LinuxLists.cc - [PATCH v10 0/5] amba/dmaengine: pl330: add Power Management support

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Subject: [PATCH v10 1/5] PM / Runtime: Allow accessing irq_safe if no PM_RUNTIME

Some drivers (e.g. bus drivers) may want to check if power.irq_safe was
called by child driver, regardless of CONFIG_PM_RUNTIME.

An example scenario is amba/bus.c and dma/pl330.c drivers. The runtime
suspend/resume callbacks in amba bus driver act differently if irq_safe
was set by child driver (in irq_safe mode bus clock is only disabled).

The pl330 driver sets irq_safe and assumes that amba bus driver will
only disable the clock in runtime PM. So in system sleep suspend
callback the pl330 driver unprepares the clock after calling
pm_runtime_force_suspend().

However inconsistency would appear if CONFIG_PM_RUNTIME is not set and
child drivers do not want the irq_safe runtime PM. In such case amba bus
driver still has to know whether child driver wanted irq_safe - by
looking at dev->power.irq_safe field.

Signed-off-by: Krzysztof Kozlowski <[email protected]>
---
include/linux/pm.h | 2 +-
include/linux/pm_runtime.h | 5 ++++-
2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/include/linux/pm.h b/include/linux/pm.h
index 383fd68aaee1..b05fa954f50d 100644
--- a/include/linux/pm.h
+++ b/include/linux/pm.h
@@ -566,6 +566,7 @@ struct dev_pm_info {
bool ignore_children:1;
bool early_init:1; /* Owned by the PM core */
bool direct_complete:1; /* Owned by the PM core */
+ unsigned int irq_safe:1; /* PM runtime */
spinlock_t lock;
#ifdef CONFIG_PM_SLEEP
struct list_head entry;
@@ -590,7 +591,6 @@ struct dev_pm_info {
unsigned int run_wake:1;
unsigned int runtime_auto:1;
unsigned int no_callbacks:1;
- unsigned int irq_safe:1;
unsigned int use_autosuspend:1;
unsigned int timer_autosuspends:1;
unsigned int memalloc_noio:1;
diff --git a/include/linux/pm_runtime.h b/include/linux/pm_runtime.h
index 367f49b9a1c9..d94a65662a60 100644
--- a/include/linux/pm_runtime.h
+++ b/include/linux/pm_runtime.h
@@ -166,7 +166,10 @@ static inline bool pm_runtime_suspended_if_enabled(struct device *dev) { return
static inline bool pm_runtime_enabled(struct device *dev) { return false; }

static inline void pm_runtime_no_callbacks(struct device *dev) {}
-static inline void pm_runtime_irq_safe(struct device *dev) {}
+static inline void pm_runtime_irq_safe(struct device *dev)
+{
+ dev->power.irq_safe = 1;
+}

static inline bool pm_runtime_callbacks_present(struct device *dev) { return false; }
static inline void pm_runtime_mark_last_busy(struct device *dev) {}
--
1.9.1

2014-11-06 08:37:15

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Subject: [PATCH v10 2/5] amba: Add helpers for (un)preparing AMBA clock

Add amba_pclk_prepare() and amba_pclk_unprepare() inline functions for
handling the AMBA bus clock by device drivers.

Signed-off-by: Krzysztof Kozlowski <[email protected]>
Reviewed-by: Ulf Hansson <[email protected]>
---
include/linux/amba/bus.h | 10 ++++++++++
1 file changed, 10 insertions(+)

diff --git a/include/linux/amba/bus.h b/include/linux/amba/bus.h
index c324f5700d1a..ac02f9bd63dc 100644
--- a/include/linux/amba/bus.h
+++ b/include/linux/amba/bus.h
@@ -97,6 +97,16 @@ void amba_release_regions(struct amba_device *);
#define amba_pclk_disable(d) \
do { if (!IS_ERR((d)->pclk)) clk_disable((d)->pclk); } while (0)

+static inline int amba_pclk_prepare(struct amba_device *dev)
+{
+ return clk_prepare(dev->pclk);
+}
+
+static inline void amba_pclk_unprepare(struct amba_device *dev)
+{
+ clk_unprepare(dev->pclk);
+}
+
/* Some drivers don't use the struct amba_device */
#define AMBA_CONFIG_BITS(a) (((a) >> 24) & 0xff)
#define AMBA_REV_BITS(a) (((a) >> 20) & 0x0f)
--
1.9.1

2014-11-06 08:37:18

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Subject: [PATCH v10 5/5] amba: Remove unused amba_pclk_enable/disable macros

Remove the amba_pclk_enable and amba_pclk_disable macros because they
are not used by the drivers.

Signed-off-by: Krzysztof Kozlowski <[email protected]>
Reviewed-by: Ulf Hansson <[email protected]>
---
include/linux/amba/bus.h | 6 ------
1 file changed, 6 deletions(-)

diff --git a/include/linux/amba/bus.h b/include/linux/amba/bus.h
index c4bae79851fb..566adf0e0412 100644
--- a/include/linux/amba/bus.h
+++ b/include/linux/amba/bus.h
@@ -92,12 +92,6 @@ struct amba_device *amba_find_device(const char *, struct device *, unsigned int
int amba_request_regions(struct amba_device *, const char *);
void amba_release_regions(struct amba_device *);

-#define amba_pclk_enable(d) \
- (IS_ERR((d)->pclk) ? 0 : clk_enable((d)->pclk))
-
-#define amba_pclk_disable(d) \
- do { if (!IS_ERR((d)->pclk)) clk_disable((d)->pclk); } while (0)
-
static inline int amba_pclk_prepare(struct amba_device *dev)
{
return clk_prepare(dev->pclk);
--
1.9.1

2014-11-06 08:38:28

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Subject: [PATCH v10 3/5] amba: Don't unprepare the clocks if device driver wants IRQ safe runtime PM

The AMBA bus driver defines runtime Power Management functions which
disable and unprepare AMBA bus clock. This is problematic for runtime PM
because unpreparing a clock might sleep so it is not interrupt safe.

However some drivers may want to implement runtime PM functions in
interrupt-safe way (see pm_runtime_irq_safe()). In such case the AMBA
bus driver should only disable/enable the clock in runtime suspend and
resume callbacks.

Detect the device driver behavior during runtime suspend. During runtime
resume deal with clocks according to stored value.

