xen/riscv: introduce sbi_set_timer()

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.
Despite of the fact that sbi_set_timer_v01 is introduced and used as
fall back, SBI v0.1 still isn't fully supported (with the current SBI
calls usage, sbi_rfence_v01 should be introduced too), so panic()
in sbi_init() isn't removed.

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.

Use dprintk() for all the cases to print that a speicifc SBI extension
is available as it isn't really necessary in case of release builds.

Signed-off-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>
Acked-by: Jan Beulich <jbeulich@suse.com>

xen/arch/riscv/include/asm/sbi.h

@@ -13,6 +13,7 @@
 #define ASM__RISCV__SBI_H
 
 #include <xen/cpumask.h>
+#include <xen/sections.h>
 
 /* SBI-defined implementation ID */
 #define SBI_XEN_IMPID 7
@@ -29,6 +30,7 @@
 
 #define SBI_EXT_BASE                    0x10
 #define SBI_EXT_RFENCE                  0x52464E43
+#define SBI_EXT_TIME                    0x54494D45
 
 /* SBI function IDs for BASE extension */
 #define SBI_EXT_BASE_GET_SPEC_VERSION   0x0
@@ -48,6 +50,9 @@
 #define SBI_EXT_RFENCE_REMOTE_HFENCE_VVMA       0x5
 #define SBI_EXT_RFENCE_REMOTE_HFENCE_VVMA_ASID  0x6
 
+/* SBI function IDs for TIME extension */
+#define SBI_EXT_TIME_SET_TIMER          0x0
+
 #define SBI_SPEC_VERSION_MAJOR_MASK     0x7f000000
 #define SBI_SPEC_VERSION_MINOR_MASK     0x00ffffff
 
@@ -134,6 +139,23 @@ 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 at (or after) stime_value. stime_value is
+ * in absolute time. This function must clear the pending timer interrupt bit
+ * as well.
+ *
+ * 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 (* __ro_after_init sbi_set_timer)(uint64_t stime_value);
+
 /*
  * Initialize SBI library
  *

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) = sbi_set_timer_v01;
+
 int sbi_remote_sfence_vma(const cpumask_t *cpu_mask, vaddr_t start,
                           size_t size)
 {
@@ -324,7 +356,13 @@ int __init sbi_init(void)
         if ( sbi_probe_extension(SBI_EXT_RFENCE) > 0 )
         {
             sbi_rfence = sbi_rfence_v02;
-            printk("SBI v0.2 RFENCE extension detected\n");
+            dprintk(XENLOG_INFO, "SBI v0.2 RFENCE extension detected\n");
+        }
+
+        if ( sbi_probe_extension(SBI_EXT_TIME) > 0 )
+        {
+            sbi_set_timer = sbi_set_timer_v02;
+            dprintk(XENLOG_INFO, "SBI v0.2 TIME extension detected\n");
         }
     }
     else