From 759598f82f02cc84614450807cb5de43ca18a339 Mon Sep 17 00:00:00 2001 From: Graeme Russ Date: Sat, 24 Apr 2010 00:05:41 +1000 Subject: x86: Split sc520 memory sizing versus reporting This patch allows the low-level assembler boot-strap to obtain the RAM size without calling the destructive 'sizer' routine. This allows boot-strapping from a U-Boot image loaded in RAM Signed-off-by: Graeme Russ --- arch/i386/cpu/start.S | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'arch/i386/cpu/start.S') diff --git a/arch/i386/cpu/start.S b/arch/i386/cpu/start.S index 25d32e6..1980f1a 100644 --- a/arch/i386/cpu/start.S +++ b/arch/i386/cpu/start.S @@ -63,6 +63,11 @@ early_board_init_ret: jmp mem_init mem_init_ret: + /* fetch memory size (into %eax) */ + mov $get_mem_size_ret, %ebp + jmp get_mem_size +get_mem_size_ret: + /* Check we have enough memory for stack */ movl $CONFIG_SYS_STACK_SIZE, %ecx cmpl %ecx, %eax -- cgit v1.1 From 077e1958ca4afe12d88043b123ded058c51b89f7 Mon Sep 17 00:00:00 2001 From: Graeme Russ Date: Sat, 24 Apr 2010 00:05:42 +1000 Subject: x86: Add RAM bootstrap functionality Add a parameter to the 32-bit entry to indicate if entry is from Real Mode or not. If entry is from Real Mode, execute the destructive 'sizer' routine to determine memory size as we are booting cold and running in Flash. If not entering from Real Mode, we are executing a U-Boot image from RAM and therefore the memory size is already known (and running 'sizer' will destroy the running image) There are now two 32-bit entry points. The first is the 'in RAM' entry point which exists at the start of the U-Boot binary image. As such, you can load u-boot.bin in RAM and jump directly to the load address without needing to calculate any offsets. The second entry point is used by the real-to-protected mode switch This patch also changes TEXT_BASE to 0x6000000 (in RAM). You can load the resulting image at 0x6000000 and simple go 0x6000000 from the u-boot prompt Hopefully a later patch will completely elliminate any dependency on TEXT_BASE like a relocatable linux kernel (perfect world) Signed-off-by: Graeme Russ --- arch/i386/cpu/start.S | 36 ++++++++++++++++++++++++++++++++++++ 1 file changed, 36 insertions(+) (limited to 'arch/i386/cpu/start.S') diff --git a/arch/i386/cpu/start.S b/arch/i386/cpu/start.S index 1980f1a..3cea04b 100644 --- a/arch/i386/cpu/start.S +++ b/arch/i386/cpu/start.S @@ -33,7 +33,27 @@ .type _start, @function .globl _i386boot_start _i386boot_start: + /* + * This is the fail safe 32-bit bootstrap entry point. The + * following code is not executed from a cold-reset (actually, a + * lot of it is, but from real-mode after cold reset. It is + * repeated here to put the board into a state as close to cold + * reset as necessary) + */ + cli + cld + + /* Turn of cache (this might require a 486-class CPU) */ + movl %cr0, %eax + orl $0x60000000,%eax + movl %eax, %cr0 + wbinvd + + /* Tell 32-bit code it is being entered from an in-RAM copy */ + movw $0x0000, %bx _start: + /* This is the 32-bit cold-reset entry point */ + movl $0x18,%eax /* Load our segement registes, the * gdt have already been loaded by start16.S */ movw %ax,%fs @@ -42,6 +62,18 @@ _start: movw %ax,%es movw %ax,%ss + /* Clear the interupt vectors */ + lidt blank_idt_ptr + + /* + * Skip low-level board and memory initialization if not starting + * from cold-reset. This allows us to do a fail safe boot-strap + * into a new build of U-Boot from a known-good boot flash + */ + movw $0x0001, %ax + cmpw %ax, %bx + jne mem_init_ret + /* We call a few functions in the board support package * since we have no stack yet we'll have to use %ebp * to store the return address */ @@ -138,3 +170,7 @@ stack_ok: die: hlt jmp die hlt + +blank_idt_ptr: + .word 0 /* limit */ + .long 0 /* base */ -- cgit v1.1 From c14a3669b22d3e430b416cdee92b751f13697a1f Mon Sep 17 00:00:00 2001 From: Graeme Russ Date: Sat, 24 Apr 2010 00:05:43 +1000 Subject: x86: Move GDT to a safe location in RAM Currently, the GDT is either located in FLASH or in the non-relocated U-Boot image in RAM. Both of these locations are unsafe as those locations can be erased during a U-Boot update. Move the GDT into the highest available memory location and relocate U-Boot to just below it Signed-off-by: Graeme Russ --- arch/i386/cpu/start.S | 96 +++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 96 insertions(+) (limited to 'arch/i386/cpu/start.S') diff --git a/arch/i386/cpu/start.S b/arch/i386/cpu/start.S index 3cea04b..7def8de 100644 --- a/arch/i386/cpu/start.S +++ b/arch/i386/cpu/start.S @@ -100,6 +100,53 @@ mem_init_ret: jmp get_mem_size get_mem_size_ret: + /* + * We are now in 'Flat Protected Mode' and we know how much memory + * the board has. The (temporary) Global Descriptor Table is not + * in a 'Safe' place (it is either in Flash which can be erased or + * reprogrammed or in a fail-safe boot-strap image which could be + * over-written). + * + * Move the final gdt to a safe place (top of RAM) and load it. + * This is not a trivial excercise - the lgdt instruction does not + * have a register operand (memory only) and we may well be + * running from Flash, so self modifying code will not work here. + * To overcome this, we copy a stub into upper memory along with + * the GDT. + */ + + /* Reduce upper memory limit by (Stub + GDT Pointer + GDT) */ + subl $(end_gdt_setup - start_gdt_setup), %eax + + /* Copy the GDT and Stub */ + movl $start_gdt_setup, %esi + movl %eax, %edi + movl $(end_gdt_setup - start_gdt_setup), %ecx + shrl $2, %ecx + cld + rep movsl + + /* write the lgdt 'parameter' */ + subl $(jmp_instr - start_gdt_setup - 4), %ebp + addl %eax, %ebp + movl $(gdt_ptr - start_gdt_setup), %ebx + addl %eax, %ebx + movl %ebx, (%ebp) + + /* write the gdt address into the pointer */ + movl $(gdt_addr - start_gdt_setup), %ebp + addl %eax, %ebp + movl $(gdt - start_gdt_setup), %ebx + addl %eax, %ebx + movl %ebx, (%ebp) + + /* Save the return address */ + movl $load_gdt_ret, %ebp + + /* Load the new (safe) Global Descriptor Table */ + jmp *%eax + +load_gdt_ret: /* Check we have enough memory for stack */ movl $CONFIG_SYS_STACK_SIZE, %ecx cmpl %ecx, %eax @@ -174,3 +221,52 @@ die: hlt blank_idt_ptr: .word 0 /* limit */ .long 0 /* base */ + +.align 4 +start_gdt_setup: + lgdt gdt_ptr +jmp_instr: + jmp *%ebp + +.align 4 +gdt_ptr: + .word 0x30 /* limit (48 bytes = 6 GDT entries) */ +gdt_addr: + .long gdt /* base */ + + /* The GDT table ... + * + * Selector Type + * 0x00 NULL + * 0x08 Unused + * 0x10 32bit code + * 0x18 32bit data/stack + * 0x20 16bit code + * 0x28 16bit data/stack + */ + +.align 4 +gdt: + .word 0, 0, 0, 0 /* NULL */ + .word 0, 0, 0, 0 /* unused */ + + .word 0xFFFF /* 4Gb - (0x100000*0x1000 = 4Gb) */ + .word 0 /* base address = 0 */ + .word 0x9B00 /* code read/exec */ + .word 0x00CF /* granularity = 4096, 386 (+5th nibble of limit) */ + + .word 0xFFFF /* 4Gb - (0x100000*0x1000 = 4Gb) */ + .word 0x0 /* base address = 0 */ + .word 0x9300 /* data read/write */ + .word 0x00CF /* granularity = 4096, 386 (+5th nibble of limit) */ + + .word 0xFFFF /* 64kb */ + .word 0 /* base address = 0 */ + .word 0x9b00 /* data read/write */ + .word 0x0010 /* granularity = 1 (+5th nibble of limit) */ + + .word 0xFFFF /* 64kb */ + .word 0 /* base address = 0 */ + .word 0x9300 /* data read/write */ + .word 0x0010 /* granularity = 1 (+5th nibble of limit) */ +end_gdt_setup: -- cgit v1.1