Signed-off-by: Krzysztof Kozlowski <[email protected]>
---
drivers/amba/bus.c | 17 +++++++++++++----
include/linux/amba/bus.h | 1 +
2 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/drivers/amba/bus.c b/drivers/amba/bus.c
index 47bbdc1b5be3..356f906c6966 100644
--- a/drivers/amba/bus.c
+++ b/drivers/amba/bus.c
@@ -95,8 +95,14 @@ static int amba_pm_runtime_suspend(struct device *dev)
struct amba_device *pcdev = to_amba_device(dev);
int ret = pm_generic_runtime_suspend(dev);

- if (ret == 0 && dev->driver)
- clk_disable_unprepare(pcdev->pclk);
+ if (ret == 0 && dev->driver) {
+ pcdev->irq_safe = dev->power.irq_safe;
+
+ if (pcdev->irq_safe)
+ clk_disable(pcdev->pclk);
+ else
+ clk_disable_unprepare(pcdev->pclk);
+ }

return ret;
}
@@ -107,7 +113,10 @@ static int amba_pm_runtime_resume(struct device *dev)
int ret;

if (dev->driver) {
- ret = clk_prepare_enable(pcdev->pclk);
+ if (pcdev->irq_safe)
+ ret = clk_enable(pcdev->pclk);
+ else
+ ret = clk_prepare_enable(pcdev->pclk);
/* Failure is probably fatal to the system, but... */
if (ret)
return ret;
@@ -115,7 +124,7 @@ static int amba_pm_runtime_resume(struct device *dev)

return pm_generic_runtime_resume(dev);
}
-#endif
+#endif /* CONFIG_PM */

static const struct dev_pm_ops amba_pm = {
.suspend = pm_generic_suspend,
diff --git a/include/linux/amba/bus.h b/include/linux/amba/bus.h
index ac02f9bd63dc..c4bae79851fb 100644
--- a/include/linux/amba/bus.h
+++ b/include/linux/amba/bus.h
@@ -32,6 +32,7 @@ struct amba_device {
struct clk *pclk;
unsigned int periphid;
unsigned int irq[AMBA_NR_IRQS];
+ unsigned int irq_safe:1;
};

struct amba_driver {
--
1.9.1

2014-11-06 08:38:26

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Subject: [PATCH v10 4/5] dmaengine: pl330: add Power Management support

This patch adds both normal PM suspend/resume support and runtime PM
support to pl330 DMA engine driver.

The runtime power management for pl330 DMA driver allows gating of AMBA
clock (PDMA) in FSYS clock domain, when the device is not processing any
requests. This is necessary to enter low power modes on Exynos SoCs
(e.g. LPA on Exynos4x12 or W-AFTR on Exynos3250).

Runtime PM resuming of the device may happen in atomic context (during
call device_issue_pending()) so pm_runtime_irq_safe() is used. This will
lead only to disabling/enabling of the clock but this is sufficient for
gating the clock and for reducing energy usage.

During system sleep the AMBA bus clock is also unprepared.

Suggested-by: Bartlomiej Zolnierkiewicz <[email protected]>
Signed-off-by: Krzysztof Kozlowski <[email protected]>
Reviewed-by: Ulf Hansson <[email protected]>
---
drivers/dma/pl330.c | 96 ++++++++++++++++++++++++++++++++++++++++++++++++++---
1 file changed, 92 insertions(+), 4 deletions(-)

diff --git a/drivers/dma/pl330.c b/drivers/dma/pl330.c
index 4839bfa74a10..2bb0d08239bb 100644
--- a/drivers/dma/pl330.c
+++ b/drivers/dma/pl330.c
@@ -27,6 +27,7 @@
#include <linux/of.h>
#include <linux/of_dma.h>
#include <linux/err.h>
+#include <linux/pm_runtime.h>

#include "dmaengine.h"
#define PL330_MAX_CHAN 8
@@ -265,6 +266,9 @@ static unsigned cmd_line;

#define NR_DEFAULT_DESC 16

+/* Delay for runtime PM autosuspend, ms */
+#define PL330_AUTOSUSPEND_DELAY 20
+
/* Populated by the PL330 core driver for DMA API driver's info */
struct pl330_config {
u32 periph_id;
@@ -1958,6 +1962,7 @@ static void pl330_tasklet(unsigned long data)
struct dma_pl330_chan *pch = (struct dma_pl330_chan *)data;
struct dma_pl330_desc *desc, *_dt;
unsigned long flags;
+ bool power_down = false;

spin_lock_irqsave(&pch->lock, flags);

@@ -1972,10 +1977,17 @@ static void pl330_tasklet(unsigned long data)
/* Try to submit a req imm. next to the last completed cookie */
fill_queue(pch);

- /* Make sure the PL330 Channel thread is active */
- spin_lock(&pch->thread->dmac->lock);
- _start(pch->thread);
- spin_unlock(&pch->thread->dmac->lock);
+ if (list_empty(&pch->work_list)) {
+ spin_lock(&pch->thread->dmac->lock);
+ _stop(pch->thread);
+ spin_unlock(&pch->thread->dmac->lock);
+ power_down = true;
+ } else {
+ /* Make sure the PL330 Channel thread is active */
+ spin_lock(&pch->thread->dmac->lock);
+ _start(pch->thread);
+ spin_unlock(&pch->thread->dmac->lock);
+ }

while (!list_empty(&pch->completed_list)) {
dma_async_tx_callback callback;
@@ -1990,6 +2002,12 @@ static void pl330_tasklet(unsigned long data)
if (pch->cyclic) {
desc->status = PREP;
list_move_tail(&desc->node, &pch->work_list);
+ if (power_down) {
+ spin_lock(&pch->thread->dmac->lock);
+ _start(pch->thread);
+ spin_unlock(&pch->thread->dmac->lock);
+ power_down = false;
+ }
} else {
desc->status = FREE;
list_move_tail(&desc->node, &pch->dmac->desc_pool);
@@ -2004,6 +2022,12 @@ static void pl330_tasklet(unsigned long data)
}
}
spin_unlock_irqrestore(&pch->lock, flags);
+
+ /* If work list empty, power down */
+ if (power_down) {
+ pm_runtime_mark_last_busy(pch->dmac->ddma.dev);
+ pm_runtime_put_autosuspend(pch->dmac->ddma.dev);
+ }
}

bool pl330_filter(struct dma_chan *chan, void *param)
@@ -2073,6 +2097,7 @@ static int pl330_control(struct dma_chan *chan, enum dma_ctrl_cmd cmd, unsigned

switch (cmd) {
case DMA_TERMINATE_ALL:
+ pm_runtime_get_sync(pl330->ddma.dev);
spin_lock_irqsave(&pch->lock, flags);

spin_lock(&pl330->lock);
@@ -2099,10 +2124,15 @@ static int pl330_control(struct dma_chan *chan, enum dma_ctrl_cmd cmd, unsigned
dma_cookie_complete(&desc->txd);
}

