RISC-V: Task implementation

This patch contains the implementation of tasks on RISC-V, most of which
is involved in task switching.

Signed-off-by: Palmer Dabbelt <palmer@dabbelt.com>

arch/riscv/include/asm/thread_info.h

@@ -0,0 +1,94 @@
+/*
+ * Copyright (C) 2009 Chen Liqin <liqin.chen@sunplusct.com>
+ * Copyright (C) 2012 Regents of the University of California
+ * Copyright (C) 2017 SiFive
+ *
+ *   This program is free software; you can redistribute it and/or
+ *   modify it under the terms of the GNU General Public License
+ *   as published by the Free Software Foundation, version 2.
+ *
+ *   This program is distributed in the hope that it will be useful,
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *   GNU General Public License for more details.
+ */
+
+#ifndef _ASM_RISCV_THREAD_INFO_H
+#define _ASM_RISCV_THREAD_INFO_H
+
+#include <asm/page.h>
+#include <linux/const.h>
+
+/* thread information allocation */
+#define THREAD_SIZE_ORDER	(1)
+#define THREAD_SIZE		(PAGE_SIZE << THREAD_SIZE_ORDER)
+
+#ifndef __ASSEMBLY__
+
+#include <asm/processor.h>
+#include <asm/csr.h>
+
+typedef unsigned long mm_segment_t;
+
+/*
+ * low level task data that entry.S needs immediate access to
+ * - this struct should fit entirely inside of one cache line
+ * - if the members of this struct changes, the assembly constants
+ *   in asm-offsets.c must be updated accordingly
+ * - thread_info is included in task_struct at an offset of 0.  This means that
+ *   tp points to both thread_info and task_struct.
+ */
+struct thread_info {
+	unsigned long		flags;		/* low level flags */
+	int                     preempt_count;  /* 0=>preemptible, <0=>BUG */
+	mm_segment_t		addr_limit;
+	/*
+	 * These stack pointers are overwritten on every system call or
+	 * exception.  SP is also saved to the stack it can be recovered when
+	 * overwritten.
+	 */
+	long			kernel_sp;	/* Kernel stack pointer */
+	long			user_sp;	/* User stack pointer */
+	int			cpu;
+};
+
+/*
+ * macros/functions for gaining access to the thread information structure
+ *
+ * preempt_count needs to be 1 initially, until the scheduler is functional.
+ */
+#define INIT_THREAD_INFO(tsk)			\
+{						\
+	.flags		= 0,			\
+	.preempt_count	= INIT_PREEMPT_COUNT,	\
+	.addr_limit	= KERNEL_DS,		\
+}
+
+#define init_stack		(init_thread_union.stack)
+
+#endif /* !__ASSEMBLY__ */
+
+/*
+ * thread information flags
+ * - these are process state flags that various assembly files may need to
+ *   access
+ * - pending work-to-be-done flags are in lowest half-word
+ * - other flags in upper half-word(s)
+ */
+#define TIF_SYSCALL_TRACE	0	/* syscall trace active */
+#define TIF_NOTIFY_RESUME	1	/* callback before returning to user */
+#define TIF_SIGPENDING		2	/* signal pending */
+#define TIF_NEED_RESCHED	3	/* rescheduling necessary */
+#define TIF_RESTORE_SIGMASK	4	/* restore signal mask in do_signal() */
+#define TIF_MEMDIE		5	/* is terminating due to OOM killer */
+#define TIF_SYSCALL_TRACEPOINT  6       /* syscall tracepoint instrumentation */
+
+#define _TIF_SYSCALL_TRACE	(1 << TIF_SYSCALL_TRACE)
+#define _TIF_NOTIFY_RESUME	(1 << TIF_NOTIFY_RESUME)
+#define _TIF_SIGPENDING		(1 << TIF_SIGPENDING)
+#define _TIF_NEED_RESCHED	(1 << TIF_NEED_RESCHED)
+
+#define _TIF_WORK_MASK \
+	(_TIF_NOTIFY_RESUME | _TIF_SIGPENDING | _TIF_NEED_RESCHED)
+
+#endif /* _ASM_RISCV_THREAD_INFO_H */