bmips: backport upstreamed RAC patches

Replace downstream bmips RAC fixes with upstream patches.

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
[backport upstream patches]
Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
This commit is contained in:
Christian Marangi 2024-06-25 11:19:41 +02:00 committed by Álvaro Fernández Rojas
parent 173d59e7dc
commit 7c9644a7b5
10 changed files with 386 additions and 132 deletions

View File

@ -42,6 +42,7 @@
cpus {
#address-cells = <1>;
#size-cells = <0>;
mips-cbr-reg = <0xff400000>;
mips-hpt-frequency = <150000000>;
cpu@0 {

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@ -43,6 +43,7 @@
cpus {
#address-cells = <1>;
#size-cells = <0>;
mips-cbr-reg = <0xff400000>;
mips-hpt-frequency = <200000000>;
cpu@0 {

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@ -0,0 +1,35 @@
From ce5cdd3b05216b704a704f466fb4c2dff3778caf Mon Sep 17 00:00:00 2001
From: Christian Marangi <ansuelsmth@gmail.com>
Date: Tue, 11 Jun 2024 13:35:33 +0200
Subject: [PATCH] mips: bmips: BCM6358: make sure CBR is correctly set
It was discovered that some device have CBR address set to 0 causing
kernel panic when arch_sync_dma_for_cpu_all is called.
This was notice in situation where the system is booted from TP1 and
BMIPS_GET_CBR() returns 0 instead of a valid address and
!!(read_c0_brcm_cmt_local() & (1 << 31)); not failing.
The current check whether RAC flush should be disabled or not are not
enough hence lets check if CBR is a valid address or not.
Fixes: ab327f8acdf8 ("mips: bmips: BCM6358: disable RAC flush for TP1")
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
Acked-by: Florian Fainelli <florian.fainelli@broadcom.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
---
arch/mips/bmips/setup.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
--- a/arch/mips/bmips/setup.c
+++ b/arch/mips/bmips/setup.c
@@ -110,7 +110,8 @@ static void bcm6358_quirks(void)
* RAC flush causes kernel panics on BCM6358 when booting from TP1
* because the bootloader is not initializing it properly.
*/
- bmips_rac_flush_disable = !!(read_c0_brcm_cmt_local() & (1 << 31));
+ bmips_rac_flush_disable = !!(read_c0_brcm_cmt_local() & (1 << 31)) ||
+ !!BMIPS_GET_CBR();
}
static void bcm6368_quirks(void)