+ if (!list_empty(&pch->work_list))
+ pm_runtime_put(pl330->ddma.dev);
+
list_splice_tail_init(&pch->submitted_list, &pl330->desc_pool);
list_splice_tail_init(&pch->work_list, &pl330->desc_pool);
list_splice_tail_init(&pch->completed_list, &pl330->desc_pool);
spin_unlock_irqrestore(&pch->lock, flags);
+ pm_runtime_mark_last_busy(pl330->ddma.dev);
+ pm_runtime_put_autosuspend(pl330->ddma.dev);
break;
case DMA_SLAVE_CONFIG:
slave_config = (struct dma_slave_config *)arg;
@@ -2138,6 +2168,7 @@ static void pl330_free_chan_resources(struct dma_chan *chan)

tasklet_kill(&pch->task);

+ pm_runtime_get_sync(pch->dmac->ddma.dev);
spin_lock_irqsave(&pch->lock, flags);

pl330_release_channel(pch->thread);
@@ -2147,6 +2178,8 @@ static void pl330_free_chan_resources(struct dma_chan *chan)
list_splice_tail_init(&pch->work_list, &pch->dmac->desc_pool);

spin_unlock_irqrestore(&pch->lock, flags);
+ pm_runtime_mark_last_busy(pch->dmac->ddma.dev);
+ pm_runtime_put_autosuspend(pch->dmac->ddma.dev);
}

static enum dma_status
@@ -2162,6 +2195,15 @@ static void pl330_issue_pending(struct dma_chan *chan)
unsigned long flags;

spin_lock_irqsave(&pch->lock, flags);
+ if (list_empty(&pch->work_list)) {
+ /*
+ * Warn on nothing pending. Empty submitted_list may
+ * break our pm_runtime usage counter as it is
+ * updated on work_list emptiness status.
+ */
+ WARN_ON(list_empty(&pch->submitted_list));
+ pm_runtime_get_sync(pch->dmac->ddma.dev);
+ }
list_splice_tail_init(&pch->submitted_list, &pch->work_list);
spin_unlock_irqrestore(&pch->lock, flags);

@@ -2585,6 +2627,43 @@ static int pl330_dma_device_slave_caps(struct dma_chan *dchan,
return 0;
}

+/*
+ * Runtime PM callbacks are provided by amba/bus.c driver.
+ *
+ * It is assumed here that IRQ safe runtime PM is chosen in probe and amba
+ * bus driver will only disable/enable the clock in runtime PM suspend/resume.
+ */
+static int __maybe_unused pl330_suspend(struct device *dev)
+{
+ struct amba_device *pcdev = to_amba_device(dev);
+ int ret;
+
+ ret = pm_runtime_force_suspend(dev);
+ if (ret)
+ return ret;
+
+ amba_pclk_unprepare(pcdev);
+
+ return 0;
+}
+
+static int __maybe_unused pl330_resume(struct device *dev)
+{
+ struct amba_device *pcdev = to_amba_device(dev);
+
+ amba_pclk_prepare(pcdev);
+
+ /*
+ * TODO: Idea for future. The device should not be woken up after
+ * system resume if it is not needed. It could stay runtime suspended
+ * waiting for DMA requests. However for safe suspend and resume we
+ * forcibly resume the device here.
+ */
+ return pm_runtime_force_resume(dev);
+}
+
+static SIMPLE_DEV_PM_OPS(pl330_pm, pl330_suspend, pl330_resume);
+
static int
pl330_probe(struct amba_device *adev, const struct amba_id *id)
{
@@ -2738,6 +2817,12 @@ pl330_probe(struct amba_device *adev, const struct amba_id *id)
pcfg->data_buf_dep, pcfg->data_bus_width / 8, pcfg->num_chan,
pcfg->num_peri, pcfg->num_events);

+ pm_runtime_irq_safe(&adev->dev);
+ pm_runtime_use_autosuspend(&adev->dev);
+ pm_runtime_set_autosuspend_delay(&adev->dev, PL330_AUTOSUSPEND_DELAY);
+ pm_runtime_mark_last_busy(&adev->dev);
+ pm_runtime_put_autosuspend(&adev->dev);
+
return 0;
probe_err3:
/* Idle the DMAC */
@@ -2764,6 +2849,8 @@ static int pl330_remove(struct amba_device *adev)
struct pl330_dmac *pl330 = amba_get_drvdata(adev);
struct dma_pl330_chan *pch, *_p;

+ pm_runtime_get_noresume(pl330->ddma.dev);
+
if (adev->dev.of_node)
of_dma_controller_free(adev->dev.of_node);

@@ -2802,6 +2889,7 @@ static struct amba_driver pl330_driver = {
.drv = {
.owner = THIS_MODULE,
.name = "dma-pl330",
+ .pm = &pl330_pm,
},
.id_table = pl330_ids,
.probe = pl330_probe,
--
1.9.1

2014-11-06 10:00:09

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Subject: Re: [PATCH v10 1/5] PM / Runtime: Allow accessing irq_safe if no PM_RUNTIME

On 6 November 2014 09:36, Krzysztof Kozlowski <[email protected]> wrote:
> Some drivers (e.g. bus drivers) may want to check if power.irq_safe was
> called by child driver, regardless of CONFIG_PM_RUNTIME.
>
> An example scenario is amba/bus.c and dma/pl330.c drivers. The runtime
> suspend/resume callbacks in amba bus driver act differently if irq_safe
> was set by child driver (in irq_safe mode bus clock is only disabled).
>
> The pl330 driver sets irq_safe and assumes that amba bus driver will
> only disable the clock in runtime PM. So in system sleep suspend
> callback the pl330 driver unprepares the clock after calling
> pm_runtime_force_suspend().
>
> However inconsistency would appear if CONFIG_PM_RUNTIME is not set and
> child drivers do not want the irq_safe runtime PM. In such case amba bus
> driver still has to know whether child driver wanted irq_safe - by
> looking at dev->power.irq_safe field.
>
> Signed-off-by: Krzysztof Kozlowski <[email protected]>

