OMAP3: PM: UART: disable clocks when idle and off-mode support

This patch allows the UART clocks to be disabled when the OMAP UARTs
are inactive, thus permitting the chip to hit retention in idle.
After the expiration of an activity timer, each UART is allowed to
disable its clocks so the system can enter retention.  The activity
timer is (re)activated on any UART interrupt, UART wake event or any
IO pad wakeup.  The actual disable of the UART clocks is done in the
'prepare_idle' hook called from the OMAP idle loop.

While the activity timer is active, the smart-idle mode of the UART is
also disabled.  This is due to a "feature" of the UART module that
after a UART wakeup, the smart-idle mode may be entered before the
UART has communicated the interrupt, or upon TX, an idle mode may be
entered before the TX FIFOs are emptied.

Upon suspend, the 'prepare_suspend' hook cancels any pending activity
timers and allows the clocks to be disabled immediately.

In addition, upon disabling clocks the UART state is saved in case
of an off-mode transition while clocks are off.

Special thanks to Tero Kristo for the initial ideas and first versions
of UART idle support, and to Jouni Hogander for extra testing and
bugfixes.

Tested on OMAP3 (Beagle, RX51, SDP, EVM) and OMAP2 (n810)

Cc: Tero Kristo <tero.kristo@nokia.com>
Cc: Jouni Hogander <jouni.hogander@nokia.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>

arch/arm/mach-omap2/pm24xx.c

@@ -71,6 +71,11 @@ static int omap2_fclks_active(void)
 
 	f1 = cm_read_mod_reg(CORE_MOD, CM_FCLKEN1);
 	f2 = cm_read_mod_reg(CORE_MOD, OMAP24XX_CM_FCLKEN2);
+
+	/* Ignore UART clocks.  These are handled by UART core (serial.c) */
+	f1 &= ~(OMAP24XX_EN_UART1 | OMAP24XX_EN_UART2);
+	f2 &= ~OMAP24XX_EN_UART3;
+
 	if (f1 | f2)
 		return 1;
 	return 0;
@@ -117,12 +122,20 @@ static void omap2_enter_full_retention(void)
 	if (omap_irq_pending())
 		goto no_sleep;
 
+	omap_uart_prepare_idle(0);
+	omap_uart_prepare_idle(1);
+	omap_uart_prepare_idle(2);
+
 	/* Jump to SRAM suspend code */
 	omap2_sram_suspend(sdrc_read_reg(SDRC_DLLA_CTRL),
 			   OMAP_SDRC_REGADDR(SDRC_DLLA_CTRL),
 			   OMAP_SDRC_REGADDR(SDRC_POWER));
-no_sleep:
 
+	omap_uart_resume_idle(2);
+	omap_uart_resume_idle(1);
+	omap_uart_resume_idle(0);
+
+no_sleep:
 	if (omap2_pm_debug) {
 		unsigned long long tmp;
 
@@ -283,6 +296,7 @@ static int omap2_pm_suspend(void)
 	mir1 = omap_readl(0x480fe0a4);
 	omap_writel(1 << 5, 0x480fe0ac);
 
+	omap_uart_prepare_suspend();
 	omap2_enter_full_retention();
 
 	omap_writel(mir1, 0x480fe0a4);

arch/arm/mach-omap2/pm34xx.c

@@ -27,6 +27,7 @@
 #include <mach/clockdomain.h>
 #include <mach/powerdomain.h>
 #include <mach/control.h>
+#include <mach/serial.h>
 
 #include "cm.h"
 #include "cm-regbits-34xx.h"
@@ -168,10 +169,16 @@ static void omap_sram_idle(void)
 		return;
 	}
 	omap2_gpio_prepare_for_retention();
+	omap_uart_prepare_idle(0);
+	omap_uart_prepare_idle(1);
+	omap_uart_prepare_idle(2);
 
 	_omap_sram_idle(NULL, save_state);
 	cpu_init();
 
+	omap_uart_resume_idle(2);
+	omap_uart_resume_idle(1);
+	omap_uart_resume_idle(0);
 	omap2_gpio_resume_after_retention();
 }
 
@@ -204,6 +211,11 @@ static int omap3_fclks_active(void)
 				  CM_FCLKEN);
 	fck_per = cm_read_mod_reg(OMAP3430_PER_MOD,
 				  CM_FCLKEN);
+
+	/* Ignore UART clocks.  These are handled by UART core (serial.c) */
+	fck_core1 &= ~(OMAP3430_EN_UART1 | OMAP3430_EN_UART2);
+	fck_per &= ~OMAP3430_EN_UART3;
+
 	if (fck_core1 | fck_core3 | fck_sgx | fck_dss |
 	    fck_cam | fck_per | fck_usbhost)
 		return 1;
@@ -212,6 +224,8 @@ static int omap3_fclks_active(void)
 
 static int omap3_can_sleep(void)
 {
+	if (!omap_uart_can_sleep())
+		return 0;
 	if (omap3_fclks_active())
 		return 0;
 	return 1;
@@ -301,6 +315,7 @@ static int omap3_pm_suspend(void)
 			goto restore;
 	}
 
+	omap_uart_prepare_suspend();
 	omap_sram_idle();
 
 restore:

arch/arm/plat-omap/include/mach/common.h

@@ -33,8 +33,6 @@ struct sys_timer;
 
 extern void omap_map_common_io(void);
 extern struct sys_timer omap_timer;
-extern void omap_serial_init(void);
-extern void omap_serial_enable_clocks(int enable);
 #if defined(CONFIG_I2C_OMAP) || defined(CONFIG_I2C_OMAP_MODULE)
 extern int omap_register_i2c_bus(int bus_id, u32 clkrate,
 				 struct i2c_board_info const *info,

arch/arm/plat-omap/include/mach/serial.h

@@ -40,4 +40,13 @@
 			__ret;						\
 			})
 
+#ifndef __ASSEMBLER__
+extern void omap_serial_init(void);
+extern int omap_uart_can_sleep(void);
+extern void omap_uart_check_wakeup(void);
+extern void omap_uart_prepare_suspend(void);
+extern void omap_uart_prepare_idle(int num);
+extern void omap_uart_resume_idle(int num);
+#endif
+
 #endif