uart: Fix bug in {uart8250, uart8250_mem, ns16550}_rx_byte functions

We have several different UART implementations of which three support a
timeout when receiving characters. In all of these three implementations
there is a bug where when the timeout is hit the last received character
will be returned instead of the needed 0.

The problem is that the timeout variable i is decremented after it has
been checked in the while-loop. That leads to the fact that when the
while-loop is aborted due to a timeout i will contain 0xffffffff and not
0. Thus in turn will fool the following if-statement leading to wrong
return value to the caller in this case. Therefore the caller will see a
received character event if there is none.

Change-Id: I23ff531a1e729e816764f1a071484c924dcb0f85
Signed-off-by: Werner Zeh <werner.zeh@siemens.com>
Reviewed-on: https://review.coreboot.org/19731
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
This commit is contained in:
Werner Zeh 2017-05-17 10:13:24 +02:00
parent e87564ffe7
commit 43314ffae5
3 changed files with 8 additions and 3 deletions

View File

@ -62,7 +62,8 @@ static int uart8250_can_rx_byte(unsigned base_port)
static unsigned char uart8250_rx_byte(unsigned base_port) static unsigned char uart8250_rx_byte(unsigned base_port)
{ {
unsigned long int i = SINGLE_CHAR_TIMEOUT; unsigned long int i = SINGLE_CHAR_TIMEOUT;
while (i-- && !uart8250_can_rx_byte(base_port)); while (i && !uart8250_can_rx_byte(base_port))
i--;
if (i) if (i)
return inb(base_port + UART8250_RBR); return inb(base_port + UART8250_RBR);

View File

@ -82,8 +82,10 @@ static int uart8250_mem_can_rx_byte(void *base)
static unsigned char uart8250_mem_rx_byte(void *base) static unsigned char uart8250_mem_rx_byte(void *base)
{ {
unsigned long int i = SINGLE_CHAR_TIMEOUT; unsigned long int i = SINGLE_CHAR_TIMEOUT;
while (i-- && !uart8250_mem_can_rx_byte(base)) while (i && !uart8250_mem_can_rx_byte(base)) {
udelay(1); udelay(1);
i--;
}
if (i) if (i)
return uart8250_read(base, UART8250_RBR); return uart8250_read(base, UART8250_RBR);
else else

View File

@ -84,8 +84,10 @@ static int ns16550_tst_byte(void)
static unsigned char ns16550_rx_byte(void) static unsigned char ns16550_rx_byte(void)
{ {
unsigned long int i = SINGLE_CHAR_TIMEOUT; unsigned long int i = SINGLE_CHAR_TIMEOUT;
while (i-- && !ns16550_tst_byte()) while (i && !ns16550_tst_byte()) {
udelay(1); udelay(1);
i--;
}
if (i) if (i)
return read32(&regs->rbr); return read32(&regs->rbr);
else else