aboutsummaryrefslogtreecommitdiffstats
path: root/target/linux/ar71xx/patches-3.7/004-tty-serial-ar933x_uart-fix-baud-rate-calculation.patch
blob: 44eebabb180da311b5a0d126305a2054c3ccd0d3 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
From 2dff8ad92661b6c99e9ba8b5918e43b522551556 Mon Sep 17 00:00:00 2001
From: Gabor Juhos <juhosg@openwrt.org>
Date: Wed, 14 Nov 2012 10:38:13 +0100
Subject: [PATCH] tty/serial/ar933x_uart: fix baud rate calculation

commit 2dff8ad92661b6c99e9ba8b5918e43b522551556 upstream.

The UART of the AR933x SoC implements a fractional divisor
for generating the desired baud rate.

The current code uses a fixed value for the fractional
part of the divisor, and this leads to improperly
calculated baud rates:

   baud    scale   step  real baud         diff
     300   5207*   8192     17756     17456   5818.66%
     600   2603*   8192     35511     34911   5818.50%
    1200   1301*   8192     71023     69823   5818.58%
    2400    650*   8192     11241      8841    368.37%
    4800    324*   8192     22645     17845    371.77%
    9600    161    8192      9645        45      0.46%
   14400    107    8192     14468        68      0.47%
   19200     80    8192     19290        90      0.46%
   28800     53    8192     28935       135      0.46%
   38400     39    8192     39063       663      1.72%
   57600     26    8192     57870       270      0.46%
  115200     12    8192    120192      4992      4.33%
  230400      5    8192    260417     30017     13.02%
  460800      2    8192    520833     60033     13.02%
  921600      0    8192   1562500    640900     69.93%

After the patch, the integer and fractional parts of the
divisor will be calculated dynamically. This ensures that
the UART will use correct baud rates:

   baud    scale   step  real baud         diff
     300      6      11       300         0      0.00%
     600     54     173       600         0      0.00%
    1200     30     195      1200         0      0.00%
    2400     30     390      2400         0      0.00%
    4800     48    1233      4800         0      0.00%
    9600     78    3976      9600         0      0.00%
   14400     98    7474     14400         0      0.00%
   19200     55    5637     19200         0      0.00%
   28800    130   19780     28800         0      0.00%
   38400     36    7449     38400         0      0.00%
   57600     78   23857     57600         0      0.00%
  115200     43   26575    115200         0      0.00%
  230400     23   28991    230400         0      0.00%
  460800     11   28991    460800         0      0.00%
  921600      5   28991    921599        -1      0.00%

Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/tty/serial/ar933x_uart.c |   90 +++++++++++++++++++++++++++++++++++---
 1 file changed, 85 insertions(+), 5 deletions(-)

--- a/drivers/tty/serial/ar933x_uart.c
+++ b/drivers/tty/serial/ar933x_uart.c
@@ -25,11 +25,19 @@
 #include <linux/io.h>
 #include <linux/irq.h>
 
+#include <asm/div64.h>
+
 #include <asm/mach-ath79/ar933x_uart.h>
 #include <asm/mach-ath79/ar933x_uart_platform.h>
 
 #define DRIVER_NAME "ar933x-uart"
 
+#define AR933X_UART_MAX_SCALE	0xff
+#define AR933X_UART_MAX_STEP	0xffff
+
+#define AR933X_UART_MIN_BAUD	300
+#define AR933X_UART_MAX_BAUD	3000000
+
 #define AR933X_DUMMY_STATUS_RD	0x01
 
 static struct uart_driver ar933x_uart_driver;
@@ -37,6 +45,8 @@ static struct uart_driver ar933x_uart_dr
 struct ar933x_uart_port {
 	struct uart_port	port;
 	unsigned int		ier;	/* shadow Interrupt Enable Register */
+	unsigned int		min_baud;
+	unsigned int		max_baud;
 };
 
 static inline unsigned int ar933x_uart_read(struct ar933x_uart_port *up,
@@ -162,6 +172,57 @@ static void ar933x_uart_enable_ms(struct
 {
 }
 
+/*
+ * baudrate = (clk / (scale + 1)) * (step * (1 / 2^17))
+ */
+static unsigned long ar933x_uart_get_baud(unsigned int clk,
+					  unsigned int scale,
+					  unsigned int step)
+{
+	u64 t;
+	u32 div;
+
+	div = (2 << 16) * (scale + 1);
+	t = clk;
+	t *= step;
+	t += (div / 2);
+	do_div(t, div);
+
+	return t;
+}
+
+static void ar933x_uart_get_scale_step(unsigned int clk,
+				       unsigned int baud,
+				       unsigned int *scale,
+				       unsigned int *step)
+{
+	unsigned int tscale;
+	long min_diff;
+
+	*scale = 0;
+	*step = 0;
+
+	min_diff = baud;
+	for (tscale = 0; tscale < AR933X_UART_MAX_SCALE; tscale++) {
+		u64 tstep;
+		int diff;
+
+		tstep = baud * (tscale + 1);
+		tstep *= (2 << 16);
+		do_div(tstep, clk);
+
+		if (tstep > AR933X_UART_MAX_STEP)
+			break;
+
+		diff = abs(ar933x_uart_get_baud(clk, tscale, tstep) - baud);
+		if (diff < min_diff) {
+			min_diff = diff;
+			*scale = tscale;
+			*step = tstep;
+		}
+	}
+}
+
 static void ar933x_uart_set_termios(struct uart_port *port,
 				    struct ktermios *new,
 				    struct ktermios *old)
@@ -169,7 +230,7 @@ static void ar933x_uart_set_termios(stru
 	struct ar933x_uart_port *up = (struct ar933x_uart_port *) port;
 	unsigned int cs;
 	unsigned long flags;
-	unsigned int baud, scale;
+	unsigned int baud, scale, step;
 
