tmp105: Read temperature in milli-celsius

Right now, the temperature property must be written in milli-celsius,
but it reads back the value in 8.8 fixed point.  Fix this by letting the
property read back the original value (possibly rounded).  Also simplify
the code that does the conversion.

Before:

    (QEMU) qom-set path=/machine/peripheral/sensor property=temperature value=20000
    {u'return': {}}
    (QEMU) qom-get path=sensor property=temperature
    {u'return': 5120}

After:

    (QEMU) qom-set path=/machine/peripheral/sensor property=temperature value=20000
    {u'return': {}}
    (QEMU) qom-get path=sensor property=temperature
    {u'return': 20000}

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>

1 files changed, 5 insertions, 3 deletions

diff --git a/hw/misc/tmp105.c b/hw/misc/tmp105.c
index 155e03df80..63aa3d6277 100644
--- a/hw/misc/tmp105.c
+++ b/hw/misc/tmp105.c
@@ -56,12 +56,14 @@ static void tmp105_get_temperature(Object *obj, Visitor *v, void *opaque,
                                    const char *name, Error **errp)
 {
     TMP105State *s = TMP105(obj);
-    int64_t value = s->temperature;
+    int64_t value = s->temperature * 1000 / 256;
 
     visit_type_int(v, &value, name, errp);
 }
 
-/* Units are 0.001 centigrades relative to 0 C.  */
+/* Units are 0.001 centigrades relative to 0 C.  s->temperature is 8.8
+ * fixed point, so units are 1/256 centigrades.  A simple ratio will do.
+ */
 static void tmp105_set_temperature(Object *obj, Visitor *v, void *opaque,
                                    const char *name, Error **errp)
 {
@@ -78,7 +80,7 @@ static void tmp105_set_temperature(Object *obj, Visitor *v, void *opaque,
         return;
     }
 
-    s->temperature = ((int16_t) (temp * 0x800 / 128000)) << 4;
+    s->temperature = (int16_t) (temp * 256 / 1000);
 
     tmp105_alarm_update(s);
 }