FWIW: Reviewed-by: Ulf Hansson <[email protected]>

Kind regards
Uffe

> ---
> include/linux/pm.h | 2 +-
> include/linux/pm_runtime.h | 5 ++++-
> 2 files changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/pm.h b/include/linux/pm.h
> index 383fd68aaee1..b05fa954f50d 100644
> --- a/include/linux/pm.h
> +++ b/include/linux/pm.h
> @@ -566,6 +566,7 @@ struct dev_pm_info {
> bool ignore_children:1;
> bool early_init:1; /* Owned by the PM core */
> bool direct_complete:1; /* Owned by the PM core */
> + unsigned int irq_safe:1; /* PM runtime */
> spinlock_t lock;
> #ifdef CONFIG_PM_SLEEP
> struct list_head entry;
> @@ -590,7 +591,6 @@ struct dev_pm_info {
> unsigned int run_wake:1;
> unsigned int runtime_auto:1;
> unsigned int no_callbacks:1;
> - unsigned int irq_safe:1;
> unsigned int use_autosuspend:1;
> unsigned int timer_autosuspends:1;
> unsigned int memalloc_noio:1;
> diff --git a/include/linux/pm_runtime.h b/include/linux/pm_runtime.h
> index 367f49b9a1c9..d94a65662a60 100644
> --- a/include/linux/pm_runtime.h
> +++ b/include/linux/pm_runtime.h
> @@ -166,7 +166,10 @@ static inline bool pm_runtime_suspended_if_enabled(struct device *dev) { return
> static inline bool pm_runtime_enabled(struct device *dev) { return false; }
>
> static inline void pm_runtime_no_callbacks(struct device *dev) {}
> -static inline void pm_runtime_irq_safe(struct device *dev) {}
> +static inline void pm_runtime_irq_safe(struct device *dev)
> +{
> + dev->power.irq_safe = 1;
> +}
>
> static inline bool pm_runtime_callbacks_present(struct device *dev) { return false; }
> static inline void pm_runtime_mark_last_busy(struct device *dev) {}
> --
> 1.9.1
>

2014-11-06 10:03:12

[permalink] [raw]

Subject: Re: [PATCH v10 3/5] amba: Don't unprepare the clocks if device driver wants IRQ safe runtime PM

On 6 November 2014 09:36, Krzysztof Kozlowski <[email protected]> wrote:
> The AMBA bus driver defines runtime Power Management functions which
> disable and unprepare AMBA bus clock. This is problematic for runtime PM
> because unpreparing a clock might sleep so it is not interrupt safe.
>
> However some drivers may want to implement runtime PM functions in
> interrupt-safe way (see pm_runtime_irq_safe()). In such case the AMBA
> bus driver should only disable/enable the clock in runtime suspend and
> resume callbacks.
>
> Detect the device driver behavior during runtime suspend. During runtime
> resume deal with clocks according to stored value.
>
> Signed-off-by: Krzysztof Kozlowski <[email protected]>

Reviewed-by: Ulf Hansson <[email protected]>

> ---
> drivers/amba/bus.c | 17 +++++++++++++----
> include/linux/amba/bus.h | 1 +
> 2 files changed, 14 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/amba/bus.c b/drivers/amba/bus.c
> index 47bbdc1b5be3..356f906c6966 100644
> --- a/drivers/amba/bus.c
> +++ b/drivers/amba/bus.c
> @@ -95,8 +95,14 @@ static int amba_pm_runtime_suspend(struct device *dev)
> struct amba_device *pcdev = to_amba_device(dev);
> int ret = pm_generic_runtime_suspend(dev);
>
> - if (ret == 0 && dev->driver)
> - clk_disable_unprepare(pcdev->pclk);
> + if (ret == 0 && dev->driver) {
> + pcdev->irq_safe = dev->power.irq_safe;
> +
> + if (pcdev->irq_safe)
> + clk_disable(pcdev->pclk);
> + else
> + clk_disable_unprepare(pcdev->pclk);
> + }
>
> return ret;
> }
> @@ -107,7 +113,10 @@ static int amba_pm_runtime_resume(struct device *dev)
> int ret;
>
> if (dev->driver) {
> - ret = clk_prepare_enable(pcdev->pclk);
> + if (pcdev->irq_safe)
> + ret = clk_enable(pcdev->pclk);
> + else
> + ret = clk_prepare_enable(pcdev->pclk);
> /* Failure is probably fatal to the system, but... */
> if (ret)
> return ret;
> @@ -115,7 +124,7 @@ static int amba_pm_runtime_resume(struct device *dev)
>
> return pm_generic_runtime_resume(dev);
> }
> -#endif
> +#endif /* CONFIG_PM */
>
> static const struct dev_pm_ops amba_pm = {
> .suspend = pm_generic_suspend,
> diff --git a/include/linux/amba/bus.h b/include/linux/amba/bus.h
> index ac02f9bd63dc..c4bae79851fb 100644
> --- a/include/linux/amba/bus.h
> +++ b/include/linux/amba/bus.h
> @@ -32,6 +32,7 @@ struct amba_device {
> struct clk *pclk;
> unsigned int periphid;
> unsigned int irq[AMBA_NR_IRQS];
> + unsigned int irq_safe:1;
> };
>
> struct amba_driver {
> --
> 1.9.1
>

2014-11-06 12:44:47

by Vinod Koul

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Subject: Re: [PATCH v10 4/5] dmaengine: pl330: add Power Management support

On Thu, Nov 06, 2014 at 09:36:49AM +0100, Krzysztof Kozlowski wrote:
> This patch adds both normal PM suspend/resume support and runtime PM
> support to pl330 DMA engine driver.
>
> The runtime power management for pl330 DMA driver allows gating of AMBA
> clock (PDMA) in FSYS clock domain, when the device is not processing any
> requests. This is necessary to enter low power modes on Exynos SoCs
> (e.g. LPA on Exynos4x12 or W-AFTR on Exynos3250).
>
> Runtime PM resuming of the device may happen in atomic context (during
> call device_issue_pending()) so pm_runtime_irq_safe() is used. This will
> lead only to disabling/enabling of the clock but this is sufficient for
> gating the clock and for reducing energy usage.
>
> During system sleep the AMBA bus clock is also unprepared.

Acked-by: Vinod Koul <[email protected]>

--
~Vinod

2014-11-06 22:30:20

[permalink] [raw]

Subject: Re: [PATCH v10 1/5] PM / Runtime: Allow accessing irq_safe if no PM_RUNTIME