 	/* Only CS8 is supported */
 	new->c_cflag &= ~CSIZE;
@@ -191,8 +252,8 @@ static void ar933x_uart_set_termios(stru
 	/* Mark/space parity is not supported */
 	new->c_cflag &= ~CMSPAR;
 
-	baud = uart_get_baud_rate(port, new, old, 0, port->uartclk / 16);
-	scale = (port->uartclk / (16 * baud)) - 1;
+	baud = uart_get_baud_rate(port, new, old, up->min_baud, up->max_baud);
+	ar933x_uart_get_scale_step(port->uartclk, baud, &scale, &step);
 
 	/*
 	 * Ok, we're now changing the port state. Do it with
@@ -200,6 +261,10 @@ static void ar933x_uart_set_termios(stru
 	 */
 	spin_lock_irqsave(&up->port.lock, flags);
 
+	/* disable the UART */
+	ar933x_uart_rmw_clear(up, AR933X_UART_CS_REG,
+		      AR933X_UART_CS_IF_MODE_M << AR933X_UART_CS_IF_MODE_S);
+
 	/* Update the per-port timeout. */
 	uart_update_timeout(port, new->c_cflag, baud);
 
@@ -210,7 +275,7 @@ static void ar933x_uart_set_termios(stru
 		up->port.ignore_status_mask |= AR933X_DUMMY_STATUS_RD;
 
 	ar933x_uart_write(up, AR933X_UART_CLOCK_REG,
-			  scale << AR933X_UART_CLOCK_SCALE_S | 8192);
+			  scale << AR933X_UART_CLOCK_SCALE_S | step);
 
 	/* setup configuration register */
 	ar933x_uart_rmw(up, AR933X_UART_CS_REG, AR933X_UART_CS_PARITY_M, cs);
@@ -219,6 +284,11 @@ static void ar933x_uart_set_termios(stru
 	ar933x_uart_rmw_set(up, AR933X_UART_CS_REG,
 			    AR933X_UART_CS_HOST_INT_EN);
 
+	/* reenable the UART */
+	ar933x_uart_rmw(up, AR933X_UART_CS_REG,
+			AR933X_UART_CS_IF_MODE_M << AR933X_UART_CS_IF_MODE_S,
+			AR933X_UART_CS_IF_MODE_DCE << AR933X_UART_CS_IF_MODE_S);
+
 	spin_unlock_irqrestore(&up->port.lock, flags);
 
 	if (tty_termios_baud_rate(new))
@@ -401,6 +471,8 @@ static void ar933x_uart_config_port(stru
 static int ar933x_uart_verify_port(struct uart_port *port,
 				   struct serial_struct *ser)
 {
+	struct ar933x_uart_port *up = (struct ar933x_uart_port *) port;
+
 	if (ser->type != PORT_UNKNOWN &&
 	    ser->type != PORT_AR933X)
 		return -EINVAL;
@@ -408,7 +480,8 @@ static int ar933x_uart_verify_port(struc
 	if (ser->irq < 0 || ser->irq >= NR_IRQS)
 		return -EINVAL;
 
-	if (ser->baud_base < 28800)
+	if (ser->baud_base < up->min_baud ||
+	    ser->baud_base > up->max_baud)
 		return -EINVAL;
 
 	return 0;
@@ -561,6 +634,7 @@ static int __devinit ar933x_uart_probe(s
 	struct uart_port *port;
 	struct resource *mem_res;
 	struct resource *irq_res;
+	unsigned int baud;
 	int id;
 	int ret;
 
@@ -611,6 +685,12 @@ static int __devinit ar933x_uart_probe(s
 	port->fifosize = AR933X_UART_FIFO_SIZE;
 	port->ops = &ar933x_uart_ops;
 
+	baud = ar933x_uart_get_baud(port->uartclk, AR933X_UART_MAX_SCALE, 1);
+	up->min_baud = max_t(unsigned int, baud, AR933X_UART_MIN_BAUD);
+
+	baud = ar933x_uart_get_baud(port->uartclk, 0, AR933X_UART_MAX_STEP);
+	up->max_baud = min_t(unsigned int, baud, AR933X_UART_MAX_BAUD);
+
 	ar933x_uart_add_console_port(up);
 
 	ret = uart_add_one_port(&ar933x_uart_driver, &up->port);