[U-Boot] [RFC][PATCH 25/36] x86 - Use Cache-As-RAM for initial stack

Graeme Russ graeme.russ at gmail.com
Mon Jan 3 20:46:45 CET 2011 

---
 arch/i386/cpu/sc520/Makefile    |    1 +
 arch/i386/cpu/sc520/sc520_asm.S |    6 +-
 arch/i386/cpu/sc520/sc520_car.S |   94 +++++++++++++++++++++++++++++++++++++++
 arch/i386/cpu/start.S           |   35 +++++++-------
 include/configs/eNET.h          |   18 +++++++
 5 files changed, 133 insertions(+), 21 deletions(-)
 create mode 100644 arch/i386/cpu/sc520/sc520_car.S

diff --git a/arch/i386/cpu/sc520/Makefile b/arch/i386/cpu/sc520/Makefile
index b962b02..3c25cba 100644
--- a/arch/i386/cpu/sc520/Makefile
+++ b/arch/i386/cpu/sc520/Makefile
@@ -37,6 +37,7 @@ COBJS-$(CONFIG_SYS_SC520_SSI) += sc520_ssi.o
 COBJS-$(CONFIG_SYS_SC520_TIMER) += sc520_timer.o

 SOBJS-$(CONFIG_SYS_SC520) += sc520_asm.o
+SOBJS-$(CONFIG_SYS_SC520) += sc520_car.o

 SRCS	:= $(SOBJS-y:.o=.S) $(COBJS-y:.o=.c)
 OBJS	:= $(addprefix $(obj),$(SOBJS-y) $(COBJS-y))
diff --git a/arch/i386/cpu/sc520/sc520_asm.S b/arch/i386/cpu/sc520/sc520_asm.S
index f2bc47b..2e85370 100644
--- a/arch/i386/cpu/sc520/sc520_asm.S
+++ b/arch/i386/cpu/sc520/sc520_asm.S
@@ -515,7 +515,7 @@ bad_ram:
 dram_done:
 	/* Restore Boot Flags */
 	movl	%ebx, %ebp
-	jmp	mem_init_ret
+	ret

 #if CONFIG_SYS_SDRAM_ECC_ENABLE
 .globl init_ecc
@@ -560,7 +560,7 @@ set_ecc:
 	movb	%al,(%edi)

 out:
-	jmp	init_ecc_ret
+	ret
 #endif

 /*
@@ -605,4 +605,4 @@ bank3:	movl	(%edi), %eax

 done:
 	movl	%edx, %eax
-	jmp	get_mem_size_ret
+	ret
diff --git a/arch/i386/cpu/sc520/sc520_car.S b/arch/i386/cpu/sc520/sc520_car.S
new file mode 100644
index 0000000..22f5225
--- /dev/null
+++ b/arch/i386/cpu/sc520/sc520_car.S
@@ -0,0 +1,94 @@
+/*
+ * (C) Copyright 2010
+ * Graeme Russ <graeme.russ at gmail.com>.
+ *
+ * See file CREDITS for list of people who contributed to this
+ * project.
+ *
+ * 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; either version 2 of
+ * the License, or (at your option) any later version.
+ *
+ * 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.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston,
+ * MA 02111-1307 USA
+ */
+
+
+#include <config.h>
+#include <asm/processor-flags.h>
+#include <asm/ic/sc520.h>
+
+.section .text
+
+.globl car_init
+car_init:
+	/*
+	 * How to enable Cache-As-RAM for the AMD Elan SC520:
+	 *  1. Turn off the CPU Cache (may not be strictly required)
+	 *  2. Set code execution PAR (usually the BOOTCS region) to be
+	 *     non-cachable
+	 *  3. Create a Cachable PAR Region for an area of memory which is
+	 *       a) NOT where the code is being executed
+	 *       b) NOT SDRAM (Controller not initialised yet)
+	 *       c) WILL response to read requests
+	 *     The easiest way to do this is to create a second BOOTCS
+	 *     PAR mappnig with an address != the PAR in step 2
+	 *  4. Issue a wbinvd to invalidate the CPU cache
+	 *  5. Turn on the CPU Cache
+	 *  6. Read 16kB from the cached PAR region setup in step 3
+	 *  7. Turn off the CPU Cache (but DO NOT issue a wbinvd)
+	 *
+	 * The following code uses PAR2 as the cached PAR (PAR0 and PAR1
+	 * are avoided as these are the only two PARs which can be used
+	 * as PCI BUS Memory regions which the board might require)
+	 *
+	 * The configuration of PAR2 must be set in the board configuration
+	 * file as CONFIG_SYS_SC520_CAR_PAR
+	 */
+
+	/* Configure Cache-As-RAM PAR */
+	movl	$CONFIG_SYS_SC520_CAR_PAR, %eax
+	movl	$SC520_PAR2, %edi
+	movl	%eax, (%edi)
+
+	/* Trash the cache then turn it on */
+	wbinvd
+	movl	%cr0, %eax
+	andl	$~(X86_CR0_NW | X86_CR0_CD), %eax
+	movl	%eax, %cr0
+
+	/*
+	 * The cache is now enabled and empty. Map a region of memory to
+	 * it by reading that region.
+	 */
+	movl	$CONFIG_SYS_CAR_ADDR, %esi
+	movl	$CONFIG_SYS_CAR_SIZE, %ecx
+	shrl	$2, %ecx			/* we are reading longs */
+	cld
+	rep	lodsl
+
+	/* Turn off the cache, but don't trash it */
+	movl	%cr0, %eax
+	orl	$(X86_CR0_NW | X86_CR0_CD), %eax
+	movl	%eax, %cr0
+
+	/* Clear the CAR region */
+	xorl	%eax, %eax
+	movl	$CONFIG_SYS_CAR_ADDR, %edi
+	movl	$CONFIG_SYS_CAR_SIZE, %ecx
+	shrl	$2, %ecx			/* we are writing longs */
+	rep	stosl
+
+	/*
+	 * Done - We should now have CONFIG_SYS_CAR_SIZE bytes of
+	 * Cache-As-RAM
+	 */
+	jmp	car_init_ret
diff --git a/arch/i386/cpu/start.S b/arch/i386/cpu/start.S
index 0ce9713..df9ca0d 100644
--- a/arch/i386/cpu/start.S
+++ b/arch/i386/cpu/start.S
@@ -72,41 +72,40 @@ _start:
 .globl early_board_init_ret
 early_board_init_ret:

