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Message-ID: <569E1366.8070005@nvidia.com>
Date: Tue, 19 Jan 2016 10:43:50 +0000
From: Jon Hunter <jonathanh@...dia.com>
To: Ulf Hansson <ulf.hansson@...aro.org>
CC: Thomas Gleixner <tglx@...utronix.de>,
Jason Cooper <jason@...edaemon.net>,
Marc Zyngier <marc.zyngier@....com>,
Jiang Liu <jiang.liu@...ux.intel.com>,
Stephen Warren <swarren@...dotorg.org>,
Thierry Reding <thierry.reding@...il.com>,
Kevin Hilman <khilman@...nel.org>,
"Geert Uytterhoeven" <geert@...ux-m68k.org>,
Grygorii Strashko <grygorii.strashko@...com>,
Lars-Peter Clausen <lars@...afoo.de>,
"Linus Walleij" <linus.walleij@...aro.org>,
Soren Brinkmann <soren.brinkmann@...inx.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
"Rafael J. Wysocki" <rjw@...ysocki.net>
Subject: Re: [RFC PATCH V2 3/8] genirq: Add runtime power management support
for IRQ chips
On 18/01/16 14:47, Ulf Hansson wrote:
> +linux-pm, Rafael
>
> On 17 December 2015 at 11:48, Jon Hunter <jonathanh@...dia.com> wrote:
>> Some IRQ chips may be located in a power domain outside of the CPU
>> subsystem and hence will require device specific runtime power management.
>> In order to support such IRQ chips, add a pointer for a device structure
>> to the irq_chip structure, and if this pointer is populated by the IRQ
>> chip driver and the flag CHIP_HAS_RPM is set, then the pm_runtime_get/put
>> APIs for this chip will be called when an IRQ is requested/freed,
>> respectively.
>
> Overall I like the idea of this patch(set), as it will allow us to
> save power for "unused" irqchips.
Great, thanks.
>>
>> Signed-off-by: Jon Hunter <jonathanh@...dia.com>
>> ---
>> include/linux/irq.h | 4 ++++
>> kernel/irq/internals.h | 24 ++++++++++++++++++++++++
>> kernel/irq/manage.c | 7 +++++++
>> 3 files changed, 35 insertions(+)
>>
>> diff --git a/include/linux/irq.h b/include/linux/irq.h
>> index 3c1c96786248..7a61a7f76177 100644
>> --- a/include/linux/irq.h
>> +++ b/include/linux/irq.h
>> @@ -307,6 +307,7 @@ static inline irq_hw_number_t irqd_to_hwirq(struct irq_data *d)
>> /**
>> * struct irq_chip - hardware interrupt chip descriptor
>> *
>> + * @dev: pointer to associated device
>> * @name: name for /proc/interrupts
>> * @irq_startup: start up the interrupt (defaults to ->enable if NULL)
>> * @irq_shutdown: shut down the interrupt (defaults to ->disable if NULL)
>> @@ -344,6 +345,7 @@ static inline irq_hw_number_t irqd_to_hwirq(struct irq_data *d)
>> * @flags: chip specific flags
>> */
>> struct irq_chip {
>> + struct device *dev;
>> const char *name;
>> unsigned int (*irq_startup)(struct irq_data *data);
>> void (*irq_shutdown)(struct irq_data *data);
>> @@ -399,6 +401,7 @@ struct irq_chip {
>> * IRQCHIP_SKIP_SET_WAKE: Skip chip.irq_set_wake(), for this irq chip
>> * IRQCHIP_ONESHOT_SAFE: One shot does not require mask/unmask
>> * IRQCHIP_EOI_THREADED: Chip requires eoi() on unmask in threaded mode
>> + * IRQCHIP_HAS_PM: Chip requires runtime power management
>
> Perhaps we don't need to add a specific flag for this, but instead
> just check if the ->dev pointer has been assigned and then perform
> runtime PM management?
Yes it may not be necessary. However, I was not sure if someone would
make use of the dev structure but not use RPM. For now we could drop it.