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@ -0,0 +1,171 @@
From a5c05453a13ab324ad8719e8a23dfb6af01f3652 Mon Sep 17 00:00:00 2001
From: Christian Marangi <ansuelsmth@gmail.com>
Date: Thu, 20 Jun 2024 17:26:42 +0200
Subject: [PATCH 1/4] mips: bmips: rework and cache CBR addr handling
Rework the handling of the CBR address and cache it. This address
doesn't change and can be cached instead of reading the register every
time.
This is in preparation of permitting to tweak the CBR address in DT with
broken SoC or bootloader.
bmips_cbr_addr is defined in setup.c for each arch to keep compatibility
with legacy brcm47xx/brcm63xx and generic BMIPS target.
Acked-by: Florian Fainelli <florian.fainelli@broadcom.com>
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
---
arch/mips/bcm47xx/prom.c | 3 +++
arch/mips/bcm47xx/setup.c | 4 ++++
arch/mips/bcm63xx/prom.c | 3 +++
arch/mips/bcm63xx/setup.c | 4 ++++
arch/mips/bmips/dma.c | 2 +-
arch/mips/bmips/setup.c | 7 ++++++-
arch/mips/include/asm/bmips.h | 1 +
arch/mips/kernel/smp-bmips.c | 4 ++--
8 files changed, 24 insertions(+), 4 deletions(-)
--- a/arch/mips/bcm47xx/prom.c
+++ b/arch/mips/bcm47xx/prom.c
@@ -32,6 +32,7 @@
#include <linux/ssb/ssb_driver_chipcommon.h>
#include <linux/ssb/ssb_regs.h>
#include <linux/smp.h>
+#include <asm/bmips.h>
#include <asm/bootinfo.h>
#include <bcm47xx.h>
#include <bcm47xx_board.h>
@@ -109,6 +110,8 @@ static __init void prom_init_mem(void)
void __init prom_init(void)
{
+ /* Cache CBR addr before CPU/DMA setup */
+ bmips_cbr_addr = BMIPS_GET_CBR();
prom_init_mem();
setup_8250_early_printk_port(CKSEG1ADDR(BCM47XX_SERIAL_ADDR), 0, 0);
}
--- a/arch/mips/bcm47xx/setup.c
+++ b/arch/mips/bcm47xx/setup.c
@@ -37,6 +37,7 @@
#include <linux/ssb/ssb.h>
#include <linux/ssb/ssb_embedded.h>
#include <linux/bcma/bcma_soc.h>
+#include <asm/bmips.h>
#include <asm/bootinfo.h>
#include <asm/idle.h>
#include <asm/prom.h>
@@ -45,6 +46,9 @@
#include <bcm47xx.h>
#include <bcm47xx_board.h>
+/* CBR addr doesn't change and we can cache it */
+void __iomem *bmips_cbr_addr __read_mostly;
+
union bcm47xx_bus bcm47xx_bus;
EXPORT_SYMBOL(bcm47xx_bus);
--- a/arch/mips/bcm63xx/prom.c
+++ b/arch/mips/bcm63xx/prom.c
@@ -22,6 +22,9 @@ void __init prom_init(void)
{
u32 reg, mask;
+ /* Cache CBR addr before CPU/DMA setup */
+ bmips_cbr_addr = BMIPS_GET_CBR();
+
bcm63xx_cpu_init();
/* stop any running watchdog */
--- a/arch/mips/bcm63xx/setup.c
+++ b/arch/mips/bcm63xx/setup.c
@@ -12,6 +12,7 @@
#include <linux/memblock.h>
#include <linux/ioport.h>
#include <linux/pm.h>
+#include <asm/bmips.h>
#include <asm/bootinfo.h>
#include <asm/time.h>
#include <asm/reboot.h>
@@ -22,6 +23,9 @@
#include <bcm63xx_io.h>
#include <bcm63xx_gpio.h>
+/* CBR addr doesn't change and we can cache it */
+void __iomem *bmips_cbr_addr __read_mostly;
+
void bcm63xx_machine_halt(void)
{
pr_info("System halted\n");
--- a/arch/mips/bmips/dma.c
+++ b/arch/mips/bmips/dma.c
@@ -9,7 +9,7 @@ bool bmips_rac_flush_disable;
void arch_sync_dma_for_cpu_all(void)
{
- void __iomem *cbr = BMIPS_GET_CBR();
+ void __iomem *cbr = bmips_cbr_addr;
u32 cfg;
if (boot_cpu_type() != CPU_BMIPS3300 &&
--- a/arch/mips/bmips/setup.c
+++ b/arch/mips/bmips/setup.c
@@ -34,6 +34,9 @@
#define REG_BCM6328_OTP ((void __iomem *)CKSEG1ADDR(0x1000062c))
#define BCM6328_TP1_DISABLED BIT(9)
+/* CBR addr doesn't change and we can cache it */
+void __iomem *bmips_cbr_addr __read_mostly;
+
extern bool bmips_rac_flush_disable;
static const unsigned long kbase = VMLINUX_LOAD_ADDRESS & 0xfff00000;
@@ -111,7 +114,7 @@ static void bcm6358_quirks(void)
* because the bootloader is not initializing it properly.
*/
bmips_rac_flush_disable = !!(read_c0_brcm_cmt_local() & (1 << 31)) ||
- !!BMIPS_GET_CBR();
+ !!bmips_cbr_addr;
}
static void bcm6368_quirks(void)
@@ -144,6 +147,8 @@ static void __init bmips_init_cfe(void)
void __init prom_init(void)
{
+ /* Cache CBR addr before CPU/DMA setup */
+ bmips_cbr_addr = BMIPS_GET_CBR();
bmips_init_cfe();
bmips_cpu_setup();
register_bmips_smp_ops();
--- a/arch/mips/include/asm/bmips.h
+++ b/arch/mips/include/asm/bmips.h
@@ -81,6 +81,7 @@ extern char bmips_smp_movevec[];
extern char bmips_smp_int_vec[];
extern char bmips_smp_int_vec_end[];
+extern void __iomem *bmips_cbr_addr;
extern int bmips_smp_enabled;
extern int bmips_cpu_offset;
extern cpumask_t bmips_booted_mask;
--- a/arch/mips/kernel/smp-bmips.c
+++ b/arch/mips/kernel/smp-bmips.c
@@ -518,7 +518,7 @@ static void bmips_set_reset_vec(int cpu,
info.val = val;
bmips_set_reset_vec_remote(&info);
} else {
- void __iomem *cbr = BMIPS_GET_CBR();
+ void __iomem *cbr = bmips_cbr_addr;
if (cpu == 0)
__raw_writel(val, cbr + BMIPS_RELO_VECTOR_CONTROL_0);
@@ -591,7 +591,7 @@ asmlinkage void __weak plat_wired_tlb_se
void bmips_cpu_setup(void)
{
- void __iomem __maybe_unused *cbr = BMIPS_GET_CBR();
+ void __iomem __maybe_unused *cbr = bmips_cbr_addr;
u32 __maybe_unused cfg;
switch (current_cpu_type()) {