On Thursday, November 06, 2014 09:36:46 AM Krzysztof Kozlowski wrote:
> Some drivers (e.g. bus drivers) may want to check if power.irq_safe was
> called by child driver, regardless of CONFIG_PM_RUNTIME.
>
> An example scenario is amba/bus.c and dma/pl330.c drivers. The runtime
> suspend/resume callbacks in amba bus driver act differently if irq_safe
> was set by child driver (in irq_safe mode bus clock is only disabled).
>
> The pl330 driver sets irq_safe and assumes that amba bus driver will
> only disable the clock in runtime PM. So in system sleep suspend
> callback the pl330 driver unprepares the clock after calling
> pm_runtime_force_suspend().
>
> However inconsistency would appear if CONFIG_PM_RUNTIME is not set and
> child drivers do not want the irq_safe runtime PM. In such case amba bus
> driver still has to know whether child driver wanted irq_safe - by
> looking at dev->power.irq_safe field.
>
> Signed-off-by: Krzysztof Kozlowski <[email protected]>
> ---
> include/linux/pm.h | 2 +-
> include/linux/pm_runtime.h | 5 ++++-
> 2 files changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/pm.h b/include/linux/pm.h
> index 383fd68aaee1..b05fa954f50d 100644
> --- a/include/linux/pm.h
> +++ b/include/linux/pm.h
> @@ -566,6 +566,7 @@ struct dev_pm_info {
> bool ignore_children:1;
> bool early_init:1; /* Owned by the PM core */
> bool direct_complete:1; /* Owned by the PM core */
> + unsigned int irq_safe:1; /* PM runtime */
> spinlock_t lock;
> #ifdef CONFIG_PM_SLEEP
> struct list_head entry;
> @@ -590,7 +591,6 @@ struct dev_pm_info {
> unsigned int run_wake:1;
> unsigned int runtime_auto:1;
> unsigned int no_callbacks:1;
> - unsigned int irq_safe:1;
> unsigned int use_autosuspend:1;
> unsigned int timer_autosuspends:1;
> unsigned int memalloc_noio:1;

Well, that is a good reason to introduce a wrapper around power.irq_safe in my
view.

And define the wrapper so that it always returns false for CONFIG_PM_RUNTIME
unset.

This way not only you wouldn't need to move the flag from under the #ifdef,
but also you would make the compiler skip the relevant pieces of code
entiretly for CONFIG_PM_RUNTIME unset.

> diff --git a/include/linux/pm_runtime.h b/include/linux/pm_runtime.h
> index 367f49b9a1c9..d94a65662a60 100644
> --- a/include/linux/pm_runtime.h
> +++ b/include/linux/pm_runtime.h
> @@ -166,7 +166,10 @@ static inline bool pm_runtime_suspended_if_enabled(struct device *dev) { return
> static inline bool pm_runtime_enabled(struct device *dev) { return false; }
>
> static inline void pm_runtime_no_callbacks(struct device *dev) {}
> -static inline void pm_runtime_irq_safe(struct device *dev) {}
> +static inline void pm_runtime_irq_safe(struct device *dev)
> +{
> + dev->power.irq_safe = 1;
> +}
>
> static inline bool pm_runtime_callbacks_present(struct device *dev) { return false; }
> static inline void pm_runtime_mark_last_busy(struct device *dev) {}
>

--
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.

2014-11-06 22:31:31

[permalink] [raw]

Subject: Re: [PATCH v10 3/5] amba: Don't unprepare the clocks if device driver wants IRQ safe runtime PM

On Thursday, November 06, 2014 09:36:48 AM Krzysztof Kozlowski wrote:
> The AMBA bus driver defines runtime Power Management functions which
> disable and unprepare AMBA bus clock. This is problematic for runtime PM
> because unpreparing a clock might sleep so it is not interrupt safe.
>
> However some drivers may want to implement runtime PM functions in
> interrupt-safe way (see pm_runtime_irq_safe()). In such case the AMBA
> bus driver should only disable/enable the clock in runtime suspend and
> resume callbacks.
>
> Detect the device driver behavior during runtime suspend. During runtime
> resume deal with clocks according to stored value.
>
> Signed-off-by: Krzysztof Kozlowski <[email protected]>
> ---
> drivers/amba/bus.c | 17 +++++++++++++----
> include/linux/amba/bus.h | 1 +
> 2 files changed, 14 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/amba/bus.c b/drivers/amba/bus.c
> index 47bbdc1b5be3..356f906c6966 100644
> --- a/drivers/amba/bus.c
> +++ b/drivers/amba/bus.c
> @@ -95,8 +95,14 @@ static int amba_pm_runtime_suspend(struct device *dev)
> struct amba_device *pcdev = to_amba_device(dev);
> int ret = pm_generic_runtime_suspend(dev);
>
> - if (ret == 0 && dev->driver)
> - clk_disable_unprepare(pcdev->pclk);
> + if (ret == 0 && dev->driver) {
> + pcdev->irq_safe = dev->power.irq_safe;
> +
> + if (pcdev->irq_safe)
> + clk_disable(pcdev->pclk);
> + else
> + clk_disable_unprepare(pcdev->pclk);
> + }
>
> return ret;
> }
> @@ -107,7 +113,10 @@ static int amba_pm_runtime_resume(struct device *dev)
> int ret;
>
> if (dev->driver) {
> - ret = clk_prepare_enable(pcdev->pclk);
> + if (pcdev->irq_safe)
> + ret = clk_enable(pcdev->pclk);
> + else
> + ret = clk_prepare_enable(pcdev->pclk);
> /* Failure is probably fatal to the system, but... */
> if (ret)
> return ret;
> @@ -115,7 +124,7 @@ static int amba_pm_runtime_resume(struct device *dev)
>
> return pm_generic_runtime_resume(dev);
> }
> -#endif
> +#endif /* CONFIG_PM */
>
> static const struct dev_pm_ops amba_pm = {
> .suspend = pm_generic_suspend,
> diff --git a/include/linux/amba/bus.h b/include/linux/amba/bus.h
> index ac02f9bd63dc..c4bae79851fb 100644
> --- a/include/linux/amba/bus.h
> +++ b/include/linux/amba/bus.h
> @@ -32,6 +32,7 @@ struct amba_device {
> struct clk *pclk;
> unsigned int periphid;
> unsigned int irq[AMBA_NR_IRQS];
> + unsigned int irq_safe:1;

Why do we need the new flag? Seems redundant to me.

> };
>
> struct amba_driver {
>

--
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.

2014-11-07 08:01:16

[permalink] [raw]

Subject: Re: [PATCH v10 3/5] amba: Don't unprepare the clocks if device driver wants IRQ safe runtime PM

