Blackfin arch: document why we have to touch the UART peripheral in our boot up code

Signed-off-by: NMike Frysinger <michael.frysinger@analog.com>
Signed-off-by: NBryan Wu <bryan.wu@analog.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

arch/blackfin/mach-bf533/head.S

@@ -173,7 +173,8 @@ ENTRY(__stext)
 	STI R2;
 #endif
 
-	/* Initialise UART */
+	/* Initialise UART - when booting from u-boot, the UART is not disabled
+	 * so if we dont initalize here, our serial console gets hosed */
 	p0.h = hi(UART_LCR);
 	p0.l = lo(UART_LCR);
 	r0 = 0x0(Z);

arch/blackfin/mach-bf537/head.S

@@ -181,7 +181,8 @@ ENTRY(__stext)
 	SSYNC;
 #endif
 
-	/*Initialise UART*/
+	/* Initialise UART - when booting from u-boot, the UART is not disabled
+	 * so if we dont initalize here, our serial console gets hosed */
 	p0.h = hi(UART_LCR);
 	p0.l = lo(UART_LCR);
 	r0 = 0x0(Z);

arch/blackfin/mach-bf561/head.S

@@ -127,7 +127,8 @@ ENTRY(__stext)
 	STI R2;
 #endif
 
-	/* Initialise UART*/
+	/* Initialise UART - when booting from u-boot, the UART is not disabled
+	 * so if we dont initalize here, our serial console gets hosed */
 	p0.h = hi(UART_LCR);
 	p0.l = lo(UART_LCR);
 	r0 = 0x0(Z);