bsps: Add a GPIO based SPI driver

The driver uses simple pin set or get functions to emulate an SPI. It
doesn't care much for speed settings and just tries it's best.

bsps/shared/dev/spi/spi-gpio.c

@@ -0,0 +1,225 @@
+/* SPDX-License-Identifier: BSD-2-Clause */
+
+/**
+ * @file
+ *
+ * @ingroup RTEMSDeviceSPIGPIO
+ *
+ * @brief This file provides the implementation of @ref RTEMSDeviceSPIGPIO.
+ */
+
+/*
+ * Copyright (C) 2024 embedded brains GmbH & Co. KG
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <bsp.h>
+#include <dev/spi/spi.h>
+#include <dev/spi/spi-gpio.h>
+
+struct spi_gpio_bus {
+  spi_bus base;
+  const struct spi_gpio_params *p;
+};
+
+static int spi_gpio_check_msg(
+  struct spi_gpio_bus *bus,
+  const spi_ioc_transfer *msg
+)
+{
+  /*
+   * Check that only implemented modes are requested.
+   *
+   * Ignore the frequency. This driver doesn't give any guarantees regarding
+   * that.
+   */
+  if ((msg->mode & ~(SPI_CPHA | SPI_CPOL | SPI_NO_CS)) != 0 ||
+      (msg->bits_per_word != 8) ||
+      (msg->delay_usecs != 0) ||
+      (msg->cs >= SPI_GPIO_MAX_CS) ||
+      (bus->p->set_cs[msg->cs] == NULL)) {
+    return -EINVAL;
+  }
+
+  return 0;
+}
+
+static int spi_gpio_transfer_msg(
+  struct spi_gpio_bus *bus,
+  const spi_ioc_transfer *msg
+)
+{
+  uint8_t cs = msg->cs;
+  bool clk_idle = ((msg->mode & SPI_CPOL) != 0);
+  bool cpha = ((msg->mode & SPI_CPHA) != 0);
+  const uint8_t *tx_buf = msg->tx_buf;
+  uint8_t *rx_buf = msg->rx_buf;
+  size_t len = msg->len;
+  int i;
+  int rv;
+
+  rv = spi_gpio_check_msg(bus, msg);
+  if (rv != 0) {
+    return rv;
+  }
+
+  /*
+   * Make sure that all chip selects but the one in the message are idle.
+   * Excluding the one in the message is necessary to avoid deselecting the chip
+   * between messages.
+   */
+  for (i = 0; i < SPI_GPIO_MAX_CS; ++i) {
+    if (i != cs && bus->p->set_cs[i] != NULL) {
+      bus->p->set_cs[i](bus->p->set_cs_arg[i], bus->p->cs_idle[i]);
+    }
+  }
+
+  /* Set up clock according to CPOL. */
+  bus->p->set_clk(bus->p->set_clk_arg, clk_idle);
+
+  /* Now select the chip (if it isn't selected from the previous message) */
+  bus->p->set_cs[cs](bus->p->set_cs_arg[cs], !bus->p->cs_idle[cs]);
+
+  while (len > 0) {
+    uint8_t out = 0xff;
+    uint8_t in = 0;
+    size_t ctr;
+
+    --len;
+
+    if (tx_buf != NULL) {
+      out = *tx_buf;
+      ++tx_buf;
+    }
+
+    /*
+     * Read / Write the data.
+     *
+     * If CPHA=0: Set up data. Read data. Clock to active. Clock to inactive.
+     * If CPHA=1: Clock to active. Set up data. Read data. Clock to inactive.
+     */
+    for (ctr = 0; ctr < sizeof(out) * 8; ++ctr) {
+      bool d_out;
+      bool d_in;
+
+      if (cpha) {
+        bus->p->set_clk(bus->p->set_clk_arg, !clk_idle);
+      }
+
+      d_out = ((out & 0x80) != 0);
+      out <<= 1;
+      bus->p->set_mosi(bus->p->set_mosi_arg, d_out);
+
+      d_in = bus->p->get_miso(bus->p->get_miso_arg);
+      in = (in << 1) | (d_in ? 1 : 0);
+
+      if (!cpha) {
+        bus->p->set_clk(bus->p->set_clk_arg, !clk_idle);
+      }
+      bus->p->set_clk(bus->p->set_clk_arg, clk_idle);
+    }
+
+    if (rx_buf != NULL) {
+      *rx_buf = in;
+      ++rx_buf;
+    }
+  }
+
+  /* Deselect the chip if the message wants that. */
+  if (msg->cs_change) {
+    bus->p->set_cs[cs](bus->p->set_cs_arg[cs], bus->p->cs_idle[cs]);
+  }
+
+  return 0;
+}
+
+static int spi_gpio_transfer(
+  spi_bus *base,
+  const spi_ioc_transfer *msgs,
+  uint32_t n
+)
+{
+  struct spi_gpio_bus *bus;
+  bus = (struct spi_gpio_bus *) base;
+  int rv = 0;
+
+  while (n > 0 && rv == 0) {
+    rv = spi_gpio_transfer_msg(bus, msgs);
+    --n;
+    ++msgs;
+  };
+
+  return rv;
+}
+
+static void spi_gpio_destroy(spi_bus *base)
+{
+  struct spi_gpio_bus *bus;
+  bus = (struct spi_gpio_bus *) base;
+  spi_bus_destroy_and_free(&bus->base);
+}
+
+static int spi_gpio_setup(spi_bus *base)
+{
+  struct spi_gpio_bus *bus;
+  bus = (struct spi_gpio_bus *) base;
+  struct spi_ioc_transfer msg = {
+    .speed_hz = base->speed_hz,
+    .delay_usecs = base->delay_usecs,
+    .bits_per_word = base->bits_per_word,
+    .mode = base->mode,
+    .cs = base->cs,
+  };
+
+  return spi_gpio_check_msg(bus, &msg);
+}
+
+rtems_status_code
+spi_gpio_init(const char* device, const struct spi_gpio_params *params)
+{
+  struct spi_gpio_bus *bus;
+  int eno;
+
+  if (device == NULL || params == NULL) {
+    return RTEMS_INVALID_ADDRESS;
+  }
+
+  bus = (struct spi_gpio_bus*) spi_bus_alloc_and_init(sizeof(*bus));
+  if (bus == NULL) {
+    return RTEMS_UNSATISFIED;
+  }
+
+  bus->p = params;
+
+  bus->base.transfer = spi_gpio_transfer;
+  bus->base.destroy = spi_gpio_destroy;
+  bus->base.setup = spi_gpio_setup;
+
+  eno = spi_bus_register(&bus->base, device);
+  if (eno != 0) {
+    spi_bus_destroy_and_free(&bus->base);
+    return RTEMS_UNSATISFIED;
+  }
+
+  return RTEMS_SUCCESSFUL;
+}