[POWERPC] Early serial debug support for PPC44x

This adds support for early serial debugging via the built in
port on IBM/AMCC PowerPC 44x CPUs.  It uses a bolted TLB entry in
address space 1 for the UART's mapping, allowing robust debugging both
before and after the initialization of the MMU.

Signed-off-by: David Gibson <dwg@au1.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>

7 files changed, 90 insertions, 26 deletions

diff --git a/arch/powerpc/Kconfig.debug b/arch/powerpc/Kconfig.debug
index 86aa3745af7f..f70e795c262e 100644
--- a/arch/powerpc/Kconfig.debug
+++ b/arch/powerpc/Kconfig.debug
@@ -139,10 +139,6 @@ config BOOTX_TEXT
           Say Y here to see progress messages from the boot firmware in text
           mode. Requires either BootX or Open Firmware.
 
-config SERIAL_TEXT_DEBUG
-        bool "Support for early boot texts over serial port"
-        depends on 4xx
-
 config PPC_EARLY_DEBUG
         bool "Early debugging (dangerous)"
 
@@ -207,6 +203,24 @@ config PPC_EARLY_DEBUG_BEAT
         help
           Select this to enable early debugging for Celleb with Beat.
 
+config PPC_EARLY_DEBUG_44x
+        bool "Early serial debugging for IBM/AMCC 44x CPUs"
+        depends on 44x
+        select PPC_UDBG_16550
+        help
+          Select this to enable early debugging for IBM 44x chips via the
+          inbuilt serial port.
+
 endchoice
 
+config PPC_EARLY_DEBUG_44x_PHYSLOW
+        hex "Low 32 bits of early debug UART physical address"
+        depends PPC_EARLY_DEBUG_44x
+        default "0x40000200"
+
+config PPC_EARLY_DEBUG_44x_PHYSHIGH
+        hex "EPRN of early debug UART physical address"
+        depends PPC_EARLY_DEBUG_44x
+        default "0x1"
+
 endmenu
diff --git a/arch/powerpc/kernel/head_44x.S b/arch/powerpc/kernel/head_44x.S
index a51026f0a9d7..88695963f587 100644
--- a/arch/powerpc/kernel/head_44x.S
+++ b/arch/powerpc/kernel/head_44x.S
@@ -172,36 +172,28 @@ skpinv:	addi	r4,r4,1				/* Increment */
         isync
 
 4:
-#ifdef CONFIG_SERIAL_TEXT_DEBUG
-        /*
-         * Add temporary UART mapping for early debug.
-         * We can map UART registers wherever we want as long as they don't
-         * interfere with other system mappings (e.g. with pinned entries).
-         * For an example of how we handle this - see ocotea.h.       --ebs
-         */
+#ifdef CONFIG_PPC_EARLY_DEBUG_44x
+        /* Add UART mapping for early debug. */
+
         /* pageid fields */
-        lis     r3,UART0_IO_BASE@h
-        ori     r3,r3,PPC44x_TLB_VALID | PPC44x_TLB_4K
+        lis     r3,PPC44x_EARLY_DEBUG_VIRTADDR@h
+        ori     r3,r3,PPC44x_TLB_VALID|PPC44x_TLB_TS|PPC44x_TLB_64K
 
         /* xlat fields */
-        lis     r4,UART0_PHYS_IO_BASE@h         /* RPN depends on SoC */
-#ifndef CONFIG_440EP
-        ori     r4,r4,0x0001            /* ERPN is 1 for second 4GB page */
-#endif
+        lis     r4,CONFIG_PPC_EARLY_DEBUG_44x_PHYSLOW@h
+        ori     r4,r4,CONFIG_PPC_EARLY_DEBUG_44x_PHYSHIGH
 
         /* attrib fields */
-        li      r5,0
-        ori     r5,r5,(PPC44x_TLB_SW | PPC44x_TLB_SR | PPC44x_TLB_I | PPC44x_TLB_G)
+        li      r5,(PPC44x_TLB_SW|PPC44x_TLB_SR|PPC44x_TLB_I|PPC44x_TLB_G)
+        li      r0,62                    /* TLB slot 0 */
 
-        li      r0,0                    /* TLB slot 0 */
-
-        tlbwe   r3,r0,PPC44x_TLB_PAGEID /* Load the pageid fields */
-        tlbwe   r4,r0,PPC44x_TLB_XLAT   /* Load the translation fields */
-        tlbwe   r5,r0,PPC44x_TLB_ATTRIB /* Load the attrib/access fields */
+        tlbwe   r3,r0,PPC44x_TLB_PAGEID
+        tlbwe   r4,r0,PPC44x_TLB_XLAT
+        tlbwe   r5,r0,PPC44x_TLB_ATTRIB
 
