From: "Maciej W. Rozycki" Polled transmission is tricky enough with the DZ11 design. While "loop" is set to a high value, conceptually you are not allowed to transmit without checking whether the device offers the right transmission line (yes, it is the device that selects the line -- the driver has no control over it other than disabling the transmitter offered if it is the wrong one), so the loop has to be run at least once. Well, the '1977 or PDP11 view of how serial lines should be handled... Except that the serial interface used to be quite an impressive board back then rather than chip. Signed-off-by: Maciej W. Rozycki Cc: Jiri Slaby Signed-off-by: Andrew Morton --- drivers/serial/dz.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff -puN drivers/serial/dz.c~dz-always-check-if-it-is-safe-to-console_putchar drivers/serial/dz.c --- a/drivers/serial/dz.c~dz-always-check-if-it-is-safe-to-console_putchar +++ a/drivers/serial/dz.c @@ -685,7 +685,7 @@ static void dz_console_putchar(struct ua iob(); spin_unlock_irqrestore(&dport->port.lock, flags); - while (loops--) { + do { trdy = dz_in(dport, DZ_CSR); if (!(trdy & DZ_TRDY)) continue; @@ -696,7 +696,7 @@ static void dz_console_putchar(struct ua dz_out(dport, DZ_TCR, mask); iob(); udelay(2); - } + } while (loops--); if (loops) /* Cannot send otherwise. */ dz_out(dport, DZ_TDR, ch); _