On czw, 2014-11-06 at 23:52 +0100, Rafael J. Wysocki wrote:
> On Thursday, November 06, 2014 09:36:48 AM Krzysztof Kozlowski wrote:
> > The AMBA bus driver defines runtime Power Management functions which
> > disable and unprepare AMBA bus clock. This is problematic for runtime PM
> > because unpreparing a clock might sleep so it is not interrupt safe.
> >
> > However some drivers may want to implement runtime PM functions in
> > interrupt-safe way (see pm_runtime_irq_safe()). In such case the AMBA
> > bus driver should only disable/enable the clock in runtime suspend and
> > resume callbacks.
> >
> > Detect the device driver behavior during runtime suspend. During runtime
> > resume deal with clocks according to stored value.
> >
> > Signed-off-by: Krzysztof Kozlowski <[email protected]>
> > ---
> > drivers/amba/bus.c | 17 +++++++++++++----
> > include/linux/amba/bus.h | 1 +
> > 2 files changed, 14 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/amba/bus.c b/drivers/amba/bus.c
> > index 47bbdc1b5be3..356f906c6966 100644
> > --- a/drivers/amba/bus.c
> > +++ b/drivers/amba/bus.c
> > @@ -95,8 +95,14 @@ static int amba_pm_runtime_suspend(struct device *dev)
> > struct amba_device *pcdev = to_amba_device(dev);
> > int ret = pm_generic_runtime_suspend(dev);
> >
> > - if (ret == 0 && dev->driver)
> > - clk_disable_unprepare(pcdev->pclk);
> > + if (ret == 0 && dev->driver) {
> > + pcdev->irq_safe = dev->power.irq_safe;
> > +
> > + if (pcdev->irq_safe)
> > + clk_disable(pcdev->pclk);
> > + else
> > + clk_disable_unprepare(pcdev->pclk);
> > + }
> >
> > return ret;
> > }
> > @@ -107,7 +113,10 @@ static int amba_pm_runtime_resume(struct device *dev)
> > int ret;
> >
> > if (dev->driver) {
> > - ret = clk_prepare_enable(pcdev->pclk);
> > + if (pcdev->irq_safe)
> > + ret = clk_enable(pcdev->pclk);
> > + else
> > + ret = clk_prepare_enable(pcdev->pclk);
> > /* Failure is probably fatal to the system, but... */
> > if (ret)
> > return ret;
> > @@ -115,7 +124,7 @@ static int amba_pm_runtime_resume(struct device *dev)
> >
> > return pm_generic_runtime_resume(dev);
> > }
> > -#endif
> > +#endif /* CONFIG_PM */
> >
> > static const struct dev_pm_ops amba_pm = {
> > .suspend = pm_generic_suspend,
> > diff --git a/include/linux/amba/bus.h b/include/linux/amba/bus.h
> > index ac02f9bd63dc..c4bae79851fb 100644
> > --- a/include/linux/amba/bus.h
> > +++ b/include/linux/amba/bus.h
> > @@ -32,6 +32,7 @@ struct amba_device {
> > struct clk *pclk;
> > unsigned int periphid;
> > unsigned int irq[AMBA_NR_IRQS];
> > + unsigned int irq_safe:1;
>
> Why do we need the new flag? Seems redundant to me.

Some poorly written driver could set irq_safe somewhere between suspend
and resume (e.g. in suspend callback).

Best regards,
Krzysztof

2014-11-07 08:06:49

[permalink] [raw]

Subject: Re: [PATCH v10 1/5] PM / Runtime: Allow accessing irq_safe if no PM_RUNTIME

On czw, 2014-11-06 at 23:51 +0100, Rafael J. Wysocki wrote:
> On Thursday, November 06, 2014 09:36:46 AM Krzysztof Kozlowski wrote:
> > Some drivers (e.g. bus drivers) may want to check if power.irq_safe was
> > called by child driver, regardless of CONFIG_PM_RUNTIME.
> >
> > An example scenario is amba/bus.c and dma/pl330.c drivers. The runtime
> > suspend/resume callbacks in amba bus driver act differently if irq_safe
> > was set by child driver (in irq_safe mode bus clock is only disabled).
> >
> > The pl330 driver sets irq_safe and assumes that amba bus driver will
> > only disable the clock in runtime PM. So in system sleep suspend
> > callback the pl330 driver unprepares the clock after calling
> > pm_runtime_force_suspend().
> >
> > However inconsistency would appear if CONFIG_PM_RUNTIME is not set and
> > child drivers do not want the irq_safe runtime PM. In such case amba bus
> > driver still has to know whether child driver wanted irq_safe - by
> > looking at dev->power.irq_safe field.
> >
> > Signed-off-by: Krzysztof Kozlowski <[email protected]>
> > ---
> > include/linux/pm.h | 2 +-
> > include/linux/pm_runtime.h | 5 ++++-
> > 2 files changed, 5 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/linux/pm.h b/include/linux/pm.h
> > index 383fd68aaee1..b05fa954f50d 100644
> > --- a/include/linux/pm.h
> > +++ b/include/linux/pm.h
> > @@ -566,6 +566,7 @@ struct dev_pm_info {
> > bool ignore_children:1;
> > bool early_init:1; /* Owned by the PM core */
> > bool direct_complete:1; /* Owned by the PM core */
> > + unsigned int irq_safe:1; /* PM runtime */
> > spinlock_t lock;
> > #ifdef CONFIG_PM_SLEEP
> > struct list_head entry;
> > @@ -590,7 +591,6 @@ struct dev_pm_info {
> > unsigned int run_wake:1;
> > unsigned int runtime_auto:1;
> > unsigned int no_callbacks:1;
> > - unsigned int irq_safe:1;
> > unsigned int use_autosuspend:1;
> > unsigned int timer_autosuspends:1;
> > unsigned int memalloc_noio:1;
>
> Well, that is a good reason to introduce a wrapper around power.irq_safe in my
> view.
>
> And define the wrapper so that it always returns false for CONFIG_PM_RUNTIME
> unset.
>
> This way not only you wouldn't need to move the flag from under the #ifdef,
> but also you would make the compiler skip the relevant pieces of code
> entiretly for CONFIG_PM_RUNTIME unset.

Few days ago I would be happy with your opinion :), but know I think
this is better solution than wrapper. Consider case:
1. PM_RUNTIME unset.
2. System suspends.
3. The pl330 in its suspend callback calls force_runtime_suspend which
leads us to amba/bus.
4. The amba/bus.c in runtime suspend checks for irq_safe (it is FALSE),
so it disables and unprepares the clock.
5. The pl330 in probe requested irq_safe so it assumes amba/bus will
only disable the clock. So the pl330 unprepares the clock. Again.

Best regards,
Krzysztof

2014-11-07 14:51:02

by Alan Stern

[permalink] [raw]

Subject: Re: [PATCH v10 1/5] PM / Runtime: Allow accessing irq_safe if no PM_RUNTIME

On Fri, 7 Nov 2014, Krzysztof Kozlowski wrote:

> > Well, that is a good reason to introduce a wrapper around power.irq_safe in my
> > view.
> >
> > And define the wrapper so that it always returns false for CONFIG_PM_RUNTIME
> > unset.
> >
> > This way not only you wouldn't need to move the flag from under the #ifdef,
> > but also you would make the compiler skip the relevant pieces of code
> > entiretly for CONFIG_PM_RUNTIME unset.
>
> Few days ago I would be happy with your opinion :), but know I think
> this is better solution than wrapper. Consider case:
> 1. PM_RUNTIME unset.
> 2. System suspends.
> 3. The pl330 in its suspend callback calls force_runtime_suspend which
> leads us to amba/bus.
> 4. The amba/bus.c in runtime suspend checks for irq_safe (it is FALSE),
> so it disables and unprepares the clock.
> 5. The pl330 in probe requested irq_safe so it assumes amba/bus will
> only disable the clock. So the pl330 unprepares the clock. Again.

