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Date: Fri, 8 Jul 2022 00:47:37 +0530
From: Vijaya Krishna Nivarthi <quic_vnivarth@...cinc.com>
To: agross@...nel.org, bjorn.andersson@...aro.org,
konrad.dybcio@...ainline.org, gregkh@...uxfoundation.org,
jirislaby@...nel.org, linux-arm-msm@...r.kernel.org,
linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: quic_msavaliy@...cinc.com, dianders@...omium.org, mka@...omium.org,
swboyd@...omium.org,
Vijaya Krishna Nivarthi <quic_vnivarth@...cinc.com>
Subject: [V3] 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")
Signed-off-by: Vijaya Krishna Nivarthi <quic_vnivarth@...cinc.com>
---
v3: simplified algorithm further, fixed robot compile warnings
v2: removed minor optimisations to make more readable
v1: intial patch contained slightly complicated logic
---
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 2e23b65..ac2df1c 100644
--- a/drivers/tty/serial/qcom_geni_serial.c
+++ b/drivers/tty/serial/qcom_geni_serial.c
@@ -943,52 +943,71 @@ 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;
+ }
+
+ div = DIV_ROUND_UP(freq, desired_clk);
}
- if (!ser_clk) {
- pr_err("%s: Can't find matching DFS entry for baud %d\n",
- __func__, baud);
- return ser_clk;
+ 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) {
+ pr_err("%s: Invalid frequency\n", __func__);
+ return 0;
}
- *clk_div = ser_clk / desired_clk;
- if (!(*clk_div))
- *clk_div = 1;
+ /*
+ * try to find a clock rate within 2% tolerance, then within
+ */
+ 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);
+
+ if (!ser_clk)
+ pr_err("Couldn't find suitable clock rate for %lu\n", desired_clk);
+ else
+ pr_debug("desired_clk-%lu, ser_clk-%lu, clk_div-%lu\n",
+ desired_clk, ser_clk, *clk_div);
return ser_clk;
}
@@ -1021,8 +1040,7 @@ static void qcom_geni_serial_set_termios(struct uart_port *uport,
if (ver >= QUP_SE_VERSION_2_5)
sampling_rate /= 2;
- clk_rate = get_clk_div_rate(port->se.clk, baud,
- sampling_rate, &clk_div);
+ clk_rate = get_clk_div_rate(port->se.clk, baud, sampling_rate, &clk_div);
if (!clk_rate)
goto out_restart_rx;
--
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