Hi Nuno,
Thanks for reporting this and the patch.
On 11/01/18 13:38, Nuno Goncalves wrote:
> When target_rate is big enough and not permitted in hardware,
> then i is looped to UART_DIV_MAX (0xFFFF), and i * max_rate will overflow
> (32b signed).
>
> A fix is to quit the loop early enough, as soon as rate < i * min_rate as it
> means the rate is not permitted.
'rate < i * min_rate' does not mean the rate is not permitted. clk_round_rate() gives the nearest achievable rate to the one requested, which may be lower than i * min_rate. This is not an error and in this case we want to continue the loop searching for an acceptable rate.
>
> This avoids arbitraty rates to be applied. Still in my hardware the max
> allowed rate (1500000) is aplied when a higher is requested. This seems a
> artifact of clk_round_rate which is not understood by me and independent of
> this fix. Might or might not be another bug.
>
> Signed-off-by: Nuno Goncalves <nunojpg@xxxxxxxxx>
> ---
> drivers/tty/serial/8250/8250_dw.c | 8 +++++++-
> 1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c
> index 5bb0c42c88dd..a27ea916abbf 100644
> --- a/drivers/tty/serial/8250/8250_dw.c
> +++ b/drivers/tty/serial/8250/8250_dw.c
> @@ -267,7 +267,13 @@ static void dw8250_set_termios(struct uart_port *p, struct ktermios *termios,
>
> for (i = 1; i <= UART_DIV_MAX; i++) {
> rate = clk_round_rate(d->clk, i * target_rate);
> - if (rate >= i * min_rate && rate <= i * max_rate)
> +
> + if (rate < i * min_rate) {
> + i = UART_DIV_MAX + 1;
> + break;
> + }
> +
> + if (rate <= i * max_rate)
> break;
> }
> if (i <= UART_DIV_MAX) {
--
Ed
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