bsps/shared: Add MCP7940M RTC driver

The MCP7940M is a I2C RTC chip. The new driver uses the dev/i2c API to
support the RTC. It is written with the intention, that the driver can
be adapted to other RTCs with a similar register layout by just
replacing the initialization function.

bsps/include/libchip/mcp7940m-rtc.h

@@ -0,0 +1,103 @@
+/* SPDX-License-Identifier: BSD-2-Clause */
+
+/*
+ * Copyright (C) 2023 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.
+ */
+
+#ifndef LIBCHIP_MCP7940M_RTC_H
+#define LIBCHIP_MCP7940M_RTC_H
+
+#include <rtems.h>
+#include <rtems/thread.h>
+#include <libchip/rtc.h>
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif /* __cplusplus */
+
+extern const rtc_fns rtc_mcp7940m_fns;
+bool rtc_mcp7940m_probe(int minor);
+
+/*
+ * It is expected, that the RTC can be accessed as a raw file. A pointer to a
+ * constant string with the name of that device has to be passed to the table
+ * initializer.
+ *
+ * The MCP7940M uses an EEPROM-like interface. So you could for example use the
+ * following initialization:
+ *
+ * Define a context for the RTC somewhere:
+ *
+ *   static struct mcp7940m_rtc rtc_ctx =
+ *     MCP7940M_RTC_INITIALIZER("/dev/i2c-1", 0x6F, true);
+ *
+ * Then you can use the following for the RTC_Table:
+ *
+ *   MCP7940M_RTC_TBL_ENTRY("/dev/rtc", &rtc_ctx)
+ */
+
+struct mcp7940m_rtc {
+  /** Just initialize with RTEMS_MUTEX_INITIALIZER('mcp7940'). */
+  rtems_mutex mutex;
+
+  /** The path of the I2C bus device. */
+  const char *i2c_bus_path;
+
+  /** I2C address. */
+  uint8_t i2c_addr;
+
+  /** True if a crystal should be used. False if an oscillator is connected. */
+  bool crystal;
+
+  /** Whether the RTC has already been initialized. Used internally. */
+  bool initialized;
+};
+
+#define MCP7940M_RTC_INITIALIZER(i2c_path, i2c_address, has_crystal) { \
+    .mutex = RTEMS_MUTEX_INITIALIZER("mcp7940m"), \
+    .i2c_bus_path = i2c_path, \
+    .i2c_addr = i2c_address, \
+    .crystal = has_crystal, \
+    .initialized = false, \
+  }
+
+#define MCP7940M_RTC_TBL_ENTRY(dev_name, mcp7940m_rtc_ctx) \
+  { \
+    .sDeviceName = dev_name, \
+    .deviceType = RTC_CUSTOM, \
+    .pDeviceFns = &rtc_mcp7940m_fns, \
+    .deviceProbe = rtc_mcp7940m_probe, \
+    .pDeviceParams = (void *)mcp7940m_rtc_ctx, \
+    .ulCtrlPort1 = 0, \
+    .ulDataPort = 0, \
+    .getRegister = NULL, \
+    .setRegister = NULL, \
+  }
+
+#ifdef __cplusplus
+}
+#endif /* __cplusplus */
+
+#endif /* LIBCHIP_MCP7940M_RTC_H */

spec/build/bsps/obj.yml

@@ -42,6 +42,7 @@ install:
   - bsps/include/libchip/ide_ctrl_cfg.h
   - bsps/include/libchip/ide_ctrl_io.h
   - bsps/include/libchip/m48t08.h
+  - bsps/include/libchip/mcp7940m-rtc.h
   - bsps/include/libchip/ns16550.h
   - bsps/include/libchip/ns16550_p.h
   - bsps/include/libchip/rtc.h
@@ -93,6 +94,7 @@ source:
 - bsps/shared/dev/rtc/m48t08_reg2.c
 - bsps/shared/dev/rtc/m48t08_reg4.c
 - bsps/shared/dev/rtc/m48t08_reg8.c
+- bsps/shared/dev/rtc/mcp7940m.c
 - bsps/shared/dev/rtc/rtcprobe.c
 - bsps/shared/dev/serial/arm-pl011.c
 - bsps/shared/dev/serial/ns16550-context.c