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@ -0,0 +1,111 @@
From b95b30e50aed225d26e20737873ae2404941901c Mon Sep 17 00:00:00 2001
From: Christian Marangi <ansuelsmth@gmail.com>
Date: Thu, 20 Jun 2024 17:26:44 +0200
Subject: [PATCH 3/4] mips: bmips: setup: make CBR address configurable
Add support to provide CBR address from DT to handle broken
SoC/Bootloader that doesn't correctly init it. This permits to use the
RAC flush even in these condition.
To provide a CBR address from DT, the property "brcm,bmips-cbr-reg"
needs to be set in the "cpus" node. On DT init, this property presence
will be checked and will set the bmips_cbr_addr value accordingly. Also
bmips_rac_flush_disable will be set to false as RAC flush can be
correctly supported.
The CBR address from DT will overwrite the cached one and the
one set in the CBR register will be ignored.
Also the DT CBR address is validated on being outside DRAM window.
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
Acked-by: Florian Fainelli <florian.fainelli@broadcom.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
---
arch/mips/bcm47xx/setup.c | 6 +++++-
arch/mips/bcm63xx/setup.c | 6 +++++-
arch/mips/bmips/setup.c | 30 ++++++++++++++++++++++++++++--
3 files changed, 38 insertions(+), 4 deletions(-)
--- a/arch/mips/bcm47xx/setup.c
+++ b/arch/mips/bcm47xx/setup.c
@@ -46,7 +46,11 @@
#include <bcm47xx.h>
#include <bcm47xx_board.h>
-/* CBR addr doesn't change and we can cache it */
+/*
+ * CBR addr doesn't change and we can cache it.
+ * For broken SoC/Bootloader CBR addr might also be provided via DT
+ * with "brcm,bmips-cbr-reg" in the "cpus" node.
+ */
void __iomem *bmips_cbr_addr __read_mostly;
union bcm47xx_bus bcm47xx_bus;
--- a/arch/mips/bcm63xx/setup.c
+++ b/arch/mips/bcm63xx/setup.c
@@ -23,7 +23,11 @@
#include <bcm63xx_io.h>
#include <bcm63xx_gpio.h>
-/* CBR addr doesn't change and we can cache it */
+/*
+ * CBR addr doesn't change and we can cache it.
+ * For broken SoC/Bootloader CBR addr might also be provided via DT
+ * with "brcm,bmips-cbr-reg" in the "cpus" node.
+ */
void __iomem *bmips_cbr_addr __read_mostly;
void bcm63xx_machine_halt(void)
--- a/arch/mips/bmips/setup.c
+++ b/arch/mips/bmips/setup.c
@@ -34,7 +34,11 @@
#define REG_BCM6328_OTP ((void __iomem *)CKSEG1ADDR(0x1000062c))
#define BCM6328_TP1_DISABLED BIT(9)
-/* CBR addr doesn't change and we can cache it */
+/*
+ * CBR addr doesn't change and we can cache it.
+ * For broken SoC/Bootloader CBR addr might also be provided via DT
+ * with "brcm,bmips-cbr-reg" in the "cpus" node.
+ */
void __iomem *bmips_cbr_addr __read_mostly;
extern bool bmips_rac_flush_disable;
@@ -208,13 +212,35 @@ void __init plat_mem_setup(void)
void __init device_tree_init(void)
{
struct device_node *np;
+ u32 addr;
unflatten_and_copy_device_tree();
/* Disable SMP boot unless both CPUs are listed in DT and !disabled */
np = of_find_node_by_name(NULL, "cpus");
- if (np && of_get_available_child_count(np) <= 1)
+ if (!np)
+ return;
+
+ if (of_get_available_child_count(np) <= 1)
bmips_smp_enabled = 0;
+
+ /* Check if DT provide a CBR address */
+ if (of_property_read_u32(np, "brcm,bmips-cbr-reg", &addr))
+ goto exit;
+
+ /* Make sure CBR address is outside DRAM window */
+ if (addr >= (u32)memblock_start_of_DRAM() &&
+ addr < (u32)memblock_end_of_DRAM()) {
+ WARN(1, "DT CBR %x inside DRAM window. Ignoring DT CBR.\n",
+ addr);
+ goto exit;
+ }
+
+ bmips_cbr_addr = (void __iomem *)addr;
+ /* Since CBR is provided by DT, enable RAC flush */
+ bmips_rac_flush_disable = false;
+
+exit:
of_node_put(np);
}

