MIPS: Support dynamic I/O port base address

The existing mips_io_port_base variable isn't suitable for use early
during boot since it will be stored in the .data section which may not
be writable pre-relocation. Fix this by moving the I/O port base address
into struct arch_global_data. In order to avoid adding this field for
all targets, make this dependant upon a new Kconfig entry
CONFIG_DYNAMIC_IO_PORT_BASE. Malta is the only board which sets a
non-zero I/O port base, so select this option only for Malta.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>

arch/mips/Kconfig

@@ -23,6 +23,7 @@ config TARGET_QEMU_MIPS
 
 config TARGET_MALTA
 	bool "Support malta"
+	select DYNAMIC_IO_PORT_BASE
 	select SUPPORTS_BIG_ENDIAN
 	select SUPPORTS_LITTLE_ENDIAN
 	select SUPPORTS_CPU_MIPS32_R1
@@ -217,6 +218,9 @@ config MIPS_L1_CACHE_SHIFT
 	default "4" if MIPS_L1_CACHE_SHIFT_4
 	default "5"
 
+config DYNAMIC_IO_PORT_BASE
+	bool
+
 endif
 
 endmenu

arch/mips/include/asm/global_data.h

@@ -12,6 +12,9 @@
 
 /* Architecture-specific global data */
 struct arch_global_data {
+#ifdef CONFIG_DYNAMIC_IO_PORT_BASE
+	unsigned long io_port_base;
+#endif
 #ifdef CONFIG_JZSOC
 	/* There are other clocks in the jz4740 */
 	unsigned long per_clk;	/* Peripheral bus clock */

arch/mips/include/asm/io.h

@@ -41,31 +41,37 @@
 
 #define IO_SPACE_LIMIT 0xffff
 
-/*
- * On MIPS I/O ports are memory mapped, so we access them using normal
- * load/store instructions. mips_io_port_base is the virtual address to
- * which all ports are being mapped.  For sake of efficiency some code
- * assumes that this is an address that can be loaded with a single lui
- * instruction, so the lower 16 bits must be zero.  Should be true on
- * on any sane architecture; generic code does not use this assumption.
- */
-extern const unsigned long mips_io_port_base;
+#ifdef CONFIG_DYNAMIC_IO_PORT_BASE
+
+static inline ulong mips_io_port_base(void)
+{
+	DECLARE_GLOBAL_DATA_PTR;
+
+	return gd->arch.io_port_base;
+}
 
-/*
- * Gcc will generate code to load the value of mips_io_port_base after each
- * function call which may be fairly wasteful in some cases.  So we don't
- * play quite by the book.  We tell gcc mips_io_port_base is a long variable
- * which solves the code generation issue.  Now we need to violate the
- * aliasing rules a little to make initialization possible and finally we
- * will need the barrier() to fight side effects of the aliasing chat.
- * This trickery will eventually collapse under gcc's optimizer.  Oh well.
- */
 static inline void set_io_port_base(unsigned long base)
 {
-	* (unsigned long *) &mips_io_port_base = base;
+	DECLARE_GLOBAL_DATA_PTR;
+
+	gd->arch.io_port_base = base;
 	barrier();
 }
 
+#else /* !CONFIG_DYNAMIC_IO_PORT_BASE */
+
+static inline ulong mips_io_port_base(void)
+{
+	return 0;
+}
+
+static inline void set_io_port_base(unsigned long base)
+{
+	BUG_ON(base);
+}
+
+#endif /* !CONFIG_DYNAMIC_IO_PORT_BASE */
+
 /*
  *     virt_to_phys    -       map virtual addresses to physical
  *     @address: address to remap
@@ -293,7 +299,7 @@ static inline void pfx##out##bwlq##p(type val, unsigned long port)	\
 									\
 	war_octeon_io_reorder_wmb();					\
 									\
-	__addr = (void *)__swizzle_addr_##bwlq(mips_io_port_base + port); \
+	__addr = (void *)__swizzle_addr_##bwlq(mips_io_port_base() + port); \
 									\
 	__val = pfx##ioswab##bwlq(__addr, val);				\
 									\
@@ -308,7 +314,7 @@ static inline type pfx##in##bwlq##p(unsigned long port)			\
 	volatile type *__addr;						\
 	type __val;							\
 									\
-	__addr = (void *)__swizzle_addr_##bwlq(mips_io_port_base + port); \
+	__addr = (void *)__swizzle_addr_##bwlq(mips_io_port_base() + port); \
 									\
 	BUILD_BUG_ON(sizeof(type) > sizeof(unsigned long));		\
 									\

arch/mips/lib/Makefile

@@ -7,7 +7,6 @@
 
 obj-y	+= cache.o
 obj-y	+= cache_init.o
-obj-y	+= io.o
 
 obj-$(CONFIG_CMD_BOOTM) += bootm.o
 

arch/mips/lib/io.c

@@ -1,12 +0,0 @@
-/*
- * (C) Copyright 2003
- * Wolfgang Denk, DENX Software Engineering, wd@denx.de.
- *
- * SPDX-License-Identifier:	GPL-2.0+
- */
-
-/*
- * mips_io_port_base is the begin of the address space to which x86 style
- * I/O ports are mapped.
- */
-const unsigned long mips_io_port_base = -1;