Introduce a function pointer for sbi_set_timer(), since different OpenSBI
versions may implement the TIME extension with different extension IDs
and/or function IDs.

If the TIME extension is not available, fall back to the legacy timer
mechanism. This is useful when Xen runs as a guest under another Xen,
because the TIME extension is not currently virtualised and therefore
will not appear as available.

The sbi_set_timer() pointer will be used by reprogram_timer() to program
Xen’s physical timer as without SSTC extension there is no any other
option except SBI call to do that as only M-timer is available for us.

Signed-off-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>
---
Changes in v2:
 - Move up defintion of SBI_EXT_TIME_SET_TIMER and use the same padding as
   defintions around it.
 - Add an extra comment about stime_value granuality above declaration of
   sbi_set_timer function pointer.
 - Refactor implemetation of sbi_set_timer_v02().
 - Provide fallback for sbi_set_timer_v01().
 - Update the commit message.
---
 xen/arch/riscv/include/asm/sbi.h | 18 ++++++++++++++
 xen/arch/riscv/sbi.c             | 40 ++++++++++++++++++++++++++++++++
 2 files changed, 58 insertions(+)

diff --git a/xen/arch/riscv/include/asm/sbi.h b/xen/arch/riscv/include/asm/sbi.h
index 79f7ff5c5501..e0e31d7afa20 100644
--- a/xen/arch/riscv/include/asm/sbi.h
+++ b/xen/arch/riscv/include/asm/sbi.h
@@ -29,6 +29,10 @@
 
 #define SBI_EXT_BASE                    0x10
 #define SBI_EXT_RFENCE                  0x52464E43
+#define SBI_EXT_TIME                    0x54494D45
+
+/* SBI function IDs for TIME extension */
+#define SBI_EXT_TIME_SET_TIMER          0x0
 
 /* SBI function IDs for BASE extension */
 #define SBI_EXT_BASE_GET_SPEC_VERSION   0x0
@@ -134,6 +138,20 @@ int sbi_remote_hfence_gvma(const cpumask_t *cpu_mask, vaddr_t start,
 int sbi_remote_hfence_gvma_vmid(const cpumask_t *cpu_mask, vaddr_t start,
                                 size_t size, unsigned long vmid);
 
+/*
+ * Programs the clock for next event after stime_value time. This function also
+ * clears the pending timer interrupt bit.
+ * If the supervisor wishes to clear the timer interrupt without scheduling the
+ * next timer event, it can either request a timer interrupt infinitely far
+ * into the future (i.e., (uint64_t)-1), or it can instead mask the timer
+ * interrupt by clearing sie.STIE CSR bit.
+ * The stime_value parameter represents absolute time measured in ticks.
+ *
+ * This SBI call returns 0 upon success or an implementation specific negative
+ * error code.
+ */
+extern int (*sbi_set_timer)(uint64_t stime_value);
+
 /*
  * Initialize SBI library
  *
diff --git a/xen/arch/riscv/sbi.c b/xen/arch/riscv/sbi.c
index 425dce44c679..2c7757c8839f 100644
--- a/xen/arch/riscv/sbi.c
+++ b/xen/arch/riscv/sbi.c
@@ -249,6 +249,38 @@ static int (* __ro_after_init sbi_rfence)(unsigned long fid,
                                           unsigned long arg4,
                                           unsigned long arg5);
 
+static int cf_check sbi_set_timer_v02(uint64_t stime_value)
+{
+    struct sbiret ret;
+
+    ret = sbi_ecall(SBI_EXT_TIME, SBI_EXT_TIME_SET_TIMER, stime_value,
+#ifdef CONFIG_RISCV_32
+                    stime_value >> 32,
+#else
+                    0,
+#endif
+                    0, 0, 0, 0);
+
+    return sbi_err_map_xen_errno(ret.error);
+}
+
+static int cf_check sbi_set_timer_v01(uint64_t stime_value)
+{
+    struct sbiret ret;
+
+    ret = sbi_ecall(SBI_EXT_0_1_SET_TIMER, 0, stime_value,
+#ifdef CONFIG_RISCV_32
+                    stime_value >> 32,
+#else
+                    0,
+#endif
+                    0, 0, 0, 0);
+
+    return sbi_err_map_xen_errno(ret.error);
+}
+
+int (* __ro_after_init sbi_set_timer)(uint64_t stime_value);
+
 int sbi_remote_sfence_vma(const cpumask_t *cpu_mask, vaddr_t start,
                           size_t size)
 {
@@ -326,6 +358,14 @@ int __init sbi_init(void)
             sbi_rfence = sbi_rfence_v02;
             printk("SBI v0.2 RFENCE extension detected\n");
         }
+
+        if ( sbi_probe_extension(SBI_EXT_TIME) > 0 )
+        {
+            sbi_set_timer = sbi_set_timer_v02;
+            printk("SBI v0.2 TIME extension detected\n");
+        }
+        else
+            sbi_set_timer = sbi_set_timer_v01;
     }
     else
         panic("Ooops. SBI spec version 0.1 detected. Need to add support");
-- 
2.52.0