efi_loader: correctly implement 100ns conversion

In efi_set_timer we receive the trigger time in intervals of 100 ns.
We should convert it to intervals of 1000 ns by 64bit division.

The patch supplies function efi_div10 that uses multiplication to
implement the missing 64 bit division.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Alexander Graf <agraf@suse.de>

diff --git a/lib/efi_loader/efi_boottime.c b/lib/efi_loader/efi_boottime.c
index b8dfceae0c003b529c16e3449f3532d3def93a16..a89a62940624e7021562c2b8212b65c63d0fde21 100644 (file)
--- a/lib/efi_loader/efi_boottime.c
+++ b/lib/efi_loader/efi_boottime.c
@@ -81,6 +81,39 @@ efi_status_t efi_exit_func(efi_status_t ret)
        return ret;
 }
 
+/* Low 32 bit */
+#define EFI_LOW32(a) (a & 0xFFFFFFFFULL)
+/* High 32 bit */
+#define EFI_HIGH32(a) (a >> 32)
+
+/*
+ * 64bit division by 10 implemented as multiplication by 1 / 10
+ *
+ * Decimals of one tenth: 0x1 / 0xA = 0x0.19999...
+ */
+#define EFI_TENTH 0x199999999999999A
+static u64 efi_div10(u64 a)
+{
+       u64 prod;
+       u64 rem;
+       u64 ret;
+
+       ret  = EFI_HIGH32(a) * EFI_HIGH32(EFI_TENTH);
+       prod = EFI_HIGH32(a) * EFI_LOW32(EFI_TENTH);
+       rem  = EFI_LOW32(prod);
+       ret += EFI_HIGH32(prod);
+       prod = EFI_LOW32(a) * EFI_HIGH32(EFI_TENTH);
+       rem += EFI_LOW32(prod);
+       ret += EFI_HIGH32(prod);
+       prod = EFI_LOW32(a) * EFI_LOW32(EFI_TENTH);
+       rem += EFI_HIGH32(prod);
+       ret += EFI_HIGH32(rem);
+       /* Round to nearest integer */
+       if (rem >= (1 << 31))
+               ++ret;
+       return ret;
+}
+
 void efi_signal_event(struct efi_event *event)
 {
        if (event->signaled)
@@ -244,7 +277,7 @@ void efi_timer_check(void)
                        continue;
                if (efi_events[i].trigger_type == EFI_TIMER_PERIODIC) {
                        efi_events[i].trigger_next +=
-                               efi_events[i].trigger_time / 10;
+                               efi_events[i].trigger_time;
                        efi_events[i].signaled = 0;
                }
                efi_signal_event(&efi_events[i]);
@@ -255,15 +288,13 @@ void efi_timer_check(void)
 efi_status_t efi_set_timer(struct efi_event *event, int type,
                           uint64_t trigger_time)
 {
-       /* We don't have 64bit division available everywhere, so limit timer
-        * distances to 32bit bits. */
-       u32 trigger32 = trigger_time;
        int i;
 
-       if (trigger32 < trigger_time) {
-               printf("WARNING: Truncating timer from %"PRIx64" to %x\n",
-                      trigger_time, trigger32);
-       }
+       /*
+        * The parameter defines a multiple of 100ns.
+        * We use multiples of 1000ns. So divide by 10.
+        */
+       trigger_time = efi_div10(trigger_time);
 
        for (i = 0; i < ARRAY_SIZE(efi_events); ++i) {
                if (event != &efi_events[i])
@@ -278,7 +309,7 @@ efi_status_t efi_set_timer(struct efi_event *event, int type,
                case EFI_TIMER_PERIODIC:
                case EFI_TIMER_RELATIVE:
                        event->trigger_next =
-                               timer_get_us() + (trigger32 / 10);
+                               timer_get_us() + trigger_time;
                        break;
                default:
                        return EFI_INVALID_PARAMETER;