>> */
>> enum {
>> IRQCHIP_SET_TYPE_MASKED = (1 << 0),
>> @@ -408,6 +411,7 @@ enum {
>> IRQCHIP_SKIP_SET_WAKE = (1 << 4),
>> IRQCHIP_ONESHOT_SAFE = (1 << 5),
>> IRQCHIP_EOI_THREADED = (1 << 6),
>> + IRQCHIP_HAS_RPM = (1 << 7),
>> };
>>
>> #include <linux/irqdesc.h>
>> diff --git a/kernel/irq/internals.h b/kernel/irq/internals.h
>> index fcab63c66905..30a2add7cae6 100644
>> --- a/kernel/irq/internals.h
>> +++ b/kernel/irq/internals.h
>> @@ -7,6 +7,7 @@
>> */
>> #include <linux/irqdesc.h>
>> #include <linux/kernel_stat.h>
>> +#include <linux/pm_runtime.h>
>>
>> #ifdef CONFIG_SPARSE_IRQ
>> # define IRQ_BITMAP_BITS (NR_IRQS + 8196)
>> @@ -125,6 +126,29 @@ static inline void chip_bus_sync_unlock(struct irq_desc *desc)
>> desc->irq_data.chip->irq_bus_sync_unlock(&desc->irq_data);
>> }
>>
>> +/* Inline functions for support of irq chips that require runtime pm */
>> +static inline int chip_pm_get(struct irq_desc *desc)
>
> Why does these new get/put functions need to be inline functions and
> thus defined in the header file? Perhaps move them to manage.c are
> better?
They don't have to be, and so I can move them.
>> +{
>> + int retval = 0;
>> +
>> + if (desc->irq_data.chip->dev &&
>> + desc->irq_data.chip->flags & IRQCHIP_HAS_RPM)
>> + retval = pm_runtime_get_sync(desc->irq_data.chip->dev);
>> +
>> + return (retval < 0) ? retval : 0;
>> +}
>> +
>> +static inline int chip_pm_put(struct irq_desc *desc)
>> +{
>> + int retval = 0;
>> +
>> + if (desc->irq_data.chip->dev &&
>> + desc->irq_data.chip->flags & IRQCHIP_HAS_RPM)
>> + retval = pm_runtime_put(desc->irq_data.chip->dev);
>> +
>> + return (retval < 0) ? retval : 0;
>
> This won't play nicely when CONFIG_PM is unset, as pm_runtime_put()
> would return -ENOSYS. In such cases I guess you would like to ignore
> the error!?
Ok, yes good point.
>> +}
>> +
>> #define _IRQ_DESC_CHECK (1 << 0)
>> #define _IRQ_DESC_PERCPU (1 << 1)
>>
>> diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
>> index 2a429b061171..8a96e4f1e985 100644
>> --- a/kernel/irq/manage.c
>> +++ b/kernel/irq/manage.c
>> @@ -1116,6 +1116,10 @@ __setup_irq(unsigned int irq, struct irq_desc *desc, struct irqaction *new)
>> if (!try_module_get(desc->owner))
>> return -ENODEV;
>>
>> + ret = chip_pm_get(desc);
>> + if (ret < 0)
>> + return ret;
>> +
>> new->irq = irq;
>>
>> /*
>> @@ -1400,6 +1404,7 @@ out_thread:
>> put_task_struct(t);
>> }
>> out_mput:
>> + chip_pm_put(desc);
>> module_put(desc->owner);
>> return ret;
>> }
>> @@ -1513,6 +1518,7 @@ static struct irqaction *__free_irq(unsigned int irq, void *dev_id)
>> }
>> }
>
> I don't think using __free_irq() is the correct place to decrease the
> runtime PM usage count. It will keep the irqchip runtime resumed even
> if there are no irqs enabled for it.
>
> Instead I would rather allow the irqchip to be runtime suspended, when
> there are no irqs enabled on it.
>
> Therefore you should rather use __enable|disable_irq() from where you
> increase/decrease the runtime PM usage count.
>
> Although, I realize that may become a bit troublesome as in some of
> the execution paths where these functions are invoked, are done while
> holding a spinlock with irqs disabled. Invoking pm_runtime_get_sync()
> thus leads to that the irqchip's runtime PM callbacks needs to be
> irqsafe. Another option is to somehow make use the asynchronous API;
> pm_runtime_get() instead.
So that would be ideal, however, I don't think it is that trivial and
hence this is why I have not done this for now.
I don't think that the async callbacks will really help here because if
you call enable_irq() and the chip is runtime suspended, you need to
wait for the chip to resume before you can enable the IRQ. I think that
the disable path would be ok, but not the enable. Plus there could be
some "hot" paths where enable/disable are used and I did not want to
make any assumptions about these.
This may appear ugly, but for something like this, we may need to have a
separate enable/disable API, such as
enable_irq_lazy()/disable_irq_lazy() which could be used to runtime
suspend/resume the chip and must not be used in critical sections.
I was hoping that we could get some initially functionality in place to
allow some basic support for these chips and then enhance it later.
Cheers
Jon
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