diff options
Diffstat (limited to 'drivers/tty')
| -rw-r--r-- | drivers/tty/serial/sh-sci.c | 51 |
1 files changed, 24 insertions, 27 deletions
diff --git a/drivers/tty/serial/sh-sci.c b/drivers/tty/serial/sh-sci.c index 306497ee5c32..c3a193616484 100644 --- a/drivers/tty/serial/sh-sci.c +++ b/drivers/tty/serial/sh-sci.c @@ -1872,13 +1872,24 @@ static void sci_baud_calc_hscif(struct sci_port *s, unsigned int bps, unsigned int *srr, unsigned int *cks) { unsigned int sr, br, prediv, scrate, c; - int err, recv_margin; - int min_err = INT_MAX; - int recv_max_margin = 0; + int err, min_err = INT_MAX; - /* Find the combination of sample rate and clock select with the - smallest deviation from the desired baud rate. */ - for (sr = 8; sr <= 32; sr++) { + /* + * Find the combination of sample rate and clock select with the + * smallest deviation from the desired baud rate. + * Prefer high sample rates to maximise the receive margin. + * + * M: Receive margin (%) + * N: Ratio of bit rate to clock (N = sampling rate) + * D: Clock duty (D = 0 to 1.0) + * L: Frame length (L = 9 to 12) + * F: Absolute value of clock frequency deviation + * + * M = |(0.5 - 1 / 2 * N) - ((L - 0.5) * F) - + * (|D - 0.5| / N * (1 + F))| + * NOTE: Usually, treat D for 0.5, F is 0 by this calculation. + */ + for (sr = 32; sr >= 8; sr--) { for (c = 0; c <= 3; c++) { /* integerized formulas from HSCIF documentation */ prediv = sr * (1 << (2 * c + 1)); @@ -1898,36 +1909,22 @@ static void sci_baud_calc_hscif(struct sci_port *s, unsigned int bps, scrate = prediv * bps; br = DIV_ROUND_CLOSEST(freq, scrate); br = clamp(br, 1U, 256U); + err = DIV_ROUND_CLOSEST(freq, br * prediv) - bps; - /* Calc recv margin - * M: Receive margin (%) - * N: Ratio of bit rate to clock (N = sampling rate) - * D: Clock duty (D = 0 to 1.0) - * L: Frame length (L = 9 to 12) - * F: Absolute value of clock frequency deviation - * - * M = |(0.5 - 1 / 2 * N) - ((L - 0.5) * F) - - * (|D - 0.5| / N * (1 + F))| - * NOTE: Usually, treat D for 0.5, F is 0 by this - * calculation. - */ - recv_margin = abs((500 - - DIV_ROUND_CLOSEST(1000, sr << 1)) / 10); - if (abs(min_err) > abs(err)) { - min_err = err; - recv_max_margin = recv_margin; - } else if ((min_err == err) && - (recv_margin > recv_max_margin)) - recv_max_margin = recv_margin; - else + if (abs(err) >= abs(min_err)) continue; + min_err = err; *brr = br - 1; *srr = sr - 1; *cks = c; + + if (!err) + goto found; } } +found: dev_dbg(s->port.dev, "BRR: %u%+d bps using N %u SR %u cks %u\n", bps, min_err, *brr, *srr + 1, *cks); } |