[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 86aa374..f70e795 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 a51026f0..8869596 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 908ed79..84c34d9 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 7e09718..7ef97ea 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 a963f65..7afab5b 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 45f24b1..42eabf8 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 52bde71..3bce71d 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.