[PATCH] MIPS: Fix support for Cavium Octeon debugger stub.

[David Daney <ddaney@caviumnetworks.com>]

The Cavium Octeon bootloader has a debugger stub that requires a
little help from the target application to break in.

If configured, when we get an interrupt on the debug uart we wake up
the debugger.

Signed-off-by: David Daney <ddaney@caviumnetworks.com>
---
 arch/mips/Kconfig.debug               |   10 ++++++
 arch/mips/cavium-octeon/serial.c      |   53 ++++++++++++++++++++++++++++++++-
 arch/mips/cavium-octeon/setup.c       |    2 +-
 arch/mips/include/asm/octeon/octeon.h |    1 -
 4 files changed, 63 insertions(+), 3 deletions(-)

diff --git a/arch/mips/Kconfig.debug b/arch/mips/Kconfig.debug
index 364ca89..f6a0e68 100644
--- a/arch/mips/Kconfig.debug
+++ b/arch/mips/Kconfig.debug
@@ -42,6 +42,16 @@ config SB1XXX_CORELIS
          Select compile flags that produce code that can be processed by the
          Corelis mksym utility and UDB Emulator.
 
+config CAVIUM_GDB
+       bool "Remote GDB debugging using the Cavium Networks Multicore GDB"
+       depends on DEBUG_KERNEL
+       depends on CPU_CAVIUM_OCTEON
+       select DEBUG_INFO
+       help
+         If you say Y here, it will be possible to remotely debug the MIPS
+         kernel using the Cavium Networks GDB with extended SMP support.
+         This is only useful for kernel hackers. If unsure, say N.
+
 config RUNTIME_DEBUG
        bool "Enable run-time debugging"
        depends on DEBUG_KERNEL
diff --git a/arch/mips/cavium-octeon/serial.c b/arch/mips/cavium-octeon/serial.c
index 8240728..2110e68 100644
--- a/arch/mips/cavium-octeon/serial.c
+++ b/arch/mips/cavium-octeon/serial.c
@@ -18,11 +18,60 @@
 
 #include <asm/octeon/octeon.h>
 
+#if defined(CONFIG_CAVIUM_GDB)
+
 #ifdef CONFIG_GDB_CONSOLE
 #define DEBUG_UART 0
 #else
 #define DEBUG_UART 1
 #endif
+static irqreturn_t interrupt_debug_char(int cpl, void *dev_id)
+{
+       unsigned long lsrval;
+       unsigned long tmp;
+
+       lsrval = cvmx_read_csr(CVMX_MIO_UARTX_LSR(DEBUG_UART));
+       if (lsrval & 1) {
+#ifdef CONFIG_KGDB
+               /*
+                * The Cavium EJTAG bootmonitor stub is not compatible
+                * with KGDB.  We should never get here.
+                */
+#error Illegal to use both CONFIG_KGDB and CONFIG_CAVIUM_GDB
+#endif
+               /*
+                * Pulse MCD0 signal on Ctrl-C to stop all the
+                * cores. Also set the MCD0 to be not masked by this
+                * core so we know the signal is received by
+                * someone.
+                */
+               octeon_write_lcd("brk");
+               asm volatile ("dmfc0 %0, $22\n\t"
+                             "ori   %0, %0, 0x10\n\t"
+                             "dmtc0 %0, $22" : "=r" (tmp));
+               octeon_write_lcd("");
+               return IRQ_HANDLED;
+       }
+       return IRQ_NONE;
+}
+
+/* Enable uart1 interrupts for debugger Control-C processing */
+
+static int octeon_setup_debug_uart(void)
+{
+       if (request_irq(OCTEON_IRQ_UART0 + DEBUG_UART, interrupt_debug_char,
+                       IRQF_SHARED, "KGDB", interrupt_debug_char)) {
+               panic("request_irq(%d) failed.", OCTEON_IRQ_UART0 + DEBUG_UART);
+       }
+       cvmx_write_csr(CVMX_MIO_UARTX_IER(DEBUG_UART),
+                      cvmx_read_csr(CVMX_MIO_UARTX_IER(DEBUG_UART)) | 1);
+       return 0;
+}
+
+/* Install this as early as possible to be able to debug the boot
+   sequence.  */
+core_initcall(octeon_setup_debug_uart);
+#endif /* CONFIG_CAVIUM_GDB */
 
 unsigned int octeon_serial_in(struct uart_port *up, int offset)
 {
@@ -97,7 +146,9 @@ static int __init octeon_serial_init(void)
        enable_uart1 = 1;
 #endif
 #endif
-
+#ifdef CONFIG_CAVIUM_GDB
+       enable_uart1 = 0;
+#endif
        /* Right now CN52XX is the only chip with a third uart */
        enable_uart2 = OCTEON_IS_MODEL(OCTEON_CN52XX);
 
diff --git a/arch/mips/cavium-octeon/setup.c b/arch/mips/cavium-octeon/setup.c
index e195ea8..bc0c869 100644
--- a/arch/mips/cavium-octeon/setup.c
+++ b/arch/mips/cavium-octeon/setup.c
@@ -608,7 +608,7 @@ void __init prom_init(void)
         * When debugging the linux kernel, force the cores to enter
         * the debug exception handler to break in.
         */
-       if (octeon_get_boot_debug_flag()) {
+       if (octeon_boot_desc_ptr->flags & OCTEON_BL_FLAG_DEBUG) {
                cvmx_write_csr(CVMX_CIU_DINT, 1 << cvmx_get_core_num());
                cvmx_read_csr(CVMX_CIU_DINT);
        }
diff --git a/arch/mips/include/asm/octeon/octeon.h 
b/arch/mips/include/asm/octeon/octeon.h
index cac9b1a..f3c2b15 100644
--- a/arch/mips/include/asm/octeon/octeon.h
+++ b/arch/mips/include/asm/octeon/octeon.h
@@ -214,7 +214,6 @@ struct octeon_cf_data {
 
 extern void octeon_write_lcd(const char *s);
 extern void octeon_check_cpu_bist(void);
-extern int octeon_get_boot_debug_flag(void);
 extern int octeon_get_boot_uart(void);
 
 struct uart_port;
-- 
1.6.0.6