linux: implement i2c

Signed-off-by:  Eric Callahan <arksine.code@gmail.com>

src/linux/Kconfig

@@ -9,6 +9,7 @@ config LINUX_SELECT
     select HAVE_GPIO_ADC
     select HAVE_GPIO_SPI
     select HAVE_GPIO_HARD_PWM
+    select HAVE_GPIO_I2C
 
 config BOARD_DIRECTORY
     string

src/linux/Makefile

@@ -4,7 +4,7 @@ dirs-y += src/linux src/generic
 
 src-y += linux/main.c linux/timer.c linux/console.c linux/watchdog.c
 src-y += linux/pca9685.c linux/spidev.c linux/analog.c linux/hard_pwm.c
-src-y += generic/crc16_ccitt.c generic/alloc.c
+src-y += linux/i2c.c generic/crc16_ccitt.c generic/alloc.c
 
 CFLAGS_klipper.elf += -lutil
 

src/linux/gpio.h

@@ -35,4 +35,13 @@ struct gpio_pwm {
 struct gpio_pwm gpio_pwm_setup(uint8_t pin, uint32_t cycle_time, uint16_t val);
 void gpio_pwm_write(struct gpio_pwm g, uint16_t val);
 
+struct i2c_config {
+    int fd;
+};
+
+struct i2c_config i2c_setup(uint32_t bus, uint32_t rate, uint8_t addr);
+void i2c_write(struct i2c_config config, uint8_t write_len, uint8_t *write);
+void i2c_read(struct i2c_config config, uint8_t reg_len, uint8_t *reg
+              , uint8_t read_len, uint8_t *read);
+
 #endif // gpio.h

src/linux/i2c.c

@@ -0,0 +1,101 @@
+// Linux i2c implementation
+//
+// Copyright (C) 2020  Eric Callahan <arksine.code@gmail.com>
+//
+// This file may be distributed under the terms of the GNU GPLv3 license.
+#include <fcntl.h> // open
+#include <linux/i2c-dev.h> // I2C_SLAVE
+#include <stdio.h> // snprintf
+#include <sys/ioctl.h> // ioctl
+#include <unistd.h> // write
+#include "gpio.h" // i2c_setup
+#include "command.h" // shutdown
+#include "internal.h" // report_errno
+#include "sched.h" // sched_shutdown
+
+DECL_ENUMERATION_RANGE("i2c_bus", "i2c.0", 0, 2);
+
+struct i2c_s {
+    uint32_t bus;
+    uint8_t addr;
+    int fd;
+};
+
+static struct i2c_s devices[16];
+static int devices_count;
+
+static int
+i2c_open(uint32_t bus, uint8_t addr)
+{
+    // Find existing device (if already opened)
+    int i;
+    for (i=0; i<devices_count; i++) {
+        if (devices[i].bus == bus && devices[i].addr == addr) {
+            return devices[i].fd;
+        }
+    }
+
+    char fname[256];
+    snprintf(fname, sizeof(fname), "/dev/i2c-%d", bus);
+    int fd = open(fname, O_RDWR|O_CLOEXEC);
+    if (fd < 0) {
+        report_errno("open i2c", fd);
+        goto fail;
+    }
+    int ret = ioctl(fd, I2C_SLAVE, addr);
+    if (ret < 0) {
+        report_errno("ioctl i2c", fd);
+        goto fail;
+    }
+    ret = set_non_blocking(fd);
+    if (ret < 0)
+        goto fail;
+
+    devices[devices_count].bus = bus;
+    devices[devices_count].addr = addr;
+    devices[devices_count].fd = fd;
+    devices_count++;
+
+    return fd;
+
+fail:
+    if (fd >= 0)
+        close(fd);
+    shutdown("Unable to open i2c device");
+}
+
+struct i2c_config
+i2c_setup(uint32_t bus, uint32_t rate, uint8_t addr)
+{
+    // Note:  The rate is set by the kernel driver, for a Raspberry Pi this
+    // is done with the following setting in /boot/config.txt:
+    //
+    // dtparam=i2c_baudrate=<rate>
+
+    int fd = i2c_open(bus, addr);
+    return (struct i2c_config){.fd=fd};
+}
+
+void
+i2c_write(struct i2c_config config, uint8_t write_len, uint8_t *data)
+{
+    int ret = write(config.fd, data, write_len);
+    if (ret != write_len) {
+        if (ret < 0)
+            report_errno("write value i2c", ret);
+        try_shutdown("Unable write i2c device");
+    }
+}
+
+void
+i2c_read(struct i2c_config config, uint8_t reg_len, uint8_t *reg
+         , uint8_t read_len, uint8_t *data)
+{
+    i2c_write(config, reg_len, reg);
+    int ret = read(config.fd, data, read_len);
+    if (ret != read_len) {
+        if (ret < 0)
+            report_errno("read value i2c", ret);
+        try_shutdown("Unable to read i2c device");
+    }
+}