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@ -0,0 +1,57 @@
From 04f38d1a4db017f17e82442727b91ce03dd72759 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Daniel=20Gonz=C3=A1lez=20Cabanelas?= <dgcbueu@gmail.com>
Date: Thu, 20 Jun 2024 17:26:45 +0200
Subject: [PATCH 4/4] mips: bmips: enable RAC on BMIPS4350
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
The data RAC is left disabled by the bootloader in some SoCs, at least in
the core it boots from.
Enabling this feature increases the performance up to +30% depending on the
task.
Signed-off-by: Daniel González Cabanelas <dgcbueu@gmail.com>
Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
[ rework code and reduce code duplication ]
Acked-by: Florian Fainelli <florian.fainelli@broadcom.com>
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
---
arch/mips/kernel/smp-bmips.c | 18 ++++++++++++++++++
1 file changed, 18 insertions(+)
--- a/arch/mips/kernel/smp-bmips.c
+++ b/arch/mips/kernel/smp-bmips.c
@@ -592,6 +592,7 @@ asmlinkage void __weak plat_wired_tlb_se
void bmips_cpu_setup(void)
{
void __iomem __maybe_unused *cbr = bmips_cbr_addr;
+ u32 __maybe_unused rac_addr;
u32 __maybe_unused cfg;
switch (current_cpu_type()) {
@@ -620,6 +621,23 @@ void bmips_cpu_setup(void)
__raw_readl(cbr + BMIPS_RAC_ADDRESS_RANGE);
break;
+ case CPU_BMIPS4350:
+ rac_addr = BMIPS_RAC_CONFIG_1;
+
+ if (!(read_c0_brcm_cmt_local() & (1 << 31)))
+ rac_addr = BMIPS_RAC_CONFIG;
+
+ /* Enable data RAC */
+ cfg = __raw_readl(cbr + rac_addr);
+ __raw_writel(cfg | 0xf, cbr + rac_addr);
+ __raw_readl(cbr + rac_addr);
+
+ /* Flush stale data out of the readahead cache */
+ cfg = __raw_readl(cbr + BMIPS_RAC_CONFIG);
+ __raw_writel(cfg | 0x100, cbr + BMIPS_RAC_CONFIG);
+ __raw_readl(cbr + BMIPS_RAC_CONFIG);
+ break;
+
case CPU_BMIPS4380:
/* CBG workaround for early BMIPS4380 CPUs */
switch (read_c0_prid()) {

