drivers/iio/adc/ep93xx_adc.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * Driver for ADC module on the Cirrus Logic EP93xx series of SoCs
   4  *
   5  * Copyright (C) 2015 Alexander Sverdlin
   6  *
   7  * The driver uses polling to get the conversion status. According to EP93xx
   8  * datasheets, reading ADCResult register starts the conversion, but user is also
   9  * responsible for ensuring that delay between adjacent conversion triggers is
  10  * long enough so that maximum allowed conversion rate is not exceeded. This
  11  * basically renders IRQ mode unusable.
  12  */
  13
  14 #include <linux/clk.h>
  15 #include <linux/delay.h>
  16 #include <linux/device.h>
  17 #include <linux/err.h>
  18 #include <linux/iio/iio.h>
  19 #include <linux/io.h>
  20 #include <linux/irqflags.h>
  21 #include <linux/module.h>
  22 #include <linux/mutex.h>
  23 #include <linux/platform_device.h>
  24 #include <linux/of.h>
  25
  26 /*
  27  * This code could benefit from real HR Timers, but jiffy granularity would
  28  * lower ADC conversion rate down to CONFIG_HZ, so we fallback to busy wait
  29  * in such case.
  30  *
  31  * HR Timers-based version loads CPU only up to 10% during back to back ADC
  32  * conversion, while busy wait-based version consumes whole CPU power.
  33  */
  34 #ifdef CONFIG_HIGH_RES_TIMERS
  35 #define ep93xx_adc_delay(usmin, usmax) usleep_range(usmin, usmax)
  36 #else
  37 #define ep93xx_adc_delay(usmin, usmax) udelay(usmin)
  38 #endif
  39
  40 #define EP93XX_ADC_RESULT       0x08
  41 #define   EP93XX_ADC_SDR        BIT(31)
  42 #define EP93XX_ADC_SWITCH       0x18
  43 #define EP93XX_ADC_SW_LOCK      0x20
  44
  45 struct ep93xx_adc_priv {
  46         struct clk *clk;
  47         void __iomem *base;
  48         int lastch;
  49         struct mutex lock;
  50 };
  51
  52 #define EP93XX_ADC_CH(index, dname, swcfg) {                    \
  53         .type = IIO_VOLTAGE,                                    \
  54         .indexed = 1,                                           \
  55         .channel = index,                                       \
  56         .address = swcfg,                                       \
  57         .datasheet_name = dname,                                \
  58         .info_mask_separate = BIT(IIO_CHAN_INFO_RAW),           \
  59         .info_mask_shared_by_all = BIT(IIO_CHAN_INFO_SCALE) |   \
  60                                    BIT(IIO_CHAN_INFO_OFFSET),   \
  61 }
  62
  63 /*
  64  * Numbering scheme for channels 0..4 is defined in EP9301 and EP9302 datasheets.
  65  * EP9307, EP9312 and EP9312 have 3 channels more (total 8), but the numbering is
  66  * not defined. So the last three are numbered randomly, let's say.
  67  */
  68 static const struct iio_chan_spec ep93xx_adc_channels[8] = {
  69         EP93XX_ADC_CH(0, "YM",  0x608),
  70         EP93XX_ADC_CH(1, "SXP", 0x680),
  71         EP93XX_ADC_CH(2, "SXM", 0x640),
  72         EP93XX_ADC_CH(3, "SYP", 0x620),
  73         EP93XX_ADC_CH(4, "SYM", 0x610),
  74         EP93XX_ADC_CH(5, "XP",  0x601),
  75         EP93XX_ADC_CH(6, "XM",  0x602),
  76         EP93XX_ADC_CH(7, "YP",  0x604),
  77 };
  78
  79 static int ep93xx_read_raw(struct iio_dev *iiodev,
  80                            struct iio_chan_spec const *channel, int *value,
  81                            int *shift, long mask)
  82 {
  83         struct ep93xx_adc_priv *priv = iio_priv(iiodev);
  84         unsigned long timeout;
  85         int ret;
  86
  87         switch (mask) {
  88         case IIO_CHAN_INFO_RAW:
  89                 mutex_lock(&priv->lock);
  90                 if (priv->lastch != channel->channel) {
  91                         priv->lastch = channel->channel;
  92                         /*
  93                          * Switch register is software-locked, unlocking must be
  94                          * immediately followed by write
  95                          */
  96                         local_irq_disable();
  97                         writel_relaxed(0xAA, priv->base + EP93XX_ADC_SW_LOCK);
  98                         writel_relaxed(channel->address,
  99                                        priv->base + EP93XX_ADC_SWITCH);
 100                         local_irq_enable();
 101                         /*
 102                          * Settling delay depends on module clock and could be
 103                          * 2ms or 500us
 104                          */
 105                         ep93xx_adc_delay(2000, 2000);
 106                 }
 107                 /* Start the conversion, eventually discarding old result */
 108                 readl_relaxed(priv->base + EP93XX_ADC_RESULT);
 109                 /* Ensure maximum conversion rate is not exceeded */
 110                 ep93xx_adc_delay(DIV_ROUND_UP(1000000, 925),
 111                                  DIV_ROUND_UP(1000000, 925));
 112                 /* At this point conversion must be completed, but anyway... */
 113                 ret = IIO_VAL_INT;
