From c2a3e84f950e7ddba1f3914b005861d46ae60359 Mon Sep 17 00:00:00 2001 From: Stephen Boyd Date: Tue, 25 Oct 2011 19:19:43 -0700 Subject: [PATCH] tty: hvc_dcc: Fix duplicate character inputs Reading from the DCC grabs a character from the buffer and clears the status bit. Since this is a context-changing operation, instructions following the character read that rely on the status bit being accurate need to be synchronized with an ISB. In this case, the status bit check needs to execute after the character read otherwise we run the risk of reading the character and checking the status bit before the read can clear the status bit in the first place. When this happens, the user will see the same character they typed twice, instead of once. Add an ISB after the read and the write, so that the status check is synchronized with the read/write operations. Signed-off-by: Stephen Boyd Cc: stable Signed-off-by: Greg Kroah-Hartman --- drivers/tty/hvc/hvc_dcc.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/drivers/tty/hvc/hvc_dcc.c b/drivers/tty/hvc/hvc_dcc.c index 435f6facbc23..44fbebab5075 100644 --- a/drivers/tty/hvc/hvc_dcc.c +++ b/drivers/tty/hvc/hvc_dcc.c @@ -46,6 +46,7 @@ static inline char __dcc_getchar(void) asm volatile("mrc p14, 0, %0, c0, c5, 0 @ read comms data reg" : "=r" (__c)); + isb(); return __c; } @@ -55,6 +56,7 @@ static inline void __dcc_putchar(char c) asm volatile("mcr p14, 0, %0, c0, c5, 0 @ write a char" : /* no output register */ : "r" (c)); + isb(); } static int hvc_dcc_put_chars(uint32_t vt, const char *buf, int count) -- 2.20.1