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

Signed-off-by: Mike Frysinger <michael.frysinger@analog.com>
Signed-off-by: Bryan Wu <bryan.wu@analog.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 6 insertions, 3 deletions

diff --git a/arch/blackfin/mach-bf533/head.S b/arch/blackfin/mach-bf533/head.S
index 1a54ff5f061d..4db9e6240906 100644
--- a/arch/blackfin/mach-bf533/head.S
+++ b/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);
diff --git a/arch/blackfin/mach-bf537/head.S b/arch/blackfin/mach-bf537/head.S
index aafc686749ed..b4377dddc127 100644
--- a/arch/blackfin/mach-bf537/head.S
+++ b/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);
diff --git a/arch/blackfin/mach-bf561/head.S b/arch/blackfin/mach-bf561/head.S
index 04f3ac33ab0e..9c8e6885f4e7 100644
--- a/arch/blackfin/mach-bf561/head.S
+++ b/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);