drivers/thermal/tango_thermal.c

   1 #include <linux/io.h>
   2 #include <linux/delay.h>
   3 #include <linux/module.h>
   4 #include <linux/thermal.h>
   5 #include <linux/platform_device.h>
   6
   7 /*
   8  * According to a data sheet draft, "this temperature sensor uses a bandgap
   9  * type of circuit to compare a voltage which has a negative temperature
  10  * coefficient with a voltage that is proportional to absolute temperature.
  11  * A resistor bank allows 41 different temperature thresholds to be selected
  12  * and the logic output will then indicate whether the actual die temperature
  13  * lies above or below the selected threshold."
  14  */
  15
  16 #define TEMPSI_CMD      0
  17 #define TEMPSI_RES      4
  18 #define TEMPSI_CFG      8
  19
  20 #define CMD_OFF         0
  21 #define CMD_ON          1
  22 #define CMD_READ        2
  23
  24 #define IDX_MIN         15
  25 #define IDX_MAX         40
  26
  27 struct tango_thermal_priv {
  28         void __iomem *base;
  29         int thresh_idx;
  30 };
  31
  32 static bool temp_above_thresh(void __iomem *base, int thresh_idx)
  33 {
  34         writel(CMD_READ | thresh_idx << 8, base + TEMPSI_CMD);
  35         usleep_range(10, 20);
  36         writel(CMD_READ | thresh_idx << 8, base + TEMPSI_CMD);
  37
  38         return readl(base + TEMPSI_RES);
  39 }
  40
  41 static int tango_get_temp(void *arg, int *res)
  42 {
  43         struct tango_thermal_priv *priv = arg;
  44         int idx = priv->thresh_idx;
  45
  46         if (temp_above_thresh(priv->base, idx)) {
  47                 /* Search upward by incrementing thresh_idx */
  48                 while (idx < IDX_MAX && temp_above_thresh(priv->base, ++idx))
  49                         cpu_relax();
  50                 idx = idx - 1; /* always return lower bound */
  51         } else {
  52                 /* Search downward by decrementing thresh_idx */
  53                 while (idx > IDX_MIN && !temp_above_thresh(priv->base, --idx))
  54                         cpu_relax();
  55         }
  56
  57         *res = (idx * 9 / 2 - 38) * 1000; /* millidegrees Celsius */
  58         priv->thresh_idx = idx;
  59
  60         return 0;
  61 }
  62
  63 static const struct thermal_zone_of_device_ops ops = {
  64         .get_temp       = tango_get_temp,
  65 };
  66
  67 static int tango_thermal_probe(struct platform_device *pdev)
  68 {
  69         struct resource *res;
  70         struct tango_thermal_priv *priv;
  71         struct thermal_zone_device *tzdev;
  72
  73         priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
  74         if (!priv)
  75                 return -ENOMEM;
  76
  77         res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
  78         priv->base = devm_ioremap_resource(&pdev->dev, res);
  79         if (IS_ERR(priv->base))
  80                 return PTR_ERR(priv->base);
  81
  82         priv->thresh_idx = IDX_MIN;
  83         writel(0, priv->base + TEMPSI_CFG);
  84         writel(CMD_ON, priv->base + TEMPSI_CMD);
  85
  86         tzdev = devm_thermal_zone_of_sensor_register(&pdev->dev, 0, priv, &ops);
  87         return PTR_ERR_OR_ZERO(tzdev);
  88 }
  89
  90 static const struct of_device_id tango_sensor_ids[] = {
  91         {
  92                 .compatible = "sigma,smp8758-thermal",
  93         },
  94         { /* sentinel */ }
  95 };
  96
  97 static struct platform_driver tango_thermal_driver = {
  98         .probe  = tango_thermal_probe,
  99         .driver = {
 100                 .name           = "tango-thermal",
 101                 .of_match_table = tango_sensor_ids,
 102         },
 103 };
 104
 105 module_platform_driver(tango_thermal_driver);
 106
 107 MODULE_LICENSE("GPL");
 108 MODULE_AUTHOR("Sigma Designs");
 109 MODULE_DESCRIPTION("Tango temperature sensor");