+	/* Initialise Cache-As-RAM */
+	jmp	car_init
+.globl car_init_ret
+car_init_ret:
+	/*
+	 * We now have CONFIG_SYS_CAR_SIZE bytes of Cache-As-RAM (or SRAM,
+	 * or fully initialised SDRAM - we really don't care which)
+	 * starting at CONFIG_SYS_CAR_ADDR to be used as a temporary stack
+	 */
+	movl	$CONFIG_SYS_INIT_SP_ADDR, %esp
+
 	/* Skip memory initialization if not starting from cold-reset */
 	movl	%ebx, %ecx
 	andl	$GD_FLG_COLD_BOOT, %ecx
 	jz	skip_mem_init

 	/* size memory */
-	jmp	mem_init
-.globl mem_init_ret
-mem_init_ret:
+	call	mem_init

 skip_mem_init:
 	/* fetch memory size (into %eax) */
-	jmp	get_mem_size
-.globl get_mem_size_ret
-get_mem_size_ret:
+	call	get_mem_size
+	movl	%eax, %esp

 #if CONFIG_SYS_SDRAM_ECC_ENABLE
 	/* Skip ECC initialization if not starting from cold-reset */
 	movl	%ebx, %ecx
 	andl	$GD_FLG_COLD_BOOT, %ecx
-	jz	init_ecc_ret
-	jmp	init_ecc
+	jz	skip_ecc_init
+	call	init_ecc

-.globl init_ecc_ret
-init_ecc_ret:
+skip_init_ecc:
 #endif

-	/* Check we have enough memory for stack */
-	movl	$CONFIG_SYS_STACK_SIZE, %ecx
-	cmpl	%ecx, %eax
-	jb	die
-mem_ok:
-	/* Set stack pointer to upper memory limit*/
-	movl	%eax, %esp
-
 	/* Test the stack */
 	pushl	$0
 	popl	%ecx
diff --git a/include/configs/eNET.h b/include/configs/eNET.h
index 59f8e6d..4b9d649 100644
--- a/include/configs/eNET.h
+++ b/include/configs/eNET.h
@@ -172,6 +172,9 @@
  * Memory organization
  */
 #define CONFIG_SYS_STACK_SIZE		0x8000  	/* Size of bootloader stack */
+#define CONFIG_SYS_CAR_ADDR		0x19200000
+#define CONFIG_SYS_CAR_SIZE		0x00004000
+#define CONFIG_SYS_INIT_SP_ADDR		(CONFIG_SYS_CAR_ADDR + CONFIG_SYS_CAR_SIZE)
 #define CONFIG_SYS_BL_START_FLASH	0x38040000	/* Address of relocated code */
 #define CONFIG_SYS_BL_START_RAM		0x03fd0000	/* Address of relocated code */
 #define CONFIG_SYS_MONITOR_BASE		CONFIG_SYS_TEXT_BASE
@@ -289,6 +292,21 @@
  */

 /*
+ * Cache-As-RAM (Targets Boot Flash)
+ *
+ * 100 1 0 0 0 0001111 011001001000000000 }- 0x903d9200
+ * \ / | | | | \--+--/ \-------+--------/
+ *  |  | | | |    |            +------------ Start at 0x19200000
+ *  |  | | | |    +------------------------- 64k Region Size ((15 + 1) * 4kB)
+ *  |  | | | +------------------------------ 4kB Page Size
+ *  |  | | +-------------------------------- Writes Enabled
+ *  |  | +---------------------------------- Caching Enabled
+ *  |  +------------------------------------ Execution Prevented
+ *  +--------------------------------------- BOOTCS
+ */
+#define CONFIG_SYS_SC520_CAR_PAR		0x903d9200
+
+/*
  * PAR for Boot Flash (BOOTCS, 512kB @ 0x38000000)
  *
  * 100 0 1 0 1 00000000111 11100000000000 }- 0x8a01f800
--
1.7.1.422.g049e9

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