[U-Boot] [PATCH 5/8] xtensa: add support for the xtensa processor architecture [1/2]
Max Filippov
jcmvbkbc at gmail.com
Wed Aug 20 19:42:10 CEST 2014
From: Chris Zankel <chris at zankel.net>
The Xtensa processor architecture is a configurable, extensible,
and synthesizable 32-bit RISC processor core provided by Cadence.
This is the first part of the basic architecture port with changes to
common files. The 'arch/xtensa' directory, and boards and additional
drivers will be in separate commits.
Signed-off-by: Chris Zankel <chris at zankel.net>
Signed-off-by: Max Filippov <jcmvbkbc at gmail.com>
---
CREDITS | 5 +++
MAKEALL | 6 +++
Makefile | 1 +
common/board_r.c | 2 +-
common/cmd_bdinfo.c | 22 ++++++++++
common/image.c | 1 +
doc/README.xtensa | 104 ++++++++++++++++++++++++++++++++++++++++++++
examples/standalone/stubs.c | 45 +++++++++++++++++++
include/image.h | 1 +
include/linux/stat.h | 4 +-
10 files changed, 188 insertions(+), 3 deletions(-)
create mode 100644 doc/README.xtensa
diff --git a/CREDITS b/CREDITS
index 3e5fb7b..55ad04c 100644
--- a/CREDITS
+++ b/CREDITS
@@ -534,3 +534,8 @@ N: Philip Balister
E: philip at opensdr.com
D: Port to Lyrtech SFFSDR development board.
W: www.opensdr.com
+
+N: Chris Zankel
+E: chris at zankel.net
+D: Port to Xtensa
+W: www.linux-xtensa.org
diff --git a/MAKEALL b/MAKEALL
index 929fe88..c22e5b7 100755
--- a/MAKEALL
+++ b/MAKEALL
@@ -505,6 +505,12 @@ LIST_nds32="$(targets_by_arch nds32)"
LIST_arc="$(targets_by_arch arc)"
+#########################################################################
+## Xtensa Systems
+#########################################################################
+
+LIST_xtensa="$(targets_by_arch xtensa)"
+
#-----------------------------------------------------------------------
get_target_location() {
diff --git a/Makefile b/Makefile
index 344492f..e6d8abf 100644
--- a/Makefile
+++ b/Makefile
@@ -656,6 +656,7 @@ endif
libs-$(CONFIG_ARM) += arch/arm/cpu/
libs-$(CONFIG_PPC) += arch/powerpc/cpu/
+libs-$(CONFIG_XTENSA) += arch/xtensa/cpu/
libs-y += $(if $(BOARDDIR),board/$(BOARDDIR)/)
diff --git a/common/board_r.c b/common/board_r.c
index 8e7a3ac..38c028a 100644
--- a/common/board_r.c
+++ b/common/board_r.c
@@ -911,7 +911,7 @@ void board_init_r(gd_t *new_gd, ulong dest_addr)
int i;
#endif
-#ifndef CONFIG_X86
+#if !defined(CONFIG_X86) && !defined(CONFIG_XTENSA)
gd = new_gd;
#endif
diff --git a/common/cmd_bdinfo.c b/common/cmd_bdinfo.c
index 3d37a86..fea4a55 100644
--- a/common/cmd_bdinfo.c
+++ b/common/cmd_bdinfo.c
@@ -536,6 +536,28 @@ int do_bdinfo(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
return 0;
}
+#elif defined(CONFIG_XTENSA)
+
+int do_bdinfo(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
+{
+ bd_t *bd = gd->bd;
+
+ print_num("boot_params", (ulong)bd->bi_boot_params);
+ print_num("memstart", (ulong)bd->bi_memstart);
+ print_lnum("memsize", (u64)bd->bi_memsize);
+ print_num("flashstart", (ulong)bd->bi_flashstart);
+ print_num("flashsize", (ulong)bd->bi_flashsize);
+ print_num("flashoffset", (ulong)bd->bi_flashoffset);
+
+#if defined(CONFIG_CMD_NET)
+ print_eth(0);
+ printf("ip_addr = %s\n", getenv("ipaddr"));
+#endif
+ printf("baudrate = %d bps\n", gd->baudrate);
+
+ return 0;
+}
+
#else
#error "a case for this architecture does not exist!"