 114                 timeout = jiffies + msecs_to_jiffies(1) + 1;
 115                 while (1) {
 116                         u32 t;
 117
 118                         t = readl_relaxed(priv->base + EP93XX_ADC_RESULT);
 119                         if (t & EP93XX_ADC_SDR) {
 120                                 *value = sign_extend32(t, 15);
 121                                 break;
 122                         }
 123
 124                         if (time_after(jiffies, timeout)) {
 125                                 dev_err(&iiodev->dev, "Conversion timeout\n");
 126                                 ret = -ETIMEDOUT;
 127                                 break;
 128                         }
 129
 130                         cpu_relax();
 131                 }
 132                 mutex_unlock(&priv->lock);
 133                 return ret;
 134
 135         case IIO_CHAN_INFO_OFFSET:
 136                 /* According to datasheet, range is -25000..25000 */
 137                 *value = 25000;
 138                 return IIO_VAL_INT;
 139
 140         case IIO_CHAN_INFO_SCALE:
 141                 /* Typical supply voltage is 3.3v */
 142                 *value = (1ULL << 32) * 3300 / 50000;
 143                 *shift = 32;
 144                 return IIO_VAL_FRACTIONAL_LOG2;
 145         }
 146
 147         return -EINVAL;
 148 }
 149
 150 static const struct iio_info ep93xx_adc_info = {
 151         .read_raw = ep93xx_read_raw,
 152 };
 153
 154 static int ep93xx_adc_probe(struct platform_device *pdev)
 155 {
 156         int ret;
 157         struct iio_dev *iiodev;
 158         struct ep93xx_adc_priv *priv;
 159         struct clk *pclk;
 160
 161         iiodev = devm_iio_device_alloc(&pdev->dev, sizeof(*priv));
 162         if (!iiodev)
 163                 return -ENOMEM;
 164         priv = iio_priv(iiodev);
 165
 166         priv->base = devm_platform_ioremap_resource(pdev, 0);
 167         if (IS_ERR(priv->base))
 168                 return PTR_ERR(priv->base);
 169
 170         iiodev->name = dev_name(&pdev->dev);
 171         iiodev->modes = INDIO_DIRECT_MODE;
 172         iiodev->info = &ep93xx_adc_info;
 173         iiodev->num_channels = ARRAY_SIZE(ep93xx_adc_channels);
 174         iiodev->channels = ep93xx_adc_channels;
 175
 176         priv->lastch = -1;
 177         mutex_init(&priv->lock);
 178
 179         platform_set_drvdata(pdev, iiodev);
 180
 181         priv->clk = devm_clk_get(&pdev->dev, NULL);
 182         if (IS_ERR(priv->clk)) {
 183                 dev_err(&pdev->dev, "Cannot obtain clock\n");
 184                 return PTR_ERR(priv->clk);
 185         }
 186
 187         pclk = clk_get_parent(priv->clk);
 188         if (!pclk) {
 189                 dev_warn(&pdev->dev, "Cannot obtain parent clock\n");
 190         } else {
 191                 /*
 192                  * This is actually a place for improvement:
 193                  * EP93xx ADC supports two clock divisors -- 4 and 16,
 194                  * resulting in conversion rates 3750 and 925 samples per second
 195                  * with 500us or 2ms settling time respectively.
 196                  * One might find this interesting enough to be configurable.
 197                  */
 198                 ret = clk_set_rate(priv->clk, clk_get_rate(pclk) / 16);
 199                 if (ret)
 200                         dev_warn(&pdev->dev, "Cannot set clock rate\n");
 201                 /*
 202                  * We can tolerate rate setting failure because the module should
 203                  * work in any case.
 204                  */
 205         }
 206
 207         ret = clk_prepare_enable(priv->clk);
 208         if (ret) {
 209                 dev_err(&pdev->dev, "Cannot enable clock\n");
 210                 return ret;
 211         }
 212
 213         ret = iio_device_register(iiodev);
 214         if (ret)
 215                 clk_disable_unprepare(priv->clk);
 216
 217         return ret;
 218 }
 219
 220 static int ep93xx_adc_remove(struct platform_device *pdev)
 221 {
 222         struct iio_dev *iiodev = platform_get_drvdata(pdev);
 223         struct ep93xx_adc_priv *priv = iio_priv(iiodev);
 224
 225         iio_device_unregister(iiodev);
 226         clk_disable_unprepare(priv->clk);
 227
 228         return 0;
 229 }
 230
 231 static const struct of_device_id ep93xx_adc_of_ids[] = {
 232         { .compatible = "cirrus,ep9301-adc" },
 233         {}
 234 };
 235 MODULE_DEVICE_TABLE(of, ep93xx_adc_of_ids);
 236
 237 static struct platform_driver ep93xx_adc_driver = {
 238         .driver = {
 239                 .name = "ep93xx-adc",
 240                 .of_match_table = ep93xx_adc_of_ids,
 241         },
 242         .probe = ep93xx_adc_probe,
 243         .remove = ep93xx_adc_remove,
 244 };
 245 module_platform_driver(ep93xx_adc_driver);
 246
 247 MODULE_AUTHOR("Alexander Sverdlin <alexander.sverdlin@gmail.com>");
 248 MODULE_DESCRIPTION("Cirrus Logic EP93XX ADC driver");
 249 MODULE_LICENSE("GPL");
 250 MODULE_ALIAS("platform:ep93xx-adc");