cc Tero, Govindraj
On Thu, 12 Jan 2012, NeilBrown wrote:
> On Wed, 11 Jan 2012 06:43:04 -0700 (MST) Paul Walmsley <paul@xxxxxxxxx> wrote:
>
> I spent some time exploring why cpuidle never drops below state 0 and found
> out that the code explicitly disables other states when uart is active - for
> a fairly broad definition of 'active'.
>
> I found the "sleep_timeout" setting and set them all to 1 second. This meant
> that cpuidle started working, but I got a lot of garbage characters.
>
...
> Does this really mean CPU_IDLE cannot be used when you might expect chars
> from a serial port - e.g. GPS or Bluetooth?
Hmmm. Looking at mach-omap2/pm34xx.c and mach-omap2/cpuidle34xx.c, it
indeed prevents even the MPU from entering a low-power state when the UART
is active, as you write. That doesn't seem correct.
Please try the following patch. It works fine for me on v3.2 with
omap2plus_defconfig on a 35xx BeagleBoard. No dropped or garbled
characters with console use. Not too surprising, since the UART has a
receive FIFO to withstand interrupt servicing delays.
- Paul
From: Paul Walmsley <paul@xxxxxxxxx>
Date: Fri, 13 Jan 2012 02:10:30 -0700
Subject: [PATCH] ARM: OMAP3: PM: allow MPU to enter low-power states even
when the UART is active
For some reason, both the existing OMAP3 PM code and the OMAP3 CPUIdle
driver prevent the MPU powerdomain from entering low-power modes when
any UART isn't asleep. Possibly it is intended to minimize the ARM
wakeup latency when UART activity arrives, but the UART has a FIFO
that should handle this for most cases, with no dropped characters. I
may be forgetting something important, though. And CORE/PER low-power
states are a different matter entirely.
Thanks to NeilBrown <neilb@xxxxxxx> for reporting the problem.
Signed-off-by: Paul Walmsley <paul@xxxxxxxxx>
Cc: NeilBrown <neilb@xxxxxxx>
Cc: Joe Woodward <jw@xxxxxxxxxxxxxx>
Cc: Tero Kristo <t-kristo@xxxxxx>
Cc: Kevin Hilman <khilman@xxxxxx>
Cc: Govindraj.R <govindraj.raja@xxxxxx>
---
arch/arm/mach-omap2/cpuidle34xx.c | 8 +++-----
arch/arm/mach-omap2/pm.h | 1 -
arch/arm/mach-omap2/pm34xx.c | 10 ----------
3 files changed, 3 insertions(+), 16 deletions(-)
diff --git a/arch/arm/mach-omap2/cpuidle34xx.c b/arch/arm/mach-omap2/cpuidle34xx.c
index 942bb4f..4ef32d4 100644
--- a/arch/arm/mach-omap2/cpuidle34xx.c
+++ b/arch/arm/mach-omap2/cpuidle34xx.c
@@ -183,6 +183,9 @@ static int next_valid_state(struct cpuidle_device *dev,
core_deepest_state = PWRDM_POWER_OFF;
}
+ if (!omap_uart_can_sleep())
+ core_deepest_state = PWRDM_POWER_ON;
+
/* Check if current state is valid */
if ((cx->valid) &&
(cx->mpu_state >= mpu_deepest_state) &&
@@ -244,11 +247,6 @@ static int omap3_enter_idle_bm(struct cpuidle_device *dev,
struct omap3_idle_statedata *cx;
int ret;
- if (!omap3_can_sleep()) {
- new_state_idx = drv->safe_state_index;
- goto select_state;
- }
-
/*
* Prevent idle completely if CAM is active.
* CAM does not have wakeup capability in OMAP3.
diff --git a/arch/arm/mach-omap2/pm.h b/arch/arm/mach-omap2/pm.h
index 4e166ad..eac6fce 100644
--- a/arch/arm/mach-omap2/pm.h
+++ b/arch/arm/mach-omap2/pm.h
@@ -18,7 +18,6 @@
extern void *omap3_secure_ram_storage;
extern void omap3_pm_off_mode_enable(int);
extern void omap_sram_idle(void);
-extern int omap3_can_sleep(void);
extern int omap_set_pwrdm_state(struct powerdomain *pwrdm, u32 state);
extern int omap3_idle_init(void);
diff --git a/arch/arm/mach-omap2/pm34xx.c b/arch/arm/mach-omap2/pm34xx.c
index efa6649..1c49824 100644
--- a/arch/arm/mach-omap2/pm34xx.c
+++ b/arch/arm/mach-omap2/pm34xx.c
@@ -484,21 +484,11 @@ console_still_active:
clkdm_allow_idle(mpu_pwrdm->pwrdm_clkdms[0]);
}
-int omap3_can_sleep(void)
-{
- if (!omap_uart_can_sleep())
- return 0;
- return 1;
-}
-
static void omap3_pm_idle(void)
{
local_irq_disable();
local_fiq_disable();
- if (!omap3_can_sleep())
- goto out;
-
if (omap_irq_pending() || need_resched())
goto out;
--
1.7.8.3
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