arm_fpga: Add support for unknown MPIDs

This patch allows the system to fallback to a default CPU library
in case the MPID does not match with any of the supported ones.

This feature can be enabled by setting SUPPORT_UNKNOWN_MPID build
option to 1 (enabled by default only on arm_fpga platform).

This feature can be very dangerous on a production image and
therefore it MUST be disabled for Release images.

Signed-off-by: Javier Almansa Sobrino <javier.almansasobrino@arm.com>
Change-Id: I0df7ef2b012d7d60a4fd5de44dea1fbbb46881ba

bl31/bl31.mk

@@ -7,6 +7,12 @@
 ################################################################################
 # Include Makefile for the SPM-MM implementation
 ################################################################################
+ifeq (${SUPPORT_UNKNOWN_MPID},1)
+  ifeq (${DEBUG},0)
+    $(warning WARNING: SUPPORT_UNKNOWN_MPID enabled)
+  endif
+endif
+
 ifeq (${SPM_MM},1)
   ifeq (${EL3_EXCEPTION_HANDLING},0)
     $(error EL3_EXCEPTION_HANDLING must be 1 for SPM-MM support)

bl31/bl31_main.c

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2013-2019, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2013-2020, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -41,6 +41,15 @@ static int32_t (*bl32_init)(void);
  ******************************************************************************/
 static uint32_t next_image_type = NON_SECURE;
 
+#ifdef SUPPORT_UNKNOWN_MPID
+/*
+ * Flag to know whether an unsupported MPID has been detected. To avoid having it
+ * landing on the .bss section, it is initialized to a non-zero value, this way
+ * we avoid potential WAW hazards during system bring up.
+ * */
+volatile uint32_t unsupported_mpid_flag = 1;
+#endif
+
 /*
  * Implement the ARM Standard Service function to get arguments for a
  * particular service.
@@ -98,6 +107,12 @@ void bl31_main(void)
 	NOTICE("BL31: %s\n", version_string);
 	NOTICE("BL31: %s\n", build_message);
 
+#ifdef SUPPORT_UNKNOWN_MPID
+	if (unsupported_mpid_flag == 0) {
+		NOTICE("Unsupported MPID detected!\n");
+	}
+#endif
+
 	/* Perform platform setup in BL31 */
 	bl31_platform_setup();
 

include/lib/cpus/aarch64/generic.h

@@ -0,0 +1,18 @@
+/*
+ * Copyright (c) 2020, Arm Limited. All rights reserverd.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#ifndef AARCH64_GENERIC_H
+#define AARCH64_GENERIC_H
+
+#include <lib/utils_def.h>
+
+/*
+ * 0x0 value on the MIDR implementer value is reserved for software use,
+ * so use an MIDR value of 0 for a default CPU library.
+ */
+#define AARCH64_GENERIC_MIDR			U(0)
+
+#endif /* AARCH64_GENERIC_H */

lib/cpus/aarch64/cpu_helpers.S

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2014-2019, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2014-2020, Arm Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -140,6 +140,13 @@ endfunc do_cpu_reg_dump
 	 * midr of the core. It reads the MIDR_EL1 and finds the matching
 	 * entry in cpu_ops entries. Only the implementation and part number
 	 * are used to match the entries.
+	 *
+	 * If cpu_ops for the MIDR_EL1 cannot be found and
+	 * SUPPORT_UNKNOWN_MPID is enabled, it will try to look for a
+	 * default cpu_ops with an MIDR value of 0.
+	 * (Implementation number 0x0 should be reseverd for software use
+	 * and therefore no clashes should happen with that default value).
+	 *
 	 * Return :
 	 *     x0 - The matching cpu_ops pointer on Success
 	 *     x0 - 0 on failure.
@@ -147,23 +154,26 @@ endfunc do_cpu_reg_dump
 	 */
 	.globl	get_cpu_ops_ptr
 func get_cpu_ops_ptr
-	/* Get the cpu_ops start and end locations */
-	adr	x4, (__CPU_OPS_START__ + CPU_MIDR)
-	adr	x5, (__CPU_OPS_END__ + CPU_MIDR)
-
-	/* Initialize the return parameter */
-	mov	x0, #0
-
 	/* Read the MIDR_EL1 */
 	mrs	x2, midr_el1
 	mov_imm	x3, CPU_IMPL_PN_MASK
 
 	/* Retain only the implementation and part number using mask */
 	and	w2, w2, w3
+
+	/* Get the cpu_ops end location */
+	adr	x5, (__CPU_OPS_END__ + CPU_MIDR)
+
+	/* Initialize the return parameter */
+	mov	x0, #0
 1:
+	/* Get the cpu_ops start location */
+	adr	x4, (__CPU_OPS_START__ + CPU_MIDR)
+
+2:
 	/* Check if we have reached end of list */
 	cmp	x4, x5
-	b.eq	error_exit
+	b.eq	search_def_ptr
 
 	/* load the midr from the cpu_ops */
 	ldr	x1, [x4], #CPU_OPS_SIZE
@@ -171,7 +181,7 @@ func get_cpu_ops_ptr
 
