From c474c775716edd46a51bf8161142bbd1545f8733 Mon Sep 17 00:00:00 2001 From: Vijaya Krishna Nivarthi Date: Sat, 16 Jul 2022 00:25:43 +0530 Subject: [PATCH] tty: serial: qcom-geni-serial: Fix get_clk_div_rate() which otherwise could return a sub-optimal clock rate. In the logic around call to clk_round_rate(), for some corner conditions, get_clk_div_rate() could return an sub-optimal clock rate. Also, if an exact clock rate was not found lowest clock was being returned. Search for suitable clock rate in 2 steps a) exact match or within 2% tolerance b) within 5% tolerance This also takes care of corner conditions. Fixes: c2194bc999d4 ("tty: serial: qcom-geni-serial: Remove uart frequency table. Instead, find suitable frequency with call to clk_round_rate") Reviewed-by: Douglas Anderson Signed-off-by: Vijaya Krishna Nivarthi Link: https://lore.kernel.org/r/1657911343-1909-1-git-send-email-quic_vnivarth@quicinc.com Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/qcom_geni_serial.c | 88 +++++++++++++++++++++-------------- 1 file changed, 53 insertions(+), 35 deletions(-) diff --git a/drivers/tty/serial/qcom_geni_serial.c b/drivers/tty/serial/qcom_geni_serial.c index f8f9506..f754619 100644 --- a/drivers/tty/serial/qcom_geni_serial.c +++ b/drivers/tty/serial/qcom_geni_serial.c @@ -940,52 +940,63 @@ static int qcom_geni_serial_startup(struct uart_port *uport) return 0; } -static unsigned long get_clk_div_rate(struct clk *clk, unsigned int baud, - unsigned int sampling_rate, unsigned int *clk_div) +static unsigned long find_clk_rate_in_tol(struct clk *clk, unsigned int desired_clk, + unsigned int *clk_div, unsigned int percent_tol) { - unsigned long ser_clk; - unsigned long desired_clk; - unsigned long freq, prev; + unsigned long freq; unsigned long div, maxdiv; - int64_t mult; - - desired_clk = baud * sampling_rate; - if (!desired_clk) { - pr_err("%s: Invalid frequency\n", __func__); - return 0; - } + u64 mult; + unsigned long offset, abs_tol, achieved; + abs_tol = div_u64((u64)desired_clk * percent_tol, 100); maxdiv = CLK_DIV_MSK >> CLK_DIV_SHFT; - prev = 0; - - for (div = 1; div <= maxdiv; div++) { - mult = div * desired_clk; - if (mult > ULONG_MAX) + div = 1; + while (div <= maxdiv) { + mult = (u64)div * desired_clk; + if (mult != (unsigned long)mult) break; - freq = clk_round_rate(clk, (unsigned long)mult); - if (!(freq % desired_clk)) { - ser_clk = freq; - break; - } + offset = div * abs_tol; + freq = clk_round_rate(clk, mult - offset); - if (!prev) - ser_clk = freq; - else if (prev == freq) + /* Can only get lower if we're done */ + if (freq < mult - offset) break; - prev = freq; - } + /* + * Re-calculate div in case rounding skipped rates but we + * ended up at a good one, then check for a match. + */ + div = DIV_ROUND_CLOSEST(freq, desired_clk); + achieved = DIV_ROUND_CLOSEST(freq, div); + if (achieved <= desired_clk + abs_tol && + achieved >= desired_clk - abs_tol) { + *clk_div = div; + return freq; + } - if (!ser_clk) { - pr_err("%s: Can't find matching DFS entry for baud %d\n", - __func__, baud); - return ser_clk; + div = DIV_ROUND_UP(freq, desired_clk); } - *clk_div = ser_clk / desired_clk; - if (!(*clk_div)) - *clk_div = 1; + return 0; +} + +static unsigned long get_clk_div_rate(struct clk *clk, unsigned int baud, + unsigned int sampling_rate, unsigned int *clk_div) +{ + unsigned long ser_clk; + unsigned long desired_clk; + + desired_clk = baud * sampling_rate; + if (!desired_clk) + return 0; + + /* + * try to find a clock rate within 2% tolerance, then within 5% + */ + ser_clk = find_clk_rate_in_tol(clk, desired_clk, clk_div, 2); + if (!ser_clk) + ser_clk = find_clk_rate_in_tol(clk, desired_clk, clk_div, 5); return ser_clk; } @@ -1020,8 +1031,15 @@ static void qcom_geni_serial_set_termios(struct uart_port *uport, clk_rate = get_clk_div_rate(port->se.clk, baud, sampling_rate, &clk_div); - if (!clk_rate) + if (!clk_rate) { + dev_err(port->se.dev, + "Couldn't find suitable clock rate for %lu\n", + baud * sampling_rate); goto out_restart_rx; + } + + dev_dbg(port->se.dev, "desired_rate-%lu, clk_rate-%lu, clk_div-%u\n", + baud * sampling_rate, clk_rate, clk_div); uport->uartclk = clk_rate; dev_pm_opp_set_rate(uport->dev, clk_rate); -- 2.7.4