pl031: Add pl031 rtc support

Add support for the pl031, a popular RTC chip used by many devices,
including qemu-virt.

Signed-off-by: Pedro Falcato <pedro.falcato@gmail.com>

kernel/configs/kernel.config.arm64

@@ -25,3 +25,4 @@ CONFIG_RTL8168=y
 CONFIG_RISCV=n
 CONFIG_ARM64=y
 CONFIG_SERIAL_PL011=y
+CONFIG_PL031_RTC=y

kernel/drivers/rtc/Makefile

@@ -1,2 +1,3 @@
 obj-$(CONFIG_X86)+= drivers/rtc/rtc.o
 obj-$(CONFIG_GOLDFISH_RTC)+= drivers/rtc/goldfish-rtc.o
+obj-$(CONFIG_PL031_RTC)+= drivers/rtc/pl031-rtc.o

kernel/drivers/rtc/pl031-rtc.cpp

@@ -0,0 +1,114 @@
+/*
+ * Copyright (c) 2023 Pedro Falcato
+ * This file is part of Onyx, and is released under the terms of the MIT License
+ * check LICENSE at the root directory for more information
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+#include <onyx/clock.h>
+#include <onyx/dev.h>
+#include <onyx/device_tree.h>
+#include <onyx/types.h>
+
+#include <onyx/hwregister.hpp>
+
+#define RTC_DR 0x0
+#define RTC_LR 0x8
+#define RTC_CR 0x0c
+
+class pl031_dev
+{
+private:
+    dev_resource *rsrc_;
+    unsigned int irq_;
+    hw_range range_;
+
+public:
+    pl031_dev(dev_resource *io, unsigned int irq) : rsrc_{io}, irq_{irq}, range_{rsrc_}
+    {
+    }
+
+    int init();
+
+    u64 get_time()
+    {
+        return range_.read32(RTC_DR);
+    }
+
+    int set_time(u64 time_epoch)
+    {
+        if (time_epoch > UINT32_MAX)
+        {
+            printf("pl031: The device does not support 64-bit time (tried to set time=%lx)\n",
+                   time_epoch);
+            return -EIO;
+        }
+
+        range_.write32(RTC_LR, (u32) time_epoch);
+        return 0;
+    }
+};
+
+#define RTC_CR_START (1 << 0)
+
+int pl031_dev::init()
+{
+    if (!range_.init(rsrc_))
+        return -ENOMEM;
+    printf("pl031: initializing...\n");
+
+    if (!(range_.read32(RTC_CR) & RTC_CR_START))
+    {
+        // We must only write the RTC start bit
+        // *IF* it is not started already, else we reset the clock.
+        range_.write32(RTC_CR, RTC_CR_START);
+    }
+
+    struct clock_time clk;
+    clk.epoch = get_time();
+    clk.measurement_timestamp = clocksource_get_time();
+    time_set(CLOCK_REALTIME, &clk);
+    return 0;
+}
+
+int pl031_dt_probe(device *fake_dev)
+{
+    auto dev = (device_tree::node *) fake_dev;
+
+    // Find IRQ, IO resources
+    auto irq_rc = dev->get_resource(DEV_RESOURCE_FLAG_IRQ);
+    if (!irq_rc)
+        return -1;
+
+    auto iorsrc = dev->get_resource(DEV_RESOURCE_FLAG_MEM | DEV_RESOURCE_FLAG_IO_PORT);
+    if (!iorsrc)
+        return -1;
+
+    unique_ptr<pl031_dev> gdev =
+        make_unique<pl031_dev>(iorsrc, static_cast<uint16_t>(irq_rc->start()));
+    if (!gdev)
+        return -ENOMEM;
+
+    if (int st = gdev->init(); st < 0)
+        return st;
+    gdev.release();
+    return 0;
+}
+
+static const char *pl031_compatible_ids[] = {"arm,pl031", nullptr};
+
+static driver pl031_driver = {
+    .name = "pl031",
+    .devids = pl031_compatible_ids,
+    .probe = pl031_dt_probe,
+    .bus_type_node = &pl031_driver,
+};
+
+int pl031_dt_init()
+{
+    device_tree::register_driver(&pl031_driver);
+    return 0;
+}
+
+DRIVER_INIT(pl031_dt_init);