 	/* Check if midr matches to midr of this core */
 	cmp	w1, w2
-	b.ne	1b
+	b.ne	2b
 
 	/* Subtract the increment and offset to get the cpu-ops pointer */
 	sub	x0, x4, #(CPU_OPS_SIZE + CPU_MIDR)
@@ -179,7 +189,27 @@ func get_cpu_ops_ptr
 	cmp	x0, #0
 	ASM_ASSERT(ne)
 #endif
+#ifdef SUPPORT_UNKNOWN_MPID
+	cbnz	x2, exit_mpid_found
+	/* Mark the unsupported MPID flag */
+	adrp	x1, unsupported_mpid_flag
+	add	x1, x1, :lo12:unsupported_mpid_flag
+	str	w2, [x1]
+exit_mpid_found:
+#endif
+	ret
+
+	/*
+	 * Search again for a default pointer (MIDR = 0x0)
+	 * or return error if already searched.
+	 */
+search_def_ptr:
+#ifdef SUPPORT_UNKNOWN_MPID
+	cbz	x2, error_exit
+	mov	x2, #0
+	b	1b
 error_exit:
+#endif
 	ret
 endfunc get_cpu_ops_ptr
 

lib/cpus/aarch64/generic.S

@@ -0,0 +1,89 @@
+/*
+ * Copyright (c) 2020, Arm Limited. All rights reserved.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#include <arch.h>
+#include <asm_macros.S>
+#include <common/bl_common.h>
+#include <generic.h>
+#include <cpu_macros.S>
+#include <plat_macros.S>
+
+	/* ---------------------------------------------
+	 * Disable L1 data cache and unified L2 cache
+	 * ---------------------------------------------
+	 */
+func generic_disable_dcache
+	mrs	x1, sctlr_el3
+	bic	x1, x1, #SCTLR_C_BIT
+	msr	sctlr_el3, x1
+	isb
+	ret
+endfunc generic_disable_dcache
+
+func generic_core_pwr_dwn
+	mov	x18, x30
+
+	/* ---------------------------------------------
+	 * Turn off caches.
+	 * ---------------------------------------------
+	 */
+	bl	generic_disable_dcache
+
+	/* ---------------------------------------------
+	 * Flush L1 caches.
+	 * ---------------------------------------------
+	 */
+	mov	x0, #DCCISW
+	bl	dcsw_op_level1
+
+	ret	x18
+endfunc generic_core_pwr_dwn
+
+func generic_cluster_pwr_dwn
+	mov	x18, x30
+
+	/* ---------------------------------------------
+	 * Turn off caches.
+	 * ---------------------------------------------
+	 */
+	bl	generic_disable_dcache
+
+	/* ---------------------------------------------
+	 * Flush L1 caches.
+	 * ---------------------------------------------
+	 */
+	mov	x0, #DCCISW
+	bl	dcsw_op_level1
+
+	/* ---------------------------------------------
+	 * Disable the optional ACP.
+	 * ---------------------------------------------
+	 */
+	bl	plat_disable_acp
+
+	/* ---------------------------------------------
+	 * Flush L2 caches.
+	 * ---------------------------------------------
+	 */
+	mov	x0, #DCCISW
+	bl	dcsw_op_level2
+
+	ret	x18
+
+endfunc generic_cluster_pwr_dwn
+
+/* ---------------------------------------------
+ * Unimplemented functions.
+ * ---------------------------------------------
+ */
+.equ	generic_errata_report,		0
+.equ	generic_cpu_reg_dump,		0
+.equ	generic_reset_func,		0
+
+declare_cpu_ops generic, AARCH64_GENERIC_MIDR, \
+	generic_reset_func, \
+	generic_core_pwr_dwn, \
+	generic_cluster_pwr_dwn

plat/arm/board/arm_fpga/platform.mk

@@ -1,5 +1,5 @@
 #
-# Copyright (c) 2020, ARM Limited and Contributors. All rights reserved.
+# Copyright (c) 2020, Arm Limited. All rights reserved.
 #
 # SPDX-License-Identifier: BSD-3-Clause
 #
@@ -40,6 +40,8 @@ HW_ASSISTED_COHERENCY	:=	1
 
 PL011_GENERIC_UART	:=	1
 
+SUPPORT_UNKNOWN_MPID	?=	1
+
 FPGA_CPU_LIBS	:=	lib/cpus/${ARCH}/aem_generic.S
 
 # select a different set of CPU files, depending on whether we compile for
@@ -71,6 +73,12 @@ else
 				lib/cpus/aarch64/cortex_a75.S
 endif
 
+ifeq (${SUPPORT_UNKNOWN_MPID}, 1)
+# Add support for unknown/invalid MPIDs (aarch64 only)
+$(eval $(call add_define,SUPPORT_UNKNOWN_MPID))
+	FPGA_CPU_LIBS	+=	lib/cpus/aarch64/generic.S
+endif
+
 # Allow detection of GIC-600
 GICV3_SUPPORT_GIC600	:=	1