thermal: add temperature sensor support for tango SoC

The Tango thermal driver provides support for the primitive temperature
sensor embedded in Tango chips since the SMP8758.

This sensor only generates a 1-bit signal to indicate whether the die
temperature exceeds a programmable threshold.

Signed-off-by: Marc Gonzalez <marc_gonzalez@sigmadesigns.com>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>

1 files changed, 111 insertions, 0 deletions

diff --git a/drivers/thermal/tango_thermal.c b/drivers/thermal/tango_thermal.c
new file mode 100644
index 000000000000..d6592bfbd057
--- /dev/null
+++ b/drivers/thermal/tango_thermal.c
@@ -0,0 +1,111 @@
+#include <linux/io.h>
+#include <linux/delay.h>
+#include <linux/module.h>
+#include <linux/thermal.h>
+#include <linux/platform_device.h>
+
+/*
+ * According to a data sheet draft, "this temperature sensor uses a bandgap
+ * type of circuit to compare a voltage which has a negative temperature
+ * coefficient with a voltage that is proportional to absolute temperature.
+ * A resistor bank allows 41 different temperature thresholds to be selected
+ * and the logic output will then indicate whether the actual die temperature
+ * lies above or below the selected threshold."
+ */
+
+#define TEMPSI_CMD      0
+#define TEMPSI_RES      4
+#define TEMPSI_CFG      8
+
+#define CMD_OFF         0
+#define CMD_ON          1
+#define CMD_READ        2
+
+#define IDX_MIN         15
+#define IDX_MAX         40
+
+struct tango_thermal_priv {
+        void __iomem *base;
+        int thresh_idx;
+};
+
+static bool temp_above_thresh(void __iomem *base, int thresh_idx)
+{
+        writel(CMD_READ | thresh_idx << 8, base + TEMPSI_CMD);
+        usleep_range(10, 20);
+        writel(CMD_READ | thresh_idx << 8, base + TEMPSI_CMD);
+
+        return readl(base + TEMPSI_RES);
+}
+
+static int tango_get_temp(void *arg, int *res)
+{
+        struct tango_thermal_priv *priv = arg;
+        int idx = priv->thresh_idx;
+
+        if (temp_above_thresh(priv->base, idx)) {
+                /* Search upward by incrementing thresh_idx */
+                while (idx < IDX_MAX && temp_above_thresh(priv->base, ++idx))
+                        cpu_relax();
+                idx = idx - 1; /* always return lower bound */
+        } else {
+                /* Search downward by decrementing thresh_idx */
+                while (idx > IDX_MIN && !temp_above_thresh(priv->base, --idx))
+                        cpu_relax();
+        }
+
+        *res = (idx * 9 / 2 - 38) * 1000; /* millidegrees Celsius */
+        priv->thresh_idx = idx;
+
+        return 0;
+}
+
+static const struct thermal_zone_of_device_ops ops = {
+        .get_temp       = tango_get_temp,
+};
+
+static int tango_thermal_probe(struct platform_device *pdev)
+{
+        struct resource *res;
+        struct tango_thermal_priv *priv;
+        struct thermal_zone_device *tzdev;
+
+        priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
+        if (!priv)
+                return -ENOMEM;
+
+        res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+        priv->base = devm_ioremap_resource(&pdev->dev, res);
+        if (IS_ERR(priv->base))
+                return PTR_ERR(priv->base);
+
+        priv->thresh_idx = IDX_MIN;
+        writel(CMD_ON, priv->base + TEMPSI_CMD);
+
+        tzdev = devm_thermal_zone_of_sensor_register(&pdev->dev, 0, priv, &ops);
+        if (IS_ERR(tzdev))
+                return PTR_ERR(tzdev);
+
+        return 0;
+}
+
+static const struct of_device_id tango_sensor_ids[] = {
+        {
+                .compatible = "sigma,smp8758-thermal",
+        },
+        { /* sentinel */ }
+};
+
+static struct platform_driver tango_thermal_driver = {
+        .probe  = tango_thermal_probe,
+        .driver = {
+                .name           = "tango-thermal",
+                .of_match_table = tango_sensor_ids,
+        },
+};
+
+module_platform_driver(tango_thermal_driver);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Sigma Designs");
+MODULE_DESCRIPTION("Tango temperature sensor");