);
+			csr_clear(CSR_MSECCFG, MSECCFG_USEED);
+		}
 	}
 
 	/* Disable all interrupts */