[RFC patch 0/3] Support for irq chips on slow busses (i2c, spi) - V2

[RFC patch 0/3] Support for irq chips on slow busses (i2c, spi) - V2

[Thomas Gleixner]

The support for irq chips on slow busses eg. i2c, spi has been
discussed to great length several times. Most of the details can be
found in this thread: http://lkml.org/lkml/2009/7/21/266

The following patch series is a round up of the various patch snippets
sent out during the discussion and the ideas we agreed on.

This is version 2 of the patch series. The main changes vs. V1
(http://lkml.org/lkml/2009/8/13/348)

 - patch 1/3: Provide a generic primary handler function which just
   	      returns IRQ_WAKE_THREAD as this is all what oneshot
   	      threaded handlers need to avoid useless copies of that
   	      all over the place.

 - patch 2/3: Reverted to the initial idea of conditional locking to
   	      allow drivers to be used for both slowbus and standard
   	      interrupts without any magic in the driver code

 - patch 3/3: To avoid different driver code for nested or separate
   	      thread handling a new function is provided which allows
   	      to mark the interrupt nested. request_threaded_irq()
   	      creates a separate thread only when the flag is not set.

Please have a thorough look and hopefully a test ride on your
favourite slowbus irq chip implementation so we can get this into .32

Thanks,

	tglx

[RFC patch 1/3] genirq: Add oneshot support

[Thomas Gleixner]

[-- Attachment #1: genirq-add-oneshot-support.patch --]
[-- Type: text/plain, Size: 7707 bytes --]

For threaded interrupt handlers we expect the hard interrupt handler
part to mask the interrupt on the originating device. The interrupt
line itself is reenabled after the hard interrupt handler has
executed.

This requires access to the originating device from hard interrupt
context which is not always possible. There are devices which can only
be accessed via a bus (i2c, spi, ...). The bus access requires thread
context. For such devices we need to keep the interrupt line masked
until the threaded handler has executed.

Add a new flag IRQF_ONESHOT which allows drivers to request that the
interrupt is not unmasked after the hard interrupt context handler has
been executed and the thread has been woken. The interrupt line is
unmasked after the thread handler function has been executed.

Note that for now IRQF_ONESHOT cannot be used with IRQF_SHARED to
avoid complex accounting mechanisms.

For oneshot interrupts the primary handler simply returns
IRQ_WAKE_THREAD and does nothing else. A generic implementation
irq_oneshot_primary_handler() is provided to avoid useless copies all
over the place.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Mark Brown <broonie@opensource.wolfsonmicro.com>
Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Cc: Trilok Soni <soni.trilok@gmail.com>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: Brian Swetland <swetland@google.com>
Cc: Joonyoung Shim <jy0922.shim@samsung.com>
Cc: m.szyprowski@samsung.com
Cc: t.fujak@samsung.com
Cc: kyungmin.park@samsung.com,
Cc: David Brownell <david-b@pacbell.net>
Cc: Daniel Ribeiro <drwyrm@gmail.com>
Cc: arve@android.com
Cc: Barry Song <21cnbao@gmail.com>

---
 include/linux/interrupt.h |    6 ++++++
 include/linux/irq.h       |    1 +
 kernel/irq/chip.c         |   31 ++++++++++++++++++++++++++++---
 kernel/irq/manage.c       |   29 +++++++++++++++++++++++++++--
 4 files changed, 62 insertions(+), 5 deletions(-)

Index: linux-2.6-tip/include/linux/interrupt.h
===================================================================
--- linux-2.6-tip.orig/include/linux/interrupt.h
+++ linux-2.6-tip/include/linux/interrupt.h
@@ -49,6 +49,9 @@
  * IRQF_IRQPOLL - Interrupt is used for polling (only the interrupt that is
  *                registered first in an shared interrupt is considered for
  *                performance reasons)
+ * IRQF_ONESHOT - Interrupt is not reenabled after the hardirq handler finished.
+ *                Used by threaded interrupts which need to keep the
+ *                irq line disabled until the threaded handler has been run.
  */
 #define IRQF_DISABLED		0x00000020
 #define IRQF_SAMPLE_RANDOM	0x00000040
@@ -58,6 +61,7 @@
 #define IRQF_PERCPU		0x00000400
 #define IRQF_NOBALANCING	0x00000800
 #define IRQF_IRQPOLL		0x00001000
+#define IRQF_ONESHOT		0x00002000
 
 /*
  * Bits used by threaded handlers:
@@ -286,6 +290,8 @@ static inline int disable_irq_wake(unsig
 	return set_irq_wake(irq, 0);
 }
 
+extern irqreturn_t oneshot_irq_primary_handler(int irq, void *dev_id);
+
 #else /* !CONFIG_GENERIC_HARDIRQS */
 /*
  * NOTE: non-genirq architectures, if they want to support the lock
Index: linux-2.6-tip/include/linux/irq.h
===================================================================
--- linux-2.6-tip.orig/include/linux/irq.h
+++ linux-2.6-tip/include/linux/irq.h
@@ -69,6 +69,7 @@ typedef	void (*irq_flow_handler_t)(unsig
 #define IRQ_MOVE_PCNTXT		0x01000000	/* IRQ migration from process context */
 #define IRQ_AFFINITY_SET	0x02000000	/* IRQ affinity was set from userspace*/
 #define IRQ_SUSPENDED		0x04000000	/* IRQ has gone through suspend sequence */
+#define IRQ_ONESHOT		0x08000000	/* IRQ is not unmasked after hardirq */
 
