[POWERPC] 4xx: Add early udbg support for 40x processors

This adds some basic real mode based early udbg support for 40x
in order to debug things more easily

Signed-off-by: Benjamin Herrenschmidt <[e-mail]>
Signed-off-by: Josh Boyer <[e-mail]>

arch/powerpc/Kconfig.debug

···
 	  Select this to enable early debugging for IBM 44x chips via the
 	  inbuilt serial port.
 
+config PPC_EARLY_DEBUG_40x
+	bool "Early serial debugging for IBM/AMCC 40x CPUs"
+	depends on 40x
+	help
+	  Select this to enable early debugging for IBM 40x chips via the
+	  inbuilt serial port. This works on chips with a 16550 compatible
+	  UART. Xilinx chips with uartlite cannot use this option.
+
 config PPC_EARLY_DEBUG_CPM
 	bool "Early serial debugging for Freescale CPM-based serial ports"
 	depends on SERIAL_CPM
···
 	hex "EPRN of early debug UART physical address"
 	depends on PPC_EARLY_DEBUG_44x
 	default "0x1"
+
+config PPC_EARLY_DEBUG_40x_PHYSADDR
+	hex "Early debug UART physical address"
+	depends on PPC_EARLY_DEBUG_40x
+	default "0xef600300"
 
 config PPC_EARLY_DEBUG_CPM_ADDR
 	hex "CPM UART early debug transmit descriptor address"

arch/powerpc/kernel/misc_32.S

···
 	isync
 	blr			/* Done */
 
+#ifdef CONFIG_40x
+
+/*
+ * Do an IO access in real mode
+ */
+_GLOBAL(real_readb)
+	mfmsr	r7
+	ori	r0,r7,MSR_DR
+	xori	r0,r0,MSR_DR
+	sync
+	mtmsr	r0
+	sync
+	isync
+	lbz	r3,0(r3)
+	sync
+	mtmsr	r7
+	sync
+	isync
+	blr
+
+	/*
+ * Do an IO access in real mode
+ */
+_GLOBAL(real_writeb)
+	mfmsr	r7
+	ori	r0,r7,MSR_DR
+	xori	r0,r0,MSR_DR
+	sync
+	mtmsr	r0
+	sync
+	isync
+	stb	r3,0(r4)
+	sync
+	mtmsr	r7
+	sync
+	isync
+	blr
+
+#endif /* CONFIG_40x */
 
 /*
  * Flush MMU TLB

arch/powerpc/kernel/udbg.c

···
 #elif defined(CONFIG_PPC_EARLY_DEBUG_44x)
 	/* PPC44x debug */
 	udbg_init_44x_as1();
+#elif defined(CONFIG_PPC_EARLY_DEBUG_40x)
+	/* PPC40x debug */
+	udbg_init_40x_realmode();
 #elif defined(CONFIG_PPC_EARLY_DEBUG_CPM)
 	udbg_init_cpm();
 #endif

arch/powerpc/kernel/udbg_16550.c

···
 	udbg_getc = udbg_44x_as1_getc;
 }
 #endif /* CONFIG_PPC_EARLY_DEBUG_44x */
+
+#ifdef CONFIG_PPC_EARLY_DEBUG_40x
+static void udbg_40x_real_putc(char c)
+{
+	if (udbg_comport) {
+		while ((real_readb(&udbg_comport->lsr) & LSR_THRE) == 0)
+			/* wait for idle */;
+		real_writeb(c, &udbg_comport->thr); eieio();
+		if (c == '\n')
+			udbg_40x_real_putc('\r');
+	}
+}
+
+static int udbg_40x_real_getc(void)
+{
+	if (udbg_comport) {
+		while ((real_readb(&udbg_comport->lsr) & LSR_DR) == 0)
+			; /* wait for char */
+		return real_readb(&udbg_comport->rbr);
+	}
+	return -1;
+}
+
+void __init udbg_init_40x_realmode(void)
+{
+	udbg_comport = (struct NS16550 __iomem *)
+		CONFIG_PPC_EARLY_DEBUG_40x_PHYSADDR;
+
+	udbg_putc = udbg_40x_real_putc;
+	udbg_getc = udbg_40x_real_getc;
+	udbg_getc_poll = NULL;
+}
+#endif /* CONFIG_PPC_EARLY_DEBUG_40x */

arch/powerpc/platforms/Kconfig.cputype

···
 	bool "AMCC 40x"
 	select PPC_DCR_NATIVE
 	select WANT_DEVICE_TREE
+	select PPC_UDBG_16550
 
 config 44x
 	bool "AMCC 44x"

include/asm-powerpc/udbg.h

···
 extern void __init udbg_init_debug_beat(void);
 extern void __init udbg_init_btext(void);
 extern void __init udbg_init_44x_as1(void);
+extern void __init udbg_init_40x_realmode(void);
 extern void __init udbg_init_cpm(void);
 
 #endif /* __KERNEL__ */