mips: Add CPS_NS16550_WIDTH config

On some platforms IO-memory might require to use a proper load/store
instructions (like Baikal-T1 IO-memory). To fix the cps-vec UART debug
printout let's add the CONFIG_CPS_NS16550_WIDTH config to determine which
instructions lb/sb, lh/sh or lw/sw are required for MMIO operations.
Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Cc: Alexey Malahov <Alexey.Malahov@baikalelectronics.ru>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Paul Burton <paulburton@kernel.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: devicetree@vger.kernel.org
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

arch/mips/Kconfig.debug

@@ -148,4 +148,14 @@ config MIPS_CPS_NS16550_SHIFT
 	  form their addresses. That is, log base 2 of the span between
 	  adjacent ns16550 registers in the system.
 
+config MIPS_CPS_NS16550_WIDTH
+	int "UART Register Width"
+	default 1
+	help
+	  ns16550 registers width. UART registers IO access methods will be
+	  selected in accordance with this parameter. By setting it to 1, 2 or
+	  4 UART registers will be accessed by means of lb/sb, lh/sh or lw/sw
+	  instructions respectively. Any value not from that set activates
+	  lb/sb instructions.
+
 endif # MIPS_CPS_NS16550_BOOL

arch/mips/kernel/cps-vec-ns16550.S

@@ -14,16 +14,30 @@
 #define UART_TX_OFS	(UART_TX << CONFIG_MIPS_CPS_NS16550_SHIFT)
 #define UART_LSR_OFS	(UART_LSR << CONFIG_MIPS_CPS_NS16550_SHIFT)
 
+#if CONFIG_MIPS_CPS_NS16550_WIDTH == 1
+# define UART_L		lb
+# define UART_S		sb
+#elif CONFIG_MIPS_CPS_NS16550_WIDTH == 2
+# define UART_L		lh
+# define UART_S		sh
+#elif CONFIG_MIPS_CPS_NS16550_WIDTH == 4
+# define UART_L		lw
+# define UART_S		sw
+#else
+# define UART_L		lb
+# define UART_S		sb
+#endif
+
 /**
  * _mips_cps_putc() - write a character to the UART
  * @a0: ASCII character to write
  * @t9: UART base address
  */
 LEAF(_mips_cps_putc)
-1:	lw		t0, UART_LSR_OFS(t9)
+1:	UART_L		t0, UART_LSR_OFS(t9)
 	andi		t0, t0, UART_LSR_TEMT
 	beqz		t0, 1b
-	sb		a0, UART_TX_OFS(t9)
+	UART_S		a0, UART_TX_OFS(t9)
 	jr		ra
 	END(_mips_cps_putc)