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From: Peter Maydell <peter.maydell@linaro.org>
To: qemu-devel@nongnu.org
Subject: [PULL 9/9] tmp105: Correct handling of temperature limit checks
Date: Tue, 17 Nov 2020 13:48:34 +0000
Message-Id: <20201117134834.31731-10-peter.maydell@linaro.org>
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The TMP105 datasheet says that in Interrupt Mode (when TM=3D=3D1) the device
signals an alert when the temperature equals or exceeds the T_high value and
then remains high until a device register is read or the device responds to
the SMBUS Alert Response address, or the device is put into Shutdown Mode.
Thereafter the Alert pin will only be re-signalled when temperature falls
below T_low; alert can then be cleared in the same set of ways, and the
device returns to its initial "alert when temperature goes above T_high"
mode. (If this textual description is confusing, see figure 3 in the
TI datasheet at https://www.ti.com/lit/gpn/tmp105 .)
We were misimplementing this as a simple "always alert if temperature is
above T_high or below T_low" condition, which gives a spurious alert on
startup if using the "T_high =3D 80 degrees C, T_low =3D 75 degrees C" reset
limit values.
Implement the correct (hysteresis) behaviour by tracking whether we
are currently looking for the temperature to rise over T_high or
for it to fall below T_low. Our implementation of the comparator
mode (TM=3D=3D0) wasn't wrong, but rephrase it to match the way that
interrupt mode is now handled for clarity.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: C=C3=A9dric Le Goater <clg@kaod.org>
Message-id: 20201110150023.25533-3-peter.maydell@linaro.org
---
hw/misc/tmp105.h | 7 +++++
hw/misc/tmp105.c | 70 +++++++++++++++++++++++++++++++++++++++++-------
2 files changed, 68 insertions(+), 9 deletions(-)
diff --git a/hw/misc/tmp105.h b/hw/misc/tmp105.h
index e5198fce80a..7c97071ad75 100644
--- a/hw/misc/tmp105.h
+++ b/hw/misc/tmp105.h
@@ -43,6 +43,13 @@ struct TMP105State {
int16_t limit[2];
int faults;
uint8_t alarm;
+ /*
+ * The TMP105 initially looks for a temperature rising above T_high;
+ * once this is detected, the condition it looks for next is the
+ * temperature falling below T_low. This flag is false when initially
+ * looking for T_high, true when looking for T_low.
+ */
+ bool detect_falling;
};
=20
#endif
diff --git a/hw/misc/tmp105.c b/hw/misc/tmp105.c
index 0a4aad4854e..d299d9b21b7 100644
--- a/hw/misc/tmp105.c
+++ b/hw/misc/tmp105.c
@@ -41,16 +41,40 @@ static void tmp105_alarm_update(TMP105State *s)
return;
}
=20
- if ((s->config >> 1) & 1) { /* TM */
- if (s->temperature >=3D s->limit[1])
- s->alarm =3D 1;
- else if (s->temperature < s->limit[0])
- s->alarm =3D 1;
+ if (s->config >> 1 & 1) {
+ /*
+ * TM =3D=3D 1 : Interrupt mode. We signal Alert when the
+ * temperature rises above T_high, and expect the guest to clear
+ * it (eg by reading a device register).
+ */
+ if (s->detect_falling) {
+ if (s->temperature < s->limit[0]) {
+ s->alarm =3D 1;
+ s->detect_falling =3D false;
+ }
+ } else {
+ if (s->temperature >=3D s->limit[1]) {
+ s->alarm =3D 1;
+ s->detect_falling =3D true;
+ }
+ }
} else {
- if (s->temperature >=3D s->limit[1])
- s->alarm =3D 1;
- else if (s->temperature < s->limit[0])
- s->alarm =3D 0;
+ /*
+ * TM =3D=3D 0 : Comparator mode. We signal Alert when the tempera=
ture
+ * rises above T_high, and stop signalling it when the temperature
+ * falls below T_low.
+ */
+ if (s->detect_falling) {
+ if (s->temperature < s->limit[0]) {
+ s->alarm =3D 0;
+ s->detect_falling =3D false;
+ }
+ } else {
+ if (s->temperature >=3D s->limit[1]) {
+ s->alarm =3D 1;
+ s->detect_falling =3D true;
+ }
+ }
}
=20
tmp105_interrupt_update(s);
@@ -197,6 +221,29 @@ static int tmp105_post_load(void *opaque, int version_=
id)
return 0;
}
=20
+static bool detect_falling_needed(void *opaque)
+{
+ TMP105State *s =3D opaque;
+
+ /*
+ * We only need to migrate the detect_falling bool if it's set;
+ * for migration from older machines we assume that it is false
+ * (ie temperature is not out of range).
+ */
+ return s->detect_falling;
+}
+
+static const VMStateDescription vmstate_tmp105_detect_falling =3D {
+ .name =3D "TMP105/detect-falling",
+ .version_id =3D 1,
+ .minimum_version_id =3D 1,
+ .needed =3D detect_falling_needed,
+ .fields =3D (VMStateField[]) {
+ VMSTATE_BOOL(detect_falling, TMP105State),
+ VMSTATE_END_OF_LIST()
+ }
+};
+
static const VMStateDescription vmstate_tmp105 =3D {
.name =3D "TMP105",
.version_id =3D 0,
@@ -212,6 +259,10 @@ static const VMStateDescription vmstate_tmp105 =3D {
VMSTATE_UINT8(alarm, TMP105State),
VMSTATE_I2C_SLAVE(i2c, TMP105State),
VMSTATE_END_OF_LIST()
+ },
+ .subsections =3D (const VMStateDescription*[]) {
+ &vmstate_tmp105_detect_falling,
+ NULL
}
};
=20
@@ -224,6 +275,7 @@ static void tmp105_reset(I2CSlave *i2c)
s->config =3D 0;
s->faults =3D tmp105_faultq[(s->config >> 3) & 3];
s->alarm =3D 0;
+ s->detect_falling =3D false;
=20
s->limit[0] =3D 0x4b00; /* T_LOW, 75 degrees C */
s->limit[1] =3D 0x5000; /* T_HIGH, 80 degrees C */
--=20
2.20.1