lx_emul: support CLK_OF_DECLARE initcall mechanism

Clock providers such as drivers/clk/sunxi-ng/ccu-sun8i-r.c don't use
regular init calls but declare their init functions via CLK_OF_DECLARE,
which fill the __clk_of_table. Linux populates the table statically by
using special sections declared in the linker script. In contrast, we
populate the table by expanding the macro to global constructor
functions.

The __clk_of_table is then processed by the call of of_clk_init(NULL).

Issue #4253

repos/dde_linux/src/include/lx_emul/init.h

@@ -28,6 +28,8 @@ int  lx_emul_init_task_function(void * dtb);
 
 extern void * lx_emul_init_task_struct;
 
+void lx_emul_register_of_clk_initcall(char const *compat, void *fn);
+
 #ifdef __cplusplus
 }
 #endif

repos/dde_linux/src/include/lx_emul/shadow/linux/of.h

@@ -0,0 +1,27 @@
+/*
+ * \brief  Shadow copy of linux/of.h
+ * \author Norman Feske
+ * \date   2021-08-19
+ */
+
+/*
+ * Copyright (C) 2021 Genode Labs GmbH
+ *
+ * This file is distributed under the terms of the GNU General Public License
+ * version 2.
+ */
+
+#ifndef _LX_EMUL__SHADOW__LINUX__OF_H_
+#define _LX_EMUL__SHADOW__LINUX__OF_H_
+
+#include_next <linux/of.h>
+#include      <lx_emul/init.h>
+
+#undef OF_DECLARE_1
+
+#define OF_DECLARE_1(table, name, compat, fn) \
+	static void __of_declare_initcall_##fn##name(void)__attribute__((constructor)); \
+	static void __of_declare_initcall_##fn##name() { \
+			lx_emul_register_of_##table##_initcall(compat, fn); };
+
+#endif /* _LX_EMUL__SHADOW__LINUX__OF_H_ */

repos/dde_linux/src/lib/lx_emul/clocksource.c

@@ -15,8 +15,10 @@
 #include <linux/clocksource.h>
 #include <linux/sched_clock.h>
 #include <linux/smp.h>
+#include <linux/of_clk.h>
 #include <lx_emul/debug.h>
 #include <lx_emul/time.h>
+#include <lx_emul/init.h>
 
 static u32 dde_timer_rate = 1000000; /* we use microseconds as rate */
 
@@ -93,6 +95,10 @@ void lx_emul_time_init()
 	timecounter_init(&timecounter, &cyclecounter, start_count);
 	clockevents_config_and_register(&clock_event_device, dde_timer_rate, 0xf, 0x7fffffff);
 	sched_clock_register(dde_timer_read_counter, 64, dde_timer_rate);
+
+	/* execute setup calls of clock providers in __clk_of_table */
+	of_clk_init(NULL);
+
 }
 
 
@@ -102,4 +108,25 @@ void lx_emul_time_handle(void)
 }
 
 
-struct of_device_id __clk_of_table[] = { };
+enum { LX_EMUL_MAX_OF_CLOCK_PROVIDERS = 256 };
+
+
+struct of_device_id __clk_of_table[LX_EMUL_MAX_OF_CLOCK_PROVIDERS] = { };
+
+
+void lx_emul_register_of_clk_initcall(char const *compat, void *fn)
+{
+	static unsigned count;
+
+	if (count == LX_EMUL_MAX_OF_CLOCK_PROVIDERS) {
+		printk("lx_emul_register_of_clk_initcall: __clk_of_table exhausted\n");
+		return;
+	}
+
+	strncpy(__clk_of_table[count].compatible, compat,
+	        sizeof(__clk_of_table[count].compatible));
+
+	__clk_of_table[count].data = fn;
+
+	count++;
+}

repos/dde_linux/src/lib/lx_emul/shadow/drivers/clk/clk.c

@@ -45,3 +45,10 @@ void clk_disable(struct clk * clk) { }
 
 
 void clk_unprepare(struct clk * clk) { }
+
+
+struct of_device_id;
+
+
+void of_clk_init(const struct of_device_id *matches) { }
+