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SubjectRe: [PATCH] serial: sh-sci: Fix HSCIF RX sampling point calculation
Hi Geert,

On Mon, Apr 01, 2019 at 01:25:10PM +0200, Geert Uytterhoeven wrote:
> There are several issues with the formula used for calculating the
> deviation from the intended rate:
> 1. While min_err and last_stop are signed, srr and baud are unsigned.
> Hence the signed values are promoted to unsigned, which will lead
> to a bogus value of deviation if min_err is negative,
> 2. Srr is the register field value, which is one less than the actual
> sampling rate factor,
> 3. The divisions do not use rounding.
>
> Fix this by casting unsigned variables to int, adding one to srr, and
> using a single DIV_ROUND_CLOSEST().
>
> Fixes: 63ba1e00f178a448 ("serial: sh-sci: Support for HSCIF RX sampling point adjustment")
> Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
> ---
> Anyone with a good test setup for verifying this feature actually works
> as advertised?
> ---
> drivers/tty/serial/sh-sci.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/tty/serial/sh-sci.c b/drivers/tty/serial/sh-sci.c
> index 2bdaeba5d527a6ce..8dea59edde34c224 100644
> --- a/drivers/tty/serial/sh-sci.c
> +++ b/drivers/tty/serial/sh-sci.c
> @@ -2522,7 +2522,9 @@ static void sci_set_termios(struct uart_port *port, struct ktermios *termios,
> * center of the last stop bit in sampling clocks.
> */
> int last_stop = bits * 2 - 1;
> - int deviation = min_err * srr * last_stop / 2 / baud;
> + int deviation = DIV_ROUND_CLOSEST(min_err * last_stop *
> + (int)(srr + 1),
> + 2 * (int)baud);
>
> if (abs(deviation) >= 2) {
> /* At least two sampling clocks off at the

Just wanted to say thank you for your tremendous commitment and
continuity in supporting the R-Car platform (and beyond that), which
allowed us to gracefully overcome the problems encountered in the
project in the best possible time, specifically thanks to this patch.

Best regards,
Eugeniu.

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