 #ifdef CONFIG_IRQ_PER_CPU
 # define CHECK_IRQ_PER_CPU(var) ((var) & IRQ_PER_CPU)
Index: linux-2.6-tip/kernel/irq/chip.c
===================================================================
--- linux-2.6-tip.orig/kernel/irq/chip.c
+++ linux-2.6-tip/kernel/irq/chip.c
@@ -300,6 +300,23 @@ static inline void mask_ack_irq(struct i
 }
 
 /**
+ *	irq_oneshot_primary_handler - Handle oneshot interrupt primary handler
+ *	@irq:		the interrupt number
+ *	@dev_id:	cookie to identify the device
+ *
+ *	For oneshot interrupts which keep the interrupt line masked
+ *	until the threaded handler has been executed, the only
+ *	functionality of the primary handler is to return
+ *	IRQ_WAKE_THREAD. This is the generic implementation which
+ *	avoids lots of duplicates all over the place
+ */
+irqreturn_t irq_oneshot_primary_handler(int irq, void *dev_id)
+{
+	return IRQ_WAKE_THREAD;
+}
+EXPORT_SYMBOL_GPL(irq_oneshot_primary_handler);
+
+/**
  *	handle_simple_irq - Simple and software-decoded IRQs.
  *	@irq:	the interrupt number
  *	@desc:	the interrupt description structure for this irq
@@ -382,7 +399,10 @@ handle_level_irq(unsigned int irq, struc
 
 	spin_lock(&desc->lock);
 	desc->status &= ~IRQ_INPROGRESS;
-	if (!(desc->status & IRQ_DISABLED) && desc->chip->unmask)
+
+	if (unlikely(desc->status & IRQ_ONESHOT))
+		desc->status |= IRQ_MASKED;
+	else if (!(desc->status & IRQ_DISABLED) && desc->chip->unmask)
 		desc->chip->unmask(irq);
 out_unlock:
 	spin_unlock(&desc->lock);
@@ -478,8 +498,13 @@ handle_edge_irq(unsigned int irq, struct
 	kstat_incr_irqs_this_cpu(irq, desc);
 
 	/* Start handling the irq */
-	if (desc->chip->ack)
-		desc->chip->ack(irq);
+	if (unlikely(desc->status & IRQ_ONESHOT)) {
+		desc->status |= IRQ_MASKED;
+		mask_ack_irq(desc, irq);
+	} else {
+		if (desc->chip->ack)
+			desc->chip->ack(irq);
+	}
 
 	/* Mark the IRQ currently in progress.*/
 	desc->status |= IRQ_INPROGRESS;
Index: linux-2.6-tip/kernel/irq/manage.c
===================================================================
--- linux-2.6-tip.orig/kernel/irq/manage.c
+++ linux-2.6-tip/kernel/irq/manage.c
@@ -444,6 +444,21 @@ static int irq_wait_for_interrupt(struct
 }
 
 /*
+ * Oneshot interrupts keep the irq line masked until the threaded
+ * handler finished. unmask if the interrupt has not been disabled and
+ * is marked MASKED.
+ */
+static void irq_finalize_oneshot(unsigned int irq, struct irq_desc *desc)
+{
+	spin_lock_irq(&desc->lock);
+	if (!(desc->status & IRQ_DISABLED) && (desc->status & IRQ_MASKED)) {
+		desc->status &= ~IRQ_MASKED;
+		desc->chip->unmask(irq);
+	}
+	spin_unlock_irq(&desc->lock);
+}
+
+/*
  * Interrupt handler thread
  */
 static int irq_thread(void *data)
@@ -451,7 +466,7 @@ static int irq_thread(void *data)
 	struct sched_param param = { .sched_priority = MAX_USER_RT_PRIO/2, };
 	struct irqaction *action = data;
 	struct irq_desc *desc = irq_to_desc(action->irq);
-	int wake;
+	int wake, oneshot = desc->status & IRQ_ONESHOT;
 
 	sched_setscheduler(current, SCHED_FIFO, &param);
 	current->irqaction = action;
@@ -475,6 +490,9 @@ static int irq_thread(void *data)
 			spin_unlock_irq(&desc->lock);
 
 			action->thread_fn(action->irq, action->dev_id);
+
+			if (oneshot)
+				irq_finalize_oneshot(action->irq, desc);
 		}
 
 		wake = atomic_dec_and_test(&desc->threads_active);
@@ -547,6 +565,10 @@ __setup_irq(unsigned int irq, struct irq
 		rand_initialize_irq(irq);
 	}
 
+	/* Oneshot interrupts are not allowed with shared */
+	if ((new->flags & IRQF_ONESHOT) && (new->flags & IRQF_SHARED))
+		return -EINVAL;
+
 	/*
 	 * Threaded handler ?
 	 */
@@ -620,9 +642,12 @@ __setup_irq(unsigned int irq, struct irq
 			desc->status |= IRQ_PER_CPU;
 #endif
 
-		desc->status &= ~(IRQ_AUTODETECT | IRQ_WAITING |
+		desc->status &= ~(IRQ_AUTODETECT | IRQ_WAITING | IRQ_ONESHOT |
 				  IRQ_INPROGRESS | IRQ_SPURIOUS_DISABLED);
 
+		if (new->flags & IRQF_ONESHOT)
+			desc->status |= IRQ_ONESHOT;
+
 		if (!(desc->status & IRQ_NOAUTOEN)) {
 			desc->depth = 0;
 			desc->status &= ~IRQ_DISABLED;

Re: [RFC patch 1/3] genirq: Add oneshot support

[Dmitry Torokhov]

Hi Thomas,

On Sat, Aug 15, 2009 at 05:48:33PM -0000, Thomas Gleixner wrote:
>  
>  /**
> + *	irq_oneshot_primary_handler - Handle oneshot interrupt primary handler
> + *	@irq:		the interrupt number
> + *	@dev_id:	cookie to identify the device
> + *
> + *	For oneshot interrupts which keep the interrupt line masked
> + *	until the threaded handler has been executed, the only
> + *	functionality of the primary handler is to return
> + *	IRQ_WAKE_THREAD. This is the generic implementation which
> + *	avoids lots of duplicates all over the place
> + */
> +irqreturn_t irq_oneshot_primary_handler(int irq, void *dev_id)
> +{
> +	return IRQ_WAKE_THREAD;
> +}
> +EXPORT_SYMBOL_GPL(irq_oneshot_primary_handler);

This kind of handler is useful not only for users of oneshot interrupts
but also other drivers using threaded IRQs. So maybe we should rename it
to default_threaded_irq_handler() and instead of exporting it simply
have it installed automatically when driver requests NULL in place of
IRQ handler in request_threaded_irq()?

Also, if IRQF_ONESHOT definition would make into mainline sooner than
later that would be great - then I'd be able to put all the drivers that
will end up using it into my next branch and not be concerned of
breaking linux-next.

-- 
Dmitry

Re: [RFC patch 1/3] genirq: Add oneshot support

[Thomas Gleixner]

Dmitry,

On Sat, 15 Aug 2009, Dmitry Torokhov wrote:
> Hi Thomas,
> 
> On Sat, Aug 15, 2009 at 05:48:33PM -0000, Thomas Gleixner wrote:
> >  
> >  /**
> > + *	irq_oneshot_primary_handler - Handle oneshot interrupt primary handler
> > + *	@irq:		the interrupt number
> > + *	@dev_id:	cookie to identify the device
> > + *
> > + *	For oneshot interrupts which keep the interrupt line masked
> > + *	until the threaded handler has been executed, the only
> > + *	functionality of the primary handler is to return
> > + *	IRQ_WAKE_THREAD. This is the generic implementation which
> > + *	avoids lots of duplicates all over the place
> > + */
> > +irqreturn_t irq_oneshot_primary_handler(int irq, void *dev_id)
> > +{
> > +	return IRQ_WAKE_THREAD;
> > +}
> > +EXPORT_SYMBOL_GPL(irq_oneshot_primary_handler);
> 
> This kind of handler is useful not only for users of oneshot interrupts
> but also other drivers using threaded IRQs. So maybe we should rename it
> to default_threaded_irq_handler() and instead of exporting it simply
> have it installed automatically when driver requests NULL in place of
> IRQ handler in request_threaded_irq()?

Good point. If handler == NULL and thread_fn != NULL. That's
reasonable. Will rework.
 
> Also, if IRQF_ONESHOT definition would make into mainline sooner than
> later that would be great - then I'd be able to put all the drivers that
> will end up using it into my next branch and not be concerned of
> breaking linux-next.

Hmm, the ONESHOT definition alone won't give you the testing you
want. If all involved folks agree on the patch series I can commit it
into a standalone branch which can be pulled into the development
branches of interested driver maintainers. Git will deal with that
just fine.

@Andrew: any opinion on that ?

Thanks,

	tglx

[RFC patch 2/3] genirq: Add buslock support

[Thomas Gleixner]

[-- Attachment #1: genirq-add-buslock-support.patch --]
[-- Type: text/plain, Size: 7845 bytes --]

Some interrupt chips are connected to a "slow" bus (i2c, spi ...). The
bus access needs to sleep and therefor cannot be called in atomic
contexts.

Some of the generic interrupt management functions like disable_irq(),
enable_irq() ... call interrupt chip functions with the irq_desc->lock
held and interrupts disabled. This does not work for such devices.

Provide a separate synchronization mechanism for such interrupt
chips. The irq_chip structure is extended by two optional functions
(bus_lock and bus_sync_and_unlock).

The idea is to serialize the bus access for those operations in the
core code so that drivers which are behind that bus operated interrupt
controller do not have to worry about it and just can use the normal
interfaces. To achieve this we add two function pointers to the
irq_chip: bus_lock and bus_sync_unlock.

bus_lock() is called to serialize access to the interrupt controller
bus.

Now the core code can issue chip->mask/unmask ... commands without
changing the fast path code at all. The chip implementation merily
stores that information in a chip private data structure and
returns. No bus interaction as these functions are called from atomic
context.

After that bus_sync_unlock() is called outside the atomic context. Now
the chip implementation issues the bus commands, waits for completion
and unlocks the interrupt controller bus.

The irq_chip implementation as pseudo code:

struct irq_chip_data {
       struct mutex   mutex;
       unsigned int   irq_offset;
       unsigned long  mask;
       unsigned long  mask_status;
}

static void bus_lock(unsigned int irq)
{
        struct irq_chip_data *data = get_irq_desc_chip_data(irq);

        mutex_lock(&data->mutex);
}

static void mask(unsigned int irq)
{
        struct irq_chip_data *data = get_irq_desc_chip_data(irq);

        irq -= data->irq_offset;
        data->mask |= (1 << irq);
}

static void unmask(unsigned int irq)
{
        struct irq_chip_data *data = get_irq_desc_chip_data(irq);

        irq -= data->irq_offset;
        data->mask &= ~(1 << irq);
}

static void bus_sync_unlock(unsigned int irq)
{
        struct irq_chip_data *data = get_irq_desc_chip_data(irq);

        if (data->mask != data->mask_status) {
                do_bus_magic_to_set_mask(data->mask);
                data->mask_status = data->mask;
        }
        mutex_unlock(&data->mutex);
}

The device drivers can use request_threaded_irq, free_irq, disable_irq
and enable_irq as usual with the only restriction that the calls need
to come from non atomic context.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Mark Brown <broonie@opensource.wolfsonmicro.com>
Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Cc: Trilok Soni <soni.trilok@gmail.com>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: Brian Swetland <swetland@google.com>
Cc: Joonyoung Shim <jy0922.shim@samsung.com>
Cc: m.szyprowski@samsung.com
Cc: t.fujak@samsung.com
Cc: kyungmin.park@samsung.com,
Cc: David Brownell <david-b@pacbell.net>
Cc: Daniel Ribeiro <drwyrm@gmail.com>
Cc: arve@android.com
Cc: Barry Song <21cnbao@gmail.com>

---
 include/linux/irq.h    |    6 ++++++
 kernel/irq/chip.c      |    2 ++
 kernel/irq/internals.h |   13 +++++++++++++
 kernel/irq/manage.c    |   19 ++++++++++++++++++-
 4 files changed, 39 insertions(+), 1 deletion(-)

Index: linux-2.6-tip/include/linux/irq.h
===================================================================
--- linux-2.6-tip.orig/include/linux/irq.h
+++ linux-2.6-tip/include/linux/irq.h
@@ -101,6 +101,9 @@ struct msi_desc;
  * @set_type:		set the flow type (IRQ_TYPE_LEVEL/etc.) of an IRQ
  * @set_wake:		enable/disable power-management wake-on of an IRQ
  *
+ * @bus_lock:		function to lock access to slow bus (i2c) chips
+ * @bus_sync_unlock:	function to sync and unlock slow bus (i2c) chips
+ *
  * @release:		release function solely used by UML
  * @typename:		obsoleted by name, kept as migration helper
  */
@@ -124,6 +127,9 @@ struct irq_chip {
 	int		(*set_type)(unsigned int irq, unsigned int flow_type);
 	int		(*set_wake)(unsigned int irq, unsigned int on);
 
+	void		(*bus_lock)(unsigned int irq);
+	void		(*bus_sync_unlock)(unsigned int irq);
+
 	/* Currently used only by UML, might disappear one day.*/
 #ifdef CONFIG_IRQ_RELEASE_METHOD
 	void		(*release)(unsigned int irq, void *dev_id);
Index: linux-2.6-tip/kernel/irq/chip.c
===================================================================
--- linux-2.6-tip.orig/kernel/irq/chip.c
+++ linux-2.6-tip/kernel/irq/chip.c
@@ -597,6 +597,7 @@ __set_irq_handler(unsigned int irq, irq_
 		desc->chip = &dummy_irq_chip;
 	}
 
+	chip_bus_lock(irq, desc);
 	spin_lock_irqsave(&desc->lock, flags);
 
 	/* Uninstall? */
@@ -616,6 +617,7 @@ __set_irq_handler(unsigned int irq, irq_
 		desc->chip->startup(irq);
 	}
 	spin_unlock_irqrestore(&desc->lock, flags);
+	chip_bus_sync_unlock(irq, desc);
 }
 EXPORT_SYMBOL_GPL(__set_irq_handler);
 
Index: linux-2.6-tip/kernel/irq/internals.h
===================================================================
--- linux-2.6-tip.orig/kernel/irq/internals.h
+++ linux-2.6-tip/kernel/irq/internals.h
@@ -45,6 +45,19 @@ extern int irq_select_affinity_usr(unsig
 extern void
 irq_set_thread_affinity(struct irq_desc *desc, const struct cpumask *cpumask);
 
+/* Inline functions for support of irq chips on slow busses */
+static inline void chip_bus_lock(unsigned int irq, struct irq_desc *desc)
+{
+	if (unlikely(desc->chip->bus_lock))
+		desc->chip->bus_lock(irq);
+}
+
+static inline void chip_bus_sync_unlock(unsigned int irq, struct irq_desc *desc)
+{
+	if (unlikely(desc->chip->bus_sync_unlock))
+		desc->chip->bus_sync_unlock(irq);
+}
+
 /*
  * Debugging printout:
  */
Index: linux-2.6-tip/kernel/irq/manage.c
===================================================================
--- linux-2.6-tip.orig/kernel/irq/manage.c
+++ linux-2.6-tip/kernel/irq/manage.c
@@ -222,9 +222,11 @@ void disable_irq_nosync(unsigned int irq
 	if (!desc)
 		return;
 
+	chip_bus_lock(irq, desc);
 	spin_lock_irqsave(&desc->lock, flags);
 	__disable_irq(desc, irq, false);
 	spin_unlock_irqrestore(&desc->lock, flags);
+	chip_bus_sync_unlock(irq, desc);
 }
 EXPORT_SYMBOL(disable_irq_nosync);
 
@@ -286,7 +288,8 @@ void __enable_irq(struct irq_desc *desc,
  *	matches the last disable, processing of interrupts on this
  *	IRQ line is re-enabled.
  *
- *	This function may be called from IRQ context.
+ *	This function may be called from IRQ context only when
+ *	desc->chip->bus_lock and desc->chip->bus_sync_unlock are NULL !
  */
 void enable_irq(unsigned int irq)
 {
@@ -296,9 +299,11 @@ void enable_irq(unsigned int irq)
 	if (!desc)
 		return;
 
+	chip_bus_lock(irq, desc);
 	spin_lock_irqsave(&desc->lock, flags);
 	__enable_irq(desc, irq, false);
 	spin_unlock_irqrestore(&desc->lock, flags);
+	chip_bus_sync_unlock(irq, desc);
 }
 EXPORT_SYMBOL(enable_irq);
 
@@ -450,12 +455,14 @@ static int irq_wait_for_interrupt(struct
  */
 static void irq_finalize_oneshot(unsigned int irq, struct irq_desc *desc)
 {
+	chip_bus_lock(irq, desc);
 	spin_lock_irq(&desc->lock);
 	if (!(desc->status & IRQ_DISABLED) && (desc->status & IRQ_MASKED)) {
 		desc->status &= ~IRQ_MASKED;
 		desc->chip->unmask(irq);
 	}
 	spin_unlock_irq(&desc->lock);
+	chip_bus_sync_unlock(irq, desc);
 }
 
 /*
@@ -854,7 +861,14 @@ EXPORT_SYMBOL_GPL(remove_irq);
  */
 void free_irq(unsigned int irq, void *dev_id)
 {
+	struct irq_desc *desc = irq_to_desc(irq);
+
+	if (!desc)
+		return;
+
+	chip_bus_lock(irq, desc);
 	kfree(__free_irq(irq, dev_id));
+	chip_bus_sync_unlock(irq, desc);
 }
 EXPORT_SYMBOL(free_irq);
 
@@ -955,7 +969,10 @@ int request_threaded_irq(unsigned int ir
 	action->name = devname;
 	action->dev_id = dev_id;
 
+	chip_bus_lock(irq, desc);
 	retval = __setup_irq(irq, desc, action);
+	chip_bus_sync_unlock(irq, desc);
+
 	if (retval)
 		kfree(action);
 

[RFC patch 3/3] genirq: Support nested threaded irq handling

[Thomas Gleixner]

[-- Attachment #1: genirq-support-nested-threaded-irq-handling.patch --]
[-- Type: text/plain, Size: 7103 bytes --]

Interrupt chips which are behind a slow bus (i2c, spi ...) and
demultiplex other interrupt sources need to run their interrupt
handler in a thread. 

The demultiplexed interrupt handlers need to run in thread context as
well and need to finish before the demux handler thread can reenable
the interrupt line. So the easiest way is to run the sub device
handlers in the context of the demultiplexing handler thread.

To avoid that a separate thread is created for the subdevices the
function set_nested_irq_thread() is provided which sets the
IRQ_NESTED_THREAD flag in the interrupt descriptor.

A driver which calls request_threaded_irq() must not be aware of the
fact that the threaded handler is called in the context of the
demultiplexing handler thread. The setup code checks the
IRQ_NESTED_THREAD flag which was set from the irq chip setup code and
does not setup a separate thread for the interrupt. The primary
function which is provided by the device driver is replaced by an
internal dummy function which warns when it is called.

For the demultiplexing handler a helper function handle_nested_irq()
is provided which calls the demux interrupt thread function in the
context of the caller and does the proper interrupt accounting and
takes the interrupt disabled status of the demultiplexed subdevice
into account.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Mark Brown <broonie@opensource.wolfsonmicro.com>
Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Cc: Trilok Soni <soni.trilok@gmail.com>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: Brian Swetland <swetland@google.com>
Cc: Joonyoung Shim <jy0922.shim@samsung.com>
Cc: m.szyprowski@samsung.com
Cc: t.fujak@samsung.com
Cc: kyungmin.park@samsung.com,
Cc: David Brownell <david-b@pacbell.net>
Cc: Daniel Ribeiro <drwyrm@gmail.com>
Cc: arve@android.com
Cc: Barry Song <21cnbao@gmail.com>

---
 include/linux/irq.h    |    3 ++
 kernel/irq/chip.c      |   73 +++++++++++++++++++++++++++++++++++++++++++++++++
 kernel/irq/internals.h |    2 +
 kernel/irq/manage.c    |   24 ++++++++++++++--
 4 files changed, 99 insertions(+), 3 deletions(-)

Index: linux-2.6-tip/include/linux/irq.h
===================================================================
--- linux-2.6-tip.orig/include/linux/irq.h
+++ linux-2.6-tip/include/linux/irq.h
@@ -70,6 +70,7 @@ typedef	void (*irq_flow_handler_t)(unsig
 #define IRQ_AFFINITY_SET	0x02000000	/* IRQ affinity was set from userspace*/
 #define IRQ_SUSPENDED		0x04000000	/* IRQ has gone through suspend sequence */
 #define IRQ_ONESHOT		0x08000000	/* IRQ is not unmasked after hardirq */
+#define IRQ_NESTED_THREAD	0x10000000	/* IRQ is nested into another, no own handler thread */
 
 #ifdef CONFIG_IRQ_PER_CPU
 # define CHECK_IRQ_PER_CPU(var) ((var) & IRQ_PER_CPU)
@@ -379,6 +380,8 @@ set_irq_chained_handler(unsigned int irq
 	__set_irq_handler(irq, handle, 1, NULL);
 }
 
+extern void set_irq_nested_thread(unsigned int irq, int nest);
+
 extern void set_irq_noprobe(unsigned int irq);
 extern void set_irq_probe(unsigned int irq);
 
Index: linux-2.6-tip/kernel/irq/chip.c
===================================================================
--- linux-2.6-tip.orig/kernel/irq/chip.c
+++ linux-2.6-tip/kernel/irq/chip.c
@@ -222,6 +222,34 @@ int set_irq_chip_data(unsigned int irq, 
 }
 EXPORT_SYMBOL(set_irq_chip_data);
 
+/**
+ *	set_irq_nested_thread - Set/Reset the IRQ_NESTED_THREAD flag of an irq
+ *
+ *	@irq:	Interrupt number
+ *	@nest:	0 to clear / 1 to set the IRQ_NESTED_THREAD flag
+ *
+ *	The IRQ_NESTED_THREAD flag indicates that on
+ *	request_threaded_irq() no separate interrupt thread should be
+ *	created for the irq as the handler are called nested in the
+ *	context of a demultiplexing interrupt handler thread.
+ */
+void set_irq_nested_thread(unsigned int irq, int nest)
+{
+	struct irq_desc *desc = irq_to_desc(irq);
+	unsigned long flags;
+
+	if (!desc)
+		return;
+
+	spin_lock_irqsave(&desc->lock, flags);
+	if (nest)
+		desc->status |= IRQ_NESTED_THREAD;
+	else
+		desc->status &= ~IRQ_NESTED_THREAD;
+	spin_unlock_irqrestore(&desc->lock, flags);
+}
+EXPORT_SYMBOL_GPL(set_irq_nested_thread);
+
 /*
  * default enable function
  */
@@ -316,6 +344,51 @@ irqreturn_t irq_oneshot_primary_handler(
 }
 EXPORT_SYMBOL_GPL(irq_oneshot_primary_handler);
 
+/*
+ *	handle_nested_irq - Handle a nested irq from a irq thread
+ *	@irq:	the interrupt number
+ *
+ *	Handle interrupts which are nested into a threaded interrupt
+ *	handler. The handler function is called inside the calling
+ *	threads context.
+ */
+void handle_nested_irq(unsigned int irq)
+{
+	struct irq_desc *desc = irq_to_desc(irq);
+	struct irqaction *action;
+	irqreturn_t action_ret;
+
+	might_sleep();
+
+	spin_lock_irq(&desc->lock);
+
+	kstat_incr_irqs_this_cpu(irq, desc);
+
+	action = desc->action;
+	if (unlikely(!action || (desc->status & IRQ_DISABLED)))
+		goto out_unlock;
+
+	desc->status |= IRQ_INPROGRESS;
+	spin_unlock_irq(&desc->lock);
+
+	action_ret = action->thread_fn(action->irq, action->dev_id);
+	if (!noirqdebug)
+		note_interrupt(irq, desc, action_ret);
+
+	spin_lock_irq(&desc->lock);
+	desc->status &= ~IRQ_INPROGRESS;
+
+out_unlock:
+	spin_unlock_irq(&desc->lock);
+}
+EXPORT_SYMBOL_GPL(handle_nested_irq);
+
+irqreturn_t handle_nested_irq_primary(int irq, void *dev_id)
+{
+	WARN(1, "Primary handler called for nested irq %d\n", irq);
+	return IRQ_NONE;
+}
+
 /**
  *	handle_simple_irq - Simple and software-decoded IRQs.
  *	@irq:	the interrupt number
Index: linux-2.6-tip/kernel/irq/internals.h
===================================================================
--- linux-2.6-tip.orig/kernel/irq/internals.h
+++ linux-2.6-tip/kernel/irq/internals.h
@@ -58,6 +58,8 @@ static inline void chip_bus_sync_unlock(
 		desc->chip->bus_sync_unlock(irq);
 }
 
+extern irqreturn_t handle_nested_irq_primary(int irq, void *dev_id);
+
 /*
  * Debugging printout:
  */
Index: linux-2.6-tip/kernel/irq/manage.c
===================================================================
--- linux-2.6-tip.orig/kernel/irq/manage.c
+++ linux-2.6-tip/kernel/irq/manage.c
@@ -547,7 +547,7 @@ __setup_irq(unsigned int irq, struct irq
 	struct irqaction *old, **old_ptr;
 	const char *old_name = NULL;
 	unsigned long flags;
-	int shared = 0;
+	int nested, shared = 0;
 	int ret;
 
 	if (!desc)
@@ -577,9 +577,27 @@ __setup_irq(unsigned int irq, struct irq
 		return -EINVAL;
 
 	/*
-	 * Threaded handler ?
+	 * Check whether the interrupt nests into another interrupt
+	 * thread.
 	 */
-	if (new->thread_fn) {
+	nested = desc->status & IRQ_NESTED_THREAD;
+	if (nested) {
+		if (!new->thread_fn)
+			return -EINVAL;
+		/*
+		 * Replace the primary handler which was provided from
+		 * the driver for non nested interrupt handling by the
+		 * dummy function which warns when called.
+		 */
+		new->handler = handle_nested_irq_primary;
+	}
+
+	/*
+	 * Create a handler thread when a thread function is supplied
+	 * and the interrupt does not nest into another interrupt
+	 * thread.
+	 */
+	if (new->thread_fn && !nested) {
 		struct task_struct *t;
 
 		t = kthread_create(irq_thread, new, "irq/%d-%s", irq,

Re: [RFC patch 0/3] Support for irq chips on slow busses (i2c, spi) - V2

[Pavel Machek]

Hi!

> The support for irq chips on slow busses eg. i2c, spi has been
> discussed to great length several times. Most of the details can be
> found in this thread: http://lkml.org/lkml/2009/7/21/266
> 
> The following patch series is a round up of the various patch snippets
> sent out during the discussion and the ideas we agreed on.
> 
> This is version 2 of the patch series. The main changes vs. V1
> (http://lkml.org/lkml/2009/8/13/348)
> 
>  - patch 1/3: Provide a generic primary handler function which just
>    	      returns IRQ_WAKE_THREAD as this is all what oneshot
>    	      threaded handlers need to avoid useless copies of that
>    	      all over the place.
> 
>  - patch 2/3: Reverted to the initial idea of conditional locking to
>    	      allow drivers to be used for both slowbus and standard
>    	      interrupts without any magic in the driver code
> 
>  - patch 3/3: To avoid different driver code for nested or separate
>    	      thread handling a new function is provided which allows
>    	      to mark the interrupt nested. request_threaded_irq()
>    	      creates a separate thread only when the flag is not set.
> 
> Please have a thorough look and hopefully a test ride on your
> favourite slowbus irq chip implementation so we can get this into .32

FWIW, it looks ok to me.
					Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

Re: [RFC patch 0/3] Support for irq chips on slow busses (i2c, spi) - V2

[Mark Brown]

On Sat, Aug 15, 2009 at 05:48:26PM -0000, Thomas Gleixner wrote:

> Please have a thorough look and hopefully a test ride on your
> favourite slowbus irq chip implementation so we can get this into .32

I've given this a spin with such a chip and it seems to be working OK
for me, though I've only done very light testing.  The only issue I ran
into was a lack of a prototype for handle_nested_irq() - I've sent a
patch for that.

Thanks a lot for working on this!

[RFC patch 0/3] Support for irq chips on slow busses (i2c, spi)

[Thomas Gleixner]

The support for irq chips on slow busses eg. i2c, spi has been
discussed to great length several times. Most of the details can be
found in this thread: http://lkml.org/lkml/2009/7/21/266

The following patch series is a round up of the various patch snippets
sent out during the discussion and the ideas we agreed on.

There are some subtle differences to the initial test patches:

1) Instead of using a separate flow handler we allow to request the
one shot feature with a flag on request_irq and integrate the oneshot
feature into the existing level/edge handlers.

2) Instead of conditional locking which makes the patch smaller but
hides the already known fact that a device sits behind a slow irq chip
I implemented a set of separate management functions (see patch
2/3). The initial idea with the conditional locking can be found here:
http://lkml.org/lkml/2009/7/22/163

3) patch 3/3 implements a helper function which allows the
demultiplexing thread to call the demux handlers in its own thread
context with out creating a separate thread for each subdevice
interrupt. The device driver needs to request the interrupt via
request_nested_slowbus_irq() to prevent the creation of the extra
thread.

Please have a thorough look and hopefully a test ride on your
favourite slowbus irq chip implementation so we can get this into .32

Thanks,

	tglx

[RFC patch 3/3] genirq: Support nested threaded irq handling

[Thomas Gleixner]

[-- Attachment #1: genirq-support-nested-threaded-irq-handling.patch --]
[-- Type: text/plain, Size: 5881 bytes --]

Interrupt chips which are behind a slow bus (i2c, spi ...) and
demultiplex other interrupt sources need to run their interrupt
handler in a thread. 

The demultiplexed interrupt handlers need to run in thread context as
well and need to finish before the demux handler thread can reenable
the interrupt line. So instead of creating separate threads which need
to synchronize with the demux handler thread we provide a function
which calls the interrupt thread function of the sub device in the
context of the demux handler thread.

To avoid that a separate thread is created for the subdevices the
function request_nested_slowbus_irq() is provided which sets a dummy
handler for the primary handler which should never be called. A flag
prevents the creation of the separate handler thread in __setup_irq().

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

---
 include/linux/interrupt.h |    9 +++++++++
 kernel/irq/chip.c         |   44 ++++++++++++++++++++++++++++++++++++++++++++
 kernel/irq/internals.h    |    2 ++
 kernel/irq/manage.c       |   28 +++++++++++++++++++++++++++-
 4 files changed, 82 insertions(+), 1 deletion(-)

Index: linux-2.6-tip/include/linux/interrupt.h
===================================================================
--- linux-2.6-tip.orig/include/linux/interrupt.h
+++ linux-2.6-tip/include/linux/interrupt.h
@@ -52,6 +52,9 @@
  * IRQF_ONESHOT - Interrupt is not reenabled after the hardirq handler finished.
  *                Used by threaded interrupts which need to keep the
  *                irq line disabled until the threaded handler has been run.
+ * IRQF_NESTED -  Interrupt is nested into another threaded interrupt. Handler
+ *		  is called in the parent interrupt thread context
+ *
  */
 #define IRQF_DISABLED		0x00000020
 #define IRQF_SAMPLE_RANDOM	0x00000040
@@ -62,6 +65,7 @@
 #define IRQF_NOBALANCING	0x00000800
 #define IRQF_IRQPOLL		0x00001000
 #define IRQF_ONESHOT		0x00002000
+#define IRQF_NESTED		0x00004000
 
 /*
  * Bits used by threaded handlers:
@@ -125,6 +129,11 @@ request_irq(unsigned int irq, irq_handle
 	return request_threaded_irq(irq, handler, NULL, flags, name, dev);
 }
 
+extern int __must_check
+request_nested_slowbus_irq(unsigned int irq, irq_handler_t thread_fn,
+			   unsigned long irqflags, const char *devname,
+			   void *dev_id);
+
 extern void exit_irq_thread(void);
 #else
 
Index: linux-2.6-tip/kernel/irq/chip.c
===================================================================
--- linux-2.6-tip.orig/kernel/irq/chip.c
+++ linux-2.6-tip/kernel/irq/chip.c
@@ -300,6 +300,50 @@ static inline void mask_ack_irq(struct i
 }
 
 /**
+ *	handle_nested_irq - Handle a nested irq from a irq thread
+ *	@irq:	the interrupt number
+ *
+ *	Handle interrupts which are nested into a threaded interrupt
+ *	handler. The handler function is called inside the calling
+ *	threads context.
+ */
+void handle_nested_irq(unsigned int irq)
+{
+	struct irq_desc *desc = irq_to_desc(irq);
+	struct irqaction *action;
+	irqreturn_t action_ret;
+
+	might_sleep();
+
+	spin_lock_irq(&desc->lock);
+
+	kstat_incr_irqs_this_cpu(irq, desc);
+
+	action = desc->action;
+	if (unlikely(!action || (desc->status & IRQ_DISABLED)))
+		goto out_unlock;
+
+	desc->status |= IRQ_INPROGRESS;
+	spin_unlock_irq(&desc->lock);
+
+	action_ret = action->thread_fn(action->irq, action->dev_id);
+	if (!noirqdebug)
+		note_interrupt(irq, desc, action_ret);
+
+	spin_lock_irq(&desc->lock);
+	desc->status &= ~IRQ_INPROGRESS;
+
+out_unlock:
+	spin_unlock_irq(&desc->lock);
+}
+
+irqreturn_t handle_nested_irq_primary(int irq, void *dev_id)
+{
+	WARN(1, "Primary handler called for nested irq %d\n", irq);
+	return IRQ_NONE;
+}
+
+/**
  *	handle_simple_irq - Simple and software-decoded IRQs.
  *	@irq:	the interrupt number
  *	@desc:	the interrupt description structure for this irq
Index: linux-2.6-tip/kernel/irq/internals.h
===================================================================
--- linux-2.6-tip.orig/kernel/irq/internals.h
+++ linux-2.6-tip/kernel/irq/internals.h
@@ -45,6 +45,8 @@ extern int irq_select_affinity_usr(unsig
 extern void
 irq_set_thread_affinity(struct irq_desc *desc, const struct cpumask *cpumask);
 
+extern irqreturn_t handle_nested_irq_primary(int irq, void *dev_id);
+
 /*
  * Debugging printout:
  */
Index: linux-2.6-tip/kernel/irq/manage.c
===================================================================
--- linux-2.6-tip.orig/kernel/irq/manage.c
+++ linux-2.6-tip/kernel/irq/manage.c
@@ -625,7 +625,7 @@ __setup_irq(unsigned int irq, struct irq
 	/*
 	 * Threaded handler ?
 	 */
-	if (new->thread_fn) {
+	if (new->thread_fn && !(new->flags & IRQF_NESTED)) {
 		struct task_struct *t;
 
 		t = kthread_create(irq_thread, new, "irq/%d-%s", irq,
@@ -1095,3 +1095,29 @@ int request_slowbus_threaded_irq(unsigne
 	return res;
 }
 EXPORT_SYMBOL(request_slowbus_threaded_irq);
+
+/**
+ *	request_nested_slowbus_irq - allocate an interrupt line for a nested irq
+ *	@irq: Interrupt line to allocate
+ *	@thread_fn: Function called from the irq handler thread
+ *	@irqflags: Interrupt type flags
+ *	@devname: An ascii name for the claiming device
+ *	@dev_id: A cookie passed back to the handler function
+ *
+ *	This function is used for interrupts which nest into another
+ *	threaded interrupt handler, e.g. subdevice interrupts of an
+ *	interrupt controller which is connected via i2c/spi or other
+ *	slow path mechanisms. The thread_fn is called from the
+ *	demultiplexing interrupt thread via handle_nested_irq().
+ */
+int request_nested_slowbus_irq(unsigned int irq, irq_handler_t thread_fn,
+			       unsigned long irqflags, const char *devname,
+			       void *dev_id)
+{
+	irqflags |= IRQF_NESTED;
+
+	return request_threaded_slowbus_irq(irq, handle_nested_irq_primary,
+					    thread_fn, irqflags, devname,
+					    dev_id);
+}
+EXPORT_SYMBOL(request_nested_slowbus_irq);