linux-kernel - [V2] tty: serial: qcom-geni-serial: Remove uart frequency table. Instead, find suitable frequency with call to clk_round

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Message-Id: <1652697510-30543-1-git-send-email-quic_vnivarth@quicinc.com>
Date:   Mon, 16 May 2022 16:08:30 +0530
From:   Vijaya Krishna Nivarthi <quic_vnivarth@...cinc.com>
To:     agross@...nel.org, bjorn.andersson@...aro.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, quic_c_skakit@...cinc.com,
        Vijaya Krishna Nivarthi <quic_vnivarth@...cinc.com>
Subject: [V2] tty: serial: qcom-geni-serial: Remove uart frequency table. Instead, find suitable frequency with call to clk_round_rate.

Replace the UART frequency table 'root_freq[]' with logic around
clk_round_rate() so that SoC details like the available clk frequencies
can change and this driver still works. This reduces tight coupling
between this UART driver and the SoC clk driver because we no longer
have to update the 'root_freq[]' array for new SoCs. Instead the driver
determines the available frequencies at runtime.

Signed-off-by: Vijaya Krishna Nivarthi <quic_vnivarth@...cinc.com>
---
v2: loops through clk dividers to zero-in quickly
v1: intial patch looped through available clk frequencies
---
 drivers/tty/serial/qcom_geni_serial.c | 56 ++++++++++++++++++++++-------------
 1 file changed, 36 insertions(+), 20 deletions(-)

diff --git a/drivers/tty/serial/qcom_geni_serial.c b/drivers/tty/serial/qcom_geni_serial.c
index f496102..4733a23 100644
--- a/drivers/tty/serial/qcom_geni_serial.c
+++ b/drivers/tty/serial/qcom_geni_serial.c
@@ -149,12 +149,6 @@ static unsigned int qcom_geni_serial_tx_empty(struct uart_port *port);
 static void qcom_geni_serial_stop_rx(struct uart_port *uport);
 static void qcom_geni_serial_handle_rx(struct uart_port *uport, bool drop);
 
-static const unsigned long root_freq[] = {7372800, 14745600, 19200000, 29491200,
-					32000000, 48000000, 51200000, 64000000,
-					80000000, 96000000, 100000000,
-					102400000, 112000000, 120000000,
-					128000000};
-
 #define to_dev_port(ptr, member) \
 		container_of(ptr, struct qcom_geni_serial_port, member)
 
@@ -946,25 +940,43 @@ static int qcom_geni_serial_startup(struct uart_port *uport)
 	return 0;
 }
 
-static unsigned long get_clk_cfg(unsigned long clk_freq)
-{
-	int i;
-
-	for (i = 0; i < ARRAY_SIZE(root_freq); i++) {
-		if (!(root_freq[i] % clk_freq))
-			return root_freq[i];
-	}
-	return 0;
-}
-
-static unsigned long get_clk_div_rate(unsigned int baud,
+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;
+	unsigned long freq, prev;
+	unsigned long div, maxdiv;
+	int64_t mult;
 
 	desired_clk = baud * sampling_rate;
-	ser_clk = get_clk_cfg(desired_clk);
+	if (!desired_clk) {
+		pr_err("%s: Invalid frequency\n", __func__);
+		return 0;
+	}
+
+	maxdiv = CLK_DIV_MSK >> CLK_DIV_SHFT;
+	prev = 0;
+
+	for (div = 1; div <= maxdiv; div++) {
+		mult = div * desired_clk;
+		if (mult > ULONG_MAX)
+			break;
+
+		freq = clk_round_rate(clk, (unsigned long)mult);
+		if (!(freq % desired_clk)) {
+			ser_clk = freq;
+			break;
+		}
+
+		if (!prev)
+			ser_clk = freq;
+		else if (prev == freq)
+			break;
+
+		prev = freq;
+	}
+
 	if (!ser_clk) {
 		pr_err("%s: Can't find matching DFS entry for baud %d\n",
 								__func__, baud);
@@ -972,6 +984,9 @@ static unsigned long get_clk_div_rate(unsigned int baud,
 	}
 
 	*clk_div = ser_clk / desired_clk;
+	if (!(*clk_div))
+		*clk_div = 1;
+
 	return ser_clk;
 }
 
@@ -1003,7 +1018,8 @@ 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(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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