To me, this sounds like a good reason to avoid using
force_runtime_suspend(). In fact, it sounds like a good reason to
avoid relying on the runtime PM mechanism to handle non-runtime-PM
things (like a system suspend callback). If CONFIG_PM_RUNTIME isn't
enabled then the runtime PM stack simply should not be used.

Alan Stern

2014-11-07 23:25:07

[permalink] [raw]

Subject: Re: [PATCH v10 1/5] PM / Runtime: Allow accessing irq_safe if no PM_RUNTIME

On Friday, November 07, 2014 09:50:58 AM Alan Stern wrote:
> On Fri, 7 Nov 2014, Krzysztof Kozlowski wrote:
>
> > > Well, that is a good reason to introduce a wrapper around power.irq_safe in my
> > > view.
> > >
> > > And define the wrapper so that it always returns false for CONFIG_PM_RUNTIME
> > > unset.
> > >
> > > This way not only you wouldn't need to move the flag from under the #ifdef,
> > > but also you would make the compiler skip the relevant pieces of code
> > > entiretly for CONFIG_PM_RUNTIME unset.
> >
> > Few days ago I would be happy with your opinion :), but know I think
> > this is better solution than wrapper. Consider case:
> > 1. PM_RUNTIME unset.
> > 2. System suspends.
> > 3. The pl330 in its suspend callback calls force_runtime_suspend which
> > leads us to amba/bus.
> > 4. The amba/bus.c in runtime suspend checks for irq_safe (it is FALSE),
> > so it disables and unprepares the clock.
> > 5. The pl330 in probe requested irq_safe so it assumes amba/bus will
> > only disable the clock. So the pl330 unprepares the clock. Again.
>
> To me, this sounds like a good reason to avoid using
> force_runtime_suspend(). In fact, it sounds like a good reason to
> avoid relying on the runtime PM mechanism to handle non-runtime-PM
> things (like a system suspend callback). If CONFIG_PM_RUNTIME isn't
> enabled then the runtime PM stack simply should not be used.

Amen.

2014-11-07 23:31:51

[permalink] [raw]

Subject: Re: [PATCH v10 3/5] amba: Don't unprepare the clocks if device driver wants IRQ safe runtime PM

On Friday, November 07, 2014 09:01:09 AM Krzysztof Kozlowski wrote:
> On czw, 2014-11-06 at 23:52 +0100, Rafael J. Wysocki wrote:
> > On Thursday, November 06, 2014 09:36:48 AM Krzysztof Kozlowski wrote:
> > > The AMBA bus driver defines runtime Power Management functions which
> > > disable and unprepare AMBA bus clock. This is problematic for runtime PM
> > > because unpreparing a clock might sleep so it is not interrupt safe.
> > >
> > > However some drivers may want to implement runtime PM functions in
> > > interrupt-safe way (see pm_runtime_irq_safe()). In such case the AMBA
> > > bus driver should only disable/enable the clock in runtime suspend and
> > > resume callbacks.
> > >
> > > Detect the device driver behavior during runtime suspend. During runtime
> > > resume deal with clocks according to stored value.
> > >
> > > Signed-off-by: Krzysztof Kozlowski <[email protected]>
> > > ---
> > > drivers/amba/bus.c | 17 +++++++++++++----
> > > include/linux/amba/bus.h | 1 +
> > > 2 files changed, 14 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/drivers/amba/bus.c b/drivers/amba/bus.c
> > > index 47bbdc1b5be3..356f906c6966 100644
> > > --- a/drivers/amba/bus.c
> > > +++ b/drivers/amba/bus.c
> > > @@ -95,8 +95,14 @@ static int amba_pm_runtime_suspend(struct device *dev)
> > > struct amba_device *pcdev = to_amba_device(dev);
> > > int ret = pm_generic_runtime_suspend(dev);
> > >
> > > - if (ret == 0 && dev->driver)
> > > - clk_disable_unprepare(pcdev->pclk);
> > > + if (ret == 0 && dev->driver) {
> > > + pcdev->irq_safe = dev->power.irq_safe;
> > > +
> > > + if (pcdev->irq_safe)
> > > + clk_disable(pcdev->pclk);
> > > + else
> > > + clk_disable_unprepare(pcdev->pclk);
> > > + }
> > >
> > > return ret;
> > > }
> > > @@ -107,7 +113,10 @@ static int amba_pm_runtime_resume(struct device *dev)
> > > int ret;
> > >
> > > if (dev->driver) {
> > > - ret = clk_prepare_enable(pcdev->pclk);
> > > + if (pcdev->irq_safe)
> > > + ret = clk_enable(pcdev->pclk);
> > > + else
> > > + ret = clk_prepare_enable(pcdev->pclk);
> > > /* Failure is probably fatal to the system, but... */
> > > if (ret)
> > > return ret;
> > > @@ -115,7 +124,7 @@ static int amba_pm_runtime_resume(struct device *dev)
> > >
> > > return pm_generic_runtime_resume(dev);
> > > }
> > > -#endif
> > > +#endif /* CONFIG_PM */
> > >
> > > static const struct dev_pm_ops amba_pm = {
> > > .suspend = pm_generic_suspend,
> > > diff --git a/include/linux/amba/bus.h b/include/linux/amba/bus.h
> > > index ac02f9bd63dc..c4bae79851fb 100644
> > > --- a/include/linux/amba/bus.h
> > > +++ b/include/linux/amba/bus.h
> > > @@ -32,6 +32,7 @@ struct amba_device {
> > > struct clk *pclk;
> > > unsigned int periphid;
> > > unsigned int irq[AMBA_NR_IRQS];
> > > + unsigned int irq_safe:1;
> >
> > Why do we need the new flag? Seems redundant to me.
>
> Some poorly written driver could set irq_safe somewhere between suspend
> and resume (e.g. in suspend callback).

It could also modify your bus type irq_safe flag to hide the fact. In my
opinion, it doesn't really help.