         /* Force context change */
         isync
-#endif /* CONFIG_SERIAL_TEXT_DEBUG */
+#endif /* CONFIG_PPC_EARLY_DEBUG_44x */
 
         /* Establish the interrupt vector offsets */
         SET_IVOR(0,  CriticalInput);
diff --git a/arch/powerpc/kernel/of_platform.c b/arch/powerpc/kernel/of_platform.c
index 908ed7926db4..84c34d979a88 100644
--- a/arch/powerpc/kernel/of_platform.c
+++ b/arch/powerpc/kernel/of_platform.c
@@ -29,7 +29,6 @@
 #include <asm/ppc-pci.h>
 #include <asm/atomic.h>
 
-
 /*
  * The list of OF IDs below is used for matching bus types in the
  * system whose devices are to be exposed as of_platform_devices.
diff --git a/arch/powerpc/kernel/udbg.c b/arch/powerpc/kernel/udbg.c
index 7e0971868fc2..7ef97ea8b3ef 100644
--- a/arch/powerpc/kernel/udbg.c
+++ b/arch/powerpc/kernel/udbg.c
@@ -51,6 +51,9 @@ void __init udbg_early_init(void)
         udbg_init_pas_realmode();
 #elif defined(CONFIG_BOOTX_TEXT)
         udbg_init_btext();
+#elif defined(CONFIG_PPC_EARLY_DEBUG_44x)
+        /* PPC44x debug */
+        udbg_init_44x_as1();
 #endif
 }
 
diff --git a/arch/powerpc/kernel/udbg_16550.c b/arch/powerpc/kernel/udbg_16550.c
index a963f657222b..7afab5bcd61a 100644
--- a/arch/powerpc/kernel/udbg_16550.c
+++ b/arch/powerpc/kernel/udbg_16550.c
@@ -191,3 +191,26 @@ void udbg_init_pas_realmode(void)
         udbg_getc_poll = NULL;
 }
 #endif /* CONFIG_PPC_MAPLE */
+
+#ifdef CONFIG_PPC_EARLY_DEBUG_44x
+#include <platforms/44x/44x.h>
+
+static void udbg_44x_as1_putc(char c)
+{
+        if (udbg_comport) {
+                while ((as1_readb(&udbg_comport->lsr) & LSR_THRE) == 0)
+                        /* wait for idle */;
+                as1_writeb(c, &udbg_comport->thr); eieio();
+                if (c == '\n')
+                        udbg_44x_as1_putc('\r');
+        }
+}
+
+void __init udbg_init_44x_as1(void)
+{
+        udbg_comport =
+                (volatile struct NS16550 __iomem *)PPC44x_EARLY_DEBUG_VIRTADDR;
+
+        udbg_putc = udbg_44x_as1_putc;
+}
+#endif /* CONFIG_PPC_EARLY_DEBUG_44x */
diff --git a/arch/powerpc/platforms/44x/44x.h b/arch/powerpc/platforms/44x/44x.h
index 45f24b166f4d..42eabf87fea3 100644
--- a/arch/powerpc/platforms/44x/44x.h
+++ b/arch/powerpc/platforms/44x/44x.h
@@ -1,6 +1,8 @@
 #ifndef __POWERPC_PLATFORMS_44X_44X_H
 #define __POWERPC_PLATFORMS_44X_44X_H
 
+extern u8 as1_readb(volatile u8 __iomem  *addr);
+extern void as1_writeb(u8 data, volatile u8 __iomem *addr);
 extern void ppc44x_reset_system(char *cmd);
 
 #endif /* __POWERPC_PLATFORMS_44X_44X_H */
diff --git a/arch/powerpc/platforms/44x/misc_44x.S b/arch/powerpc/platforms/44x/misc_44x.S
index 52bde71485bd..3bce71d5d756 100644
--- a/arch/powerpc/platforms/44x/misc_44x.S
+++ b/arch/powerpc/platforms/44x/misc_44x.S
@@ -15,6 +15,37 @@
         .text
 
 /*
+ * Do an IO access in AS1
+ */
+_GLOBAL(as1_readb)
+        mfmsr   r7
+        ori     r0,r7,MSR_DS
+        sync
+        mtmsr   r0
+        sync
+        isync
+        lbz     r3,0(r3)
+        sync
+        mtmsr   r7
+        sync
+        isync
+        blr
+
+_GLOBAL(as1_writeb)
+        mfmsr   r7
+        ori     r0,r7,MSR_DS
+        sync
+        mtmsr   r0
+        sync
+        isync
+        stb     r3,0(r4)
+        sync
+        mtmsr   r7
+        sync
+        isync
+        blr
+
+/*
  * void ppc44x_reset_system(char *cmd)
  *
  * At present, this routine just applies a system reset.