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@ -15,7 +15,7 @@ Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
--- a/arch/mips/bmips/setup.c
+++ b/arch/mips/bmips/setup.c
@@ -31,13 +31,52 @@
@@ -31,8 +31,42 @@
#define RELO_NORMAL_VEC BIT(18)
@ -56,7 +56,9 @@ Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
+#define BCM63268_FCVO_SHIFT 21
+#define BCM63268_FCVO_MASK (0xf << BCM63268_FCVO_SHIFT)
extern bool bmips_rac_flush_disable;
/*
* CBR addr doesn't change and we can cache it.
@@ -45,6 +79,11 @@ extern bool bmips_rac_flush_disable;
static const unsigned long kbase = VMLINUX_LOAD_ADDRESS & 0xfff00000;
@ -68,7 +70,7 @@ Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
struct bmips_quirk {
const char *compatible;
void (*quirk_fn)(void);
@@ -153,17 +192,161 @@ const char *get_system_type(void)
@@ -163,17 +202,161 @@ const char *get_system_type(void)
return "Generic BMIPS kernel";
}

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@ -70,9 +70,9 @@ Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
+
+#define DDR_CSEND_REG 0x8
extern bool bmips_rac_flush_disable;
@@ -77,6 +98,11 @@ struct bmips_cpufreq {
/*
* CBR addr doesn't change and we can cache it.
@@ -84,6 +105,11 @@ struct bmips_cpufreq {
u32 (*cpu_freq)(void);
};
@ -84,7 +84,7 @@ Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
struct bmips_quirk {
const char *compatible;
void (*quirk_fn)(void);
@@ -351,9 +377,90 @@ void __init plat_time_init(void)
@@ -361,9 +387,90 @@ void __init plat_time_init(void)
mips_hpt_frequency = freq;
}
@ -175,7 +175,7 @@ Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
const struct bmips_quirk *q;
set_io_port_base(0);
@@ -374,6 +481,18 @@ void __init plat_mem_setup(void)
@@ -384,6 +491,18 @@ void __init plat_mem_setup(void)
__dt_setup_arch(dtb);

