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Re: [Qemu-devel] [PATCH] tmp105: read temperature in milli-celsius


From: Paolo Bonzini
Subject: Re: [Qemu-devel] [PATCH] tmp105: read temperature in milli-celsius
Date: Mon, 24 Mar 2014 11:09:35 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.3.0

Il 17/02/2014 13:08, Andreas Färber ha scritto:
Am 17.02.2014 11:57, schrieb Paolo Bonzini:
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 <address@hidden>
---
 hw/misc/tmp105.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/hw/misc/tmp105.c b/hw/misc/tmp105.c
index 155e03d..63aa3d6 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;

Hmm, I'll have to check history, but I guess the setter was there and I
wrongly added the getter. That would be easier to ack of course if I
didn't have to think about a complete new formula in both places... ;)


     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);

Did you check whether those magic 4 bits shift were for some other
purpose such as flags possibly? CC'ing Alex Horn.

Since we do have a tmp105-test, we should also add a regression test for
the getter bug.

This is quite hard to do because the tmp105 is under /machine/unattached and thus does not have a stable QOM path. The other way to test it would be to add a libqos driver for the i386 smbus device, add tmp105 to qemu-system-x86_64, and write another tmp105 test.

Given this, is this patch okay for 2.0?

Paolo




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