#endif
diff --git a/common/image.c b/common/image.c
index 11b3cf5..159d004 100644
--- a/common/image.c
+++ b/common/image.c
@@ -85,6 +85,7 @@ static const table_entry_t uimage_arch[] = {
{ IH_ARCH_SANDBOX, "sandbox", "Sandbox", },
{ IH_ARCH_ARM64, "arm64", "AArch64", },
{ IH_ARCH_ARC, "arc", "ARC", },
+ { IH_ARCH_XTENSA, "xtensa", "Xtensa", },
{ -1, "", "", },
};
diff --git a/doc/README.xtensa b/doc/README.xtensa
new file mode 100644
index 0000000..980ab14
--- /dev/null
+++ b/doc/README.xtensa
@@ -0,0 +1,104 @@
+U-Boot for the Xtensa Architecture
+==================================
+
+Xtensa Architecture and Diamond Cores
+-------------------------------------
+
+Xtensa is a configurable processor architecture from Tensilica, Inc.
+Diamond Cores are pre-configured instances available for license and
+SoC cores in the same manner as ARM, MIPS, etc.
+
+Xtensa licensees create their own Xtensa cores with selected features
+and custom instructions, registers and co-processors. The custom core
+is configured with Tensilica tools and built with Tensilica's Xtensa
+Processor Generator.
+
+There are an effectively infinite number of CPUs in the Xtensa
+architecture family. It is, however, not feasible to support individual
+Xtensa CPUs in U-Boot. Therefore, there is only a single 'xtensa' CPU
+in the cpu tree of U-Boot.
+
+In the same manner as the Linux port to Xtensa, U-Boot adapts to an
+individual Xtensa core configuration using a set of macros provided with
+the particular core. This is part of what is known as the hardware
+abstraction layer (HAL). For the purpose of U-Boot, the HAL consists only
+of a few header files. These provide CPP macros that customize sources,
+Makefiles, and the linker script.
+
+
+Adding support for an additional processor configuration
+--------------------------------------------------------
+
+The header files for one particular processor configuration are inside
+a variant specific directory located in the arch/xtensa/include/asm
+directory. The name of that directory starts with 'arch-' followed by
+the name for the processor configuration, for example, arch-dc233c for
+the Diamond DC233 processor.
+
+ core.h Definitions for the core itself.
+
+The following files are part of the overlay but not used by U-Boot.
+
+ tie.h Co-processors and custom extensions defined
+ in the Tensilica Instruction Extension (TIE)
+ language.
+ tie-asm.h Assembly macros to access custom-defined registers
+ and states.
+
+
+Global Data Pointer, Exported Function Stubs, and the ABI
+---------------------------------------------------------
+
+To support standalone applications launched with the "go" command,
+U-Boot provides a jump table of entrypoints to exported functions
+(grep for EXPORT_FUNC). The implementation for Xtensa depends on
+which ABI (or function calling convention) is used.
+
+Call0 ABI is very conventional, and like most other architectures
+maintains the global data pointer gd in a register. This is chosen
+to be a14 because it is callee-saved (not clobbered) and has no
+other special use.
+
+Windowed ABI presents unique difficulties with the above approach.
+Because the register window rotates during a call, there is no
+register that is constantly available for the global data pointer.
+Therefore, a global variable is used in the same manner as i386.
+Another difficulty arises from the requirement to have an 'entry'
+at the beginning of a function, which rotates the register file and
+reserves a stack frame. This is an integral part of the windowed ABI
+implemented in hardware. It makes using a jump table to an arbitrary
+(separately compiled) function a bit tricky. Use of a simple wrapper
+is also very tedious due to the need to move all possible register
+arguments and adjust the stack to handle arguments that cannot be
+passed in registers. The most efficient approach is to have the jump
+table perform the 'entry' so as to pretend it's the start of the
+real function. This requires decoding the target function's 'entry'
+instruction to determine the stack frame size, and adjusting the stack
+pointer accordingly, then jumping into the target function just after
+the 'entry'. Decoding depends on the processor's endianness so uses
+the HAL. The implementation (12 instructions) is in examples/stubs.c .
+
+
+Access to Invalid Memory Addresses
+----------------------------------
+
+U-Boot does not check if memory addresses given as arguments to commands
+such as "md" are valid. The expectation appears to be that if the user
+requests to look at invalid memory he should expect to see garbage, and
+writes to invalid memory should be ignored.