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@ -1,82 +0,0 @@
From 3e4c3863e0cfb8c2abdff6bb494ca69d3d2aed9c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=81lvaro=20Fern=C3=A1ndez=20Rojas?= <noltari@gmail.com>
Date: Sat, 10 Jun 2023 17:01:40 +0200
Subject: [PATCH] mips: bmips: dma: fix CBR address
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Some BCM63xx SoCs may return CBR address as 0.
Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
---
arch/mips/bmips/dma.c | 12 ++++--------
arch/mips/bmips/setup.c | 11 ++++-------
2 files changed, 8 insertions(+), 15 deletions(-)
--- a/arch/mips/bmips/dma.c
+++ b/arch/mips/bmips/dma.c
@@ -5,11 +5,10 @@
#include <asm/bmips.h>
#include <asm/io.h>
-bool bmips_rac_flush_disable;
+void __iomem *bmips_cbr_addr;
void arch_sync_dma_for_cpu_all(void)
{
- void __iomem *cbr = BMIPS_GET_CBR();
u32 cfg;
if (boot_cpu_type() != CPU_BMIPS3300 &&
@@ -17,11 +16,8 @@ void arch_sync_dma_for_cpu_all(void)
boot_cpu_type() != CPU_BMIPS4380)
return;
- if (unlikely(bmips_rac_flush_disable))
- return;
-
/* Flush stale data out of the readahead cache */
- cfg = __raw_readl(cbr + BMIPS_RAC_CONFIG);
- __raw_writel(cfg | 0x100, cbr + BMIPS_RAC_CONFIG);
- __raw_readl(cbr + BMIPS_RAC_CONFIG);
+ cfg = __raw_readl(bmips_cbr_addr + BMIPS_RAC_CONFIG);
+ __raw_writel(cfg | 0x100, bmips_cbr_addr + BMIPS_RAC_CONFIG);
+ __raw_readl(bmips_cbr_addr + BMIPS_RAC_CONFIG);
}
--- a/arch/mips/bmips/setup.c
+++ b/arch/mips/bmips/setup.c
@@ -89,7 +89,7 @@
#define DDR_CSEND_REG 0x8
-extern bool bmips_rac_flush_disable;
+extern void __iomem *bmips_cbr_addr;
static const unsigned long kbase = VMLINUX_LOAD_ADDRESS & 0xfff00000;
@@ -170,12 +170,6 @@ static void bcm6358_quirks(void)
* disable SMP for now
*/
bmips_smp_enabled = 0;
-
- /*
- * RAC flush causes kernel panics on BCM6358 when booting from TP1
- * because the bootloader is not initializing it properly.
- */
- bmips_rac_flush_disable = !!(read_c0_brcm_cmt_local() & (1 << 31));
}
static void bcm6368_quirks(void)
@@ -208,6 +202,11 @@ static void __init bmips_init_cfe(void)
void __init prom_init(void)
{
+ if (!(read_c0_brcm_cbr() >> 18))
+ bmips_cbr_addr = (void __iomem *) 0xff400000;
+ else
+ bmips_cbr_addr = BMIPS_GET_CBR();
+
bmips_init_cfe();
bmips_cpu_setup();
register_bmips_smp_ops();

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@ -1,42 +0,0 @@
From 7f862eaedac56b67972393f0a9affcd2fe53479b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Daniel=20Gonz=C3=A1lez=20Cabanelas?= <dgcbueu@gmail.com>
Date: Sun, 18 Jun 2023 19:59:25 +0200
Subject: [PATCH] mips: bmips: enable RAC on BMIPS4350
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
The data RAC is left disabled by the bootloader in some SoCs, at least in
the core it boots from.
Enabling this feature increases the performance up to +30% depending on the
task.
Signed-off-by: Daniel González Cabanelas <dgcbueu@gmail.com>
Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
---
arch/mips/kernel/smp-bmips.c | 14 ++++++++++++++
1 file changed, 14 insertions(+)
--- a/arch/mips/kernel/smp-bmips.c
+++ b/arch/mips/kernel/smp-bmips.c
@@ -620,6 +620,20 @@ void bmips_cpu_setup(void)
__raw_readl(cbr + BMIPS_RAC_ADDRESS_RANGE);
break;
+ case CPU_BMIPS4350:
+ /* Enable data RAC */
+ if (!(read_c0_brcm_cmt_local() & (1 << 31))) {
+ cfg = __raw_readl(cbr + BMIPS_RAC_CONFIG);
+ __raw_writel(cfg | 0xa, cbr + BMIPS_RAC_CONFIG);
+ __raw_readl(cbr + BMIPS_RAC_CONFIG);
+ } else {
+ cbr = (void __iomem *)0xff400000;
+ cfg = __raw_readl(cbr + BMIPS_RAC_CONFIG_1);
+ __raw_writel(cfg | 0xa, cbr + BMIPS_RAC_CONFIG_1);
+ __raw_readl(cbr + BMIPS_RAC_CONFIG_1);
+ }
+ break;
+
case CPU_BMIPS4380:
/* CBG workaround for early BMIPS4380 CPUs */
switch (read_c0_prid()) {