[PATCH] serial: 8250: Add cpufreq support

[Chaithrika U S]

On DA850/OMAP-L138 SoC, the PLL which supplies the clock to CPU also feeds the
UART and the UART input frequency can change when the CPU frequency is scaled.

This patch adds cpufreq support for 8250 serial driver. A clk structure member
has been added to the platform and port data structures. This member is used by
the cpufreq notifier callback to get the updated clock rate. The implementation
is based on the cpufreq implementation for Samsung serial driver.

Tested on TI DA850/OMAP-L138 EVM.

Signed-off-by: Chaithrika U S <chaithrika@xxxxxx>
---
Applies to Linus' kernel tree.

 drivers/serial/8250.c       |   79 +++++++++++++++++++++++++++++++++++++++++++
 include/linux/serial_8250.h |    1 +
 2 files changed, 80 insertions(+), 0 deletions(-)

diff --git a/drivers/serial/8250.c b/drivers/serial/8250.c
index c3e37c8..a64d1de 100644
--- a/drivers/serial/8250.c
+++ b/drivers/serial/8250.c
@@ -38,6 +38,8 @@
 #include <linux/serial_8250.h>
 #include <linux/nmi.h>
 #include <linux/mutex.h>
+#include <linux/cpufreq.h>
+#include <linux/clk.h>
 
 #include <asm/io.h>
 #include <asm/irq.h>
@@ -156,6 +158,10 @@ struct uart_8250_port {
 	 */
 	void			(*pm)(struct uart_port *port,
 				      unsigned int state, unsigned int old);
+	struct clk		*clk;
+#ifdef CONFIG_CPU_FREQ
+	struct notifier_block	freq_transition;
+#endif
 };
 
 struct irq_info {
@@ -2931,6 +2937,70 @@ void serial8250_resume_port(int line)
 	uart_resume_port(&serial8250_reg, &up->port);
 }
 
+#ifdef CONFIG_CPU_FREQ
+static int serial8250_cpufreq_transition(struct notifier_block *nb,
+					     unsigned long val, void *data)
+{
+	struct uart_8250_port *p;
+	struct uart_port *uport;
+
+	p = container_of(nb, struct uart_8250_port, freq_transition);
+	uport = &p->port;
+
+	if (IS_ERR(p->clk))
+		goto cpu_freq_exit;
+
+	if (p->port.uartclk == clk_get_rate(p->clk))
+		goto cpu_freq_exit;
+
+	p->port.uartclk = clk_get_rate(p->clk);
+	if (val == CPUFREQ_POSTCHANGE) {
+		struct ktermios *termios;
+		struct tty_struct *tty;
+		if (uport->state == NULL)
+			goto cpu_freq_exit;
+
+		tty = uport->state->port.tty;
+		if (tty == NULL)
+			goto cpu_freq_exit;
+
+		termios = tty->termios;
+		if (termios == NULL) {
+			printk(KERN_WARNING "%s: no termios?\n", __func__);
+			goto cpu_freq_exit;
+		}
+
+		serial8250_set_termios(uport, termios, NULL);
+	}
+
+cpu_freq_exit:
+	return 0;
+}
+
+static inline int serial8250_cpufreq_register(struct uart_8250_port *p)
+{
+	p->freq_transition.notifier_call = serial8250_cpufreq_transition;
+
+	return cpufreq_register_notifier(&p->freq_transition,
+					 CPUFREQ_TRANSITION_NOTIFIER);
+}
+
+static inline void serial8250_cpufreq_deregister(struct uart_8250_port *p)
+{
+	cpufreq_unregister_notifier(&p->freq_transition,
+				    CPUFREQ_TRANSITION_NOTIFIER);
+}
+#else
+static inline int serial8250_cpufreq_register(struct uart_8250_port *p)
+{
+	return 0;
+}
+
+static inline void serial8250_cpufreq_deregister(struct uart_8250_port *p)
+{
+}
+#endif
+
 /*
  * Register a set of serial devices attached to a platform device.  The
  * list is terminated with a zero flags entry, which means we expect
@@ -2964,6 +3034,9 @@ static int __devinit serial8250_probe(struct platform_device *dev)
 		port.serial_out		= p->serial_out;
 		port.dev		= &dev->dev;
 		port.irqflags		|= irqflag;
+		if (p->clk)
+			serial8250_ports[i].clk = p->clk;
+
 		ret = serial8250_register_port(&port);
 		if (ret < 0) {
 			dev_err(&dev->dev, "unable to register port at index %d "
@@ -3133,6 +3206,11 @@ int serial8250_register_port(struct uart_port *port)
 		ret = uart_add_one_port(&serial8250_reg, &uart->port);
 		if (ret == 0)
 			ret = uart->port.line;
+
+		ret = serial8250_cpufreq_register(uart);
+		if (ret < 0)
+			printk(KERN_ERR "Failed to add cpufreq notifier\n");
+
 	}
 	mutex_unlock(&serial_mutex);
 
@@ -3152,6 +3230,7 @@ void serial8250_unregister_port(int line)
 	struct uart_8250_port *uart = &serial8250_ports[line];
 
 	mutex_lock(&serial_mutex);
+	serial8250_cpufreq_deregister(uart);
 	uart_remove_one_port(&serial8250_reg, &uart->port);
 	if (serial8250_isa_devs) {
 		uart->port.flags &= ~UPF_BOOT_AUTOCONF;
diff --git a/include/linux/serial_8250.h b/include/linux/serial_8250.h
index fb46aba..57d6e69 100644
--- a/include/linux/serial_8250.h
+++ b/include/linux/serial_8250.h
@@ -23,6 +23,7 @@ struct plat_serial8250_port {
 	resource_size_t	mapbase;	/* resource base */
 	unsigned int	irq;		/* interrupt number */
 	unsigned long	irqflags;	/* request_irq flags */
+	struct clk	*clk;
 	unsigned int	uartclk;	/* UART clock rate */
 	void            *private_data;
 	unsigned char	regshift;	/* register shift */
-- 
1.5.6

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