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>

1 files changed, 15 insertions, 1 deletions

diff --git a/arch/arm/mach-omap2/pm24xx.c b/arch/arm/mach-omap2/pm24xx.c
index d38f3121dde9..db1025562fb0 100644
--- a/arch/arm/mach-omap2/pm24xx.c
+++ b/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);