+
+On many processors, and indeed many Xtensa configurations, this is
+acceptable. However on some configurations (particularly those with an
+MMU such as would be used with Linux) an exception is generated for an
+invalid memory access, which results in a hang if not handled.
+
+U-Boot for Xtensa provides a special memory exception handler to prevent
+hanging. The memory exception handler simply skips over the offending
+instruction. It is called for all memory exception causes that might
+be triggered by bad user input. While this is simplistic, it's better
+than hanging in most cases, while keeping U-Boot small and simple.
+
+
+------------------------------------------------------------------------------
+Chris Zankel
+Ross Morley
diff --git a/examples/standalone/stubs.c b/examples/standalone/stubs.c
index c5c025d..c26476d 100644
--- a/examples/standalone/stubs.c
+++ b/examples/standalone/stubs.c
@@ -223,6 +223,51 @@ gd_t *global_data;
" ld r10, [r10, %1]\n" \
" j [r10]\n" \
: : "i"(offsetof(gd_t, jt)), "i"(XF_ ## x * sizeof(void *)) : "r10");
+#elif defined(CONFIG_XTENSA)
+/*
+ * Call0 ABI: Global data ptr is in a14, and a8 is clobberable scratch.
+ * Windowed ABI: Global data ptr is in global_data, jump table ptr is in jt.
+ * Jump just past 'entry' in target and adjust stack frame
+ * (extract stack frame size from target 'entry' instruction).
+ */
+
+#ifdef __XTENSA_CALL0_ABI__
+#define EXPORT_FUNC(x) \
+ asm volatile ( \
+" .globl " #x "\n" \
+" .align 4\n" \
+#x ":\n" \
+" l32i a8, a14, %0\n" \
+" l32i a8, a8, %1\n" \
+" jx a8\n" \
+ : : "i" (offsetof(gd_t, jt)), "i" (XF_ ## x * sizeof(void *)) : "a8");
+#else
+
+static void **jt;
+#if XCHAL_HAVE_BE
+# define SFT "8"
+#else
+# define SFT "12"
+#endif
+#define EXPORT_FUNC(x) \
+ asm volatile ( \
+" .extern jt\n" \
+" .globl " #x "\n" \
+" .align 4\n" \
+#x ":\n" \
+" entry sp, 16\n" \
+" l32i a8, %0, 0\n" \
+" l32i a8, a8, %1\n" \
+" l32i a9, a8, 0\n" \
+" extui a9, a9, " SFT ", 12\n" \
+" subx8 a9, a9, sp\n" \
+" movi a10, 16\n" \
+" sub a9, a10, a9\n" \
+" movsp sp, a9\n" \
+" addi a8, a8, 3\n" \
+" jx a8\n" \
+ : : "r"(jt), "i" (XF_ ## x * sizeof(void *)) : "a8", "a9", "a10");
+#endif /* __XTENSA_CALL0_ABI__ */
#else
/*" addi $sp, $sp, -24\n" \
" br $r16\n" \*/
diff --git a/include/image.h b/include/image.h
index 3e8f78d..00b3fb5 100644
--- a/include/image.h
+++ b/include/image.h
@@ -173,6 +173,7 @@ struct lmb;
#define IH_ARCH_OPENRISC 21 /* OpenRISC 1000 */
#define IH_ARCH_ARM64 22 /* ARM64 */
#define IH_ARCH_ARC 23 /* Synopsys DesignWare ARC */
+#define IH_ARCH_XTENSA 24 /* Xtensa */
/*
* Image Types
diff --git a/include/linux/stat.h b/include/linux/stat.h
index cef6369..1af0876 100644
--- a/include/linux/stat.h
+++ b/include/linux/stat.h
@@ -126,7 +126,7 @@ struct stat {
#endif /* __MIPS__ */
-#if defined(__AVR32__) || defined(__SH__)
+#if defined(__AVR32__) || defined(__SH__) || defined(__XTENSA__)
struct stat {
unsigned long st_dev;
@@ -149,7 +149,7 @@ struct stat {
unsigned long __unused5;
};
-#endif /* __AVR32__ || __SH__ */
+#endif /* __AVR32__ || __SH__ || __XTENSA__ */
#ifdef __cplusplus
}
--
1.8.1.4
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