Rafael

2014-11-10 13:38:14

[permalink] [raw]

Subject: Re: [PATCH v10 1/5] PM / Runtime: Allow accessing irq_safe if no PM_RUNTIME

On 7 November 2014 09:06, Krzysztof Kozlowski <[email protected]> wrote:
> On czw, 2014-11-06 at 23:51 +0100, Rafael J. Wysocki wrote:
>> On Thursday, November 06, 2014 09:36:46 AM Krzysztof Kozlowski wrote:
>> > Some drivers (e.g. bus drivers) may want to check if power.irq_safe was
>> > called by child driver, regardless of CONFIG_PM_RUNTIME.
>> >
>> > An example scenario is amba/bus.c and dma/pl330.c drivers. The runtime
>> > suspend/resume callbacks in amba bus driver act differently if irq_safe
>> > was set by child driver (in irq_safe mode bus clock is only disabled).
>> >
>> > The pl330 driver sets irq_safe and assumes that amba bus driver will
>> > only disable the clock in runtime PM. So in system sleep suspend
>> > callback the pl330 driver unprepares the clock after calling
>> > pm_runtime_force_suspend().
>> >
>> > However inconsistency would appear if CONFIG_PM_RUNTIME is not set and
>> > child drivers do not want the irq_safe runtime PM. In such case amba bus
>> > driver still has to know whether child driver wanted irq_safe - by
>> > looking at dev->power.irq_safe field.
>> >
>> > Signed-off-by: Krzysztof Kozlowski <[email protected]>
>> > ---
>> > include/linux/pm.h | 2 +-
>> > include/linux/pm_runtime.h | 5 ++++-
>> > 2 files changed, 5 insertions(+), 2 deletions(-)
>> >
>> > diff --git a/include/linux/pm.h b/include/linux/pm.h
>> > index 383fd68aaee1..b05fa954f50d 100644
>> > --- a/include/linux/pm.h
>> > +++ b/include/linux/pm.h
>> > @@ -566,6 +566,7 @@ struct dev_pm_info {
>> > bool ignore_children:1;
>> > bool early_init:1; /* Owned by the PM core */
>> > bool direct_complete:1; /* Owned by the PM core */
>> > + unsigned int irq_safe:1; /* PM runtime */
>> > spinlock_t lock;
>> > #ifdef CONFIG_PM_SLEEP
>> > struct list_head entry;
>> > @@ -590,7 +591,6 @@ struct dev_pm_info {
>> > unsigned int run_wake:1;
>> > unsigned int runtime_auto:1;
>> > unsigned int no_callbacks:1;
>> > - unsigned int irq_safe:1;
>> > unsigned int use_autosuspend:1;
>> > unsigned int timer_autosuspends:1;
>> > unsigned int memalloc_noio:1;
>>
>> Well, that is a good reason to introduce a wrapper around power.irq_safe in my
>> view.
>>
>> And define the wrapper so that it always returns false for CONFIG_PM_RUNTIME
>> unset.
>>
>> This way not only you wouldn't need to move the flag from under the #ifdef,
>> but also you would make the compiler skip the relevant pieces of code
>> entiretly for CONFIG_PM_RUNTIME unset.
>
> Few days ago I would be happy with your opinion :), but know I think
> this is better solution than wrapper. Consider case:
> 1. PM_RUNTIME unset.
> 2. System suspends.
> 3. The pl330 in its suspend callback calls force_runtime_suspend which
> leads us to amba/bus.
> 4. The amba/bus.c in runtime suspend checks for irq_safe (it is FALSE),
> so it disables and unprepares the clock.
> 5. The pl330 in probe requested irq_safe so it assumes amba/bus will
> only disable the clock. So the pl330 unprepares the clock. Again.

This is easy to solve, still by using Rafael's approach.

In the pl330 system PM callbacks, you need to check
"pm_runtime_is_irqsafe()" or whatever the wrapper would be called.
When it returns true, that's when you should do
clk_prepare|unprepare().

I think that would be quite nice.

Kind regards
Uffe

2014-11-10 13:43:14

by Srikanth K

[permalink] [raw]

Subject: Re: [PATCH v10 1/5] PM / Runtime: Allow accessing irq_safe if no PM_RUNTIME

unsubscribe

2014-11-10 14:11:48

[permalink] [raw]

Subject: Re: [PATCH v10 1/5] PM / Runtime: Allow accessing irq_safe if no PM_RUNTIME

On 7 November 2014 15:50, Alan Stern <[email protected]> wrote:
> On Fri, 7 Nov 2014, Krzysztof Kozlowski wrote:
>
>> > Well, that is a good reason to introduce a wrapper around power.irq_safe in my
>> > view.
>> >
>> > And define the wrapper so that it always returns false for CONFIG_PM_RUNTIME
>> > unset.
>> >
>> > This way not only you wouldn't need to move the flag from under the #ifdef,
>> > but also you would make the compiler skip the relevant pieces of code
>> > entiretly for CONFIG_PM_RUNTIME unset.
>>
>> Few days ago I would be happy with your opinion :), but know I think
>> this is better solution than wrapper. Consider case:
>> 1. PM_RUNTIME unset.
>> 2. System suspends.
>> 3. The pl330 in its suspend callback calls force_runtime_suspend which
>> leads us to amba/bus.
>> 4. The amba/bus.c in runtime suspend checks for irq_safe (it is FALSE),
>> so it disables and unprepares the clock.
>> 5. The pl330 in probe requested irq_safe so it assumes amba/bus will
>> only disable the clock. So the pl330 unprepares the clock. Again.
>
> To me, this sounds like a good reason to avoid using
> force_runtime_suspend(). In fact, it sounds like a good reason to
> avoid relying on the runtime PM mechanism to handle non-runtime-PM
> things (like a system suspend callback). If CONFIG_PM_RUNTIME isn't
> enabled then the runtime PM stack simply should not be used.

There are an important advantage of using the pm_runtime_force_suspend() here.

For the driver to handle clock gating at system PM suspend, it first
needs to bring the device into full power, through
pm_runtime_get_sync(). Otherwise it's not safe to gate the clock,
since it may already be gated.

Kind regards
Uffe

2014-11-10 16:36:13

by Alan Stern

[permalink] [raw]

Subject: Re: [PATCH v10 1/5] PM / Runtime: Allow accessing irq_safe if no PM_RUNTIME

On Mon, 10 Nov 2014, Ulf Hansson wrote:

> > To me, this sounds like a good reason to avoid using
> > force_runtime_suspend(). In fact, it sounds like a good reason to
> > avoid relying on the runtime PM mechanism to handle non-runtime-PM
> > things (like a system suspend callback). If CONFIG_PM_RUNTIME isn't
> > enabled then the runtime PM stack simply should not be used.
>
> There are an important advantage of using the pm_runtime_force_suspend() here.
>
> For the driver to handle clock gating at system PM suspend, it first
> needs to bring the device into full power, through
> pm_runtime_get_sync(). Otherwise it's not safe to gate the clock,
> since it may already be gated.

That's fine, but it has nothing to do with pm_runtime_force_suspend().

Besides, if the real question is whether or not to gate the clock (or
in other words, has the clock already been gated), why not just store a
"clock_is_gated" flag somewhere?

Alan Stern

2014-11-10 18:35:45