Date:   Mon, 19 Sep 2016 11:16:41 +0300
From:   Mika Westerberg <mika.westerberg@...ux.intel.com>
To:     Marc Zyngier <marc.zyngier@....com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Phidias Chiang <phidias.chiang@...onical.com>,
        Anisse Astier <anisse@...ier.eu>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Yu C Chen <yu.c.chen@...el.com>, linux-gpio@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/3] gpiolib: Make it possible to exclude GPIOs from
 IRQ domain

On Sat, Sep 17, 2016 at 02:13:18PM +0100, Marc Zyngier wrote:
> On Fri, 16 Sep 2016 13:52:41 +0300
> Mika Westerberg <mika.westerberg@...ux.intel.com> wrote:
> 
> Hi Mika,
> 
> > When using GPIO irqchip helpers to setup irqchip for a gpiolib based
> > driver, it is not possible to select which GPIOs to add to the IRQ domain.
> > Instead it just adds all GPIOs which is not always desired. For example
> > there might be GPIOs that for some reason cannot generated normal
> > interrupts at all.
> > 
> > To support this we add a new function gpiochip_irqchip_exclude_irq() that
> > can be used to exclude selected GPIOs from being added to the IRQ domain of
> > the gpiochip in question.
> > 
> > Suggested-by: Linus Walleij <linus.walleij@...aro.org>
> > Signed-off-by: Mika Westerberg <mika.westerberg@...ux.intel.com>
> > ---
> > Thomas, instead of adding flag to struct gpio_chip, I decided to provide an
> > API function that drivers can call. It allocates irq_valid_mask on the fly.
> > 
> > Let me know if you prefer a flag instead.
> > 
> >  Documentation/gpio/driver.txt |  5 +++
> >  drivers/gpio/gpiolib.c        | 72 +++++++++++++++++++++++++++++++++++++++++--
> >  include/linux/gpio/driver.h   |  5 +++
> >  3 files changed, 79 insertions(+), 3 deletions(-)
> > 
> > diff --git a/Documentation/gpio/driver.txt b/Documentation/gpio/driver.txt
> > index 6cb35a78eff4..d12b2ca6fa8e 100644
> > --- a/Documentation/gpio/driver.txt
> > +++ b/Documentation/gpio/driver.txt
> > @@ -256,6 +256,11 @@ associated irqdomain and resource allocation callbacks, the gpiolib has
> >  some helpers that can be enabled by selecting the GPIOLIB_IRQCHIP Kconfig
> >  symbol:
> >  
> > +* gpiochip_irqchip_exclude_irq(): excludes given GPIO from IRQ domain
> > +  created for the gpiochip. This is useful if the GPIO for some reason
> > +  cannot be used as IRQ at all. Note this must be called before
> > +  gpiochip_irqchip_add().
> > +
> >  * gpiochip_irqchip_add(): adds an irqchip to a gpiochip. It will pass
> >    the struct gpio_chip* for the chip to all IRQ callbacks, so the callbacks
> >    need to embed the gpio_chip in its state container and obtain a pointer
> > diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> > index 53ff25ac66d8..31e18dde0ff7 100644
> > --- a/drivers/gpio/gpiolib.c
> > +++ b/drivers/gpio/gpiolib.c
> > @@ -1402,6 +1402,58 @@ static struct gpio_chip *find_chip_by_name(const char *name)
> >   */
> >  
> >  /**
> > + * gpiochip_irqchip_exclude_irq() - Exclude a GPIO from IRQ domain of gpiochip
> > + * @gpiochip: the gpiochip whose IRQ to exclude
> > + * @offset: GPIO number to exclude
> > + *
> > + * Normally all GPIOs in a gpiochip are added to the IRQ domain created for
> > + * that chip. Calling this function allows driver to exclude certain GPIOs
> > + * if for instance the GPIO simply cannot generate interrupts.
> > + *
> > + * This must be called before gpiochip_irqchip_add().
> > + *
> > + * Return: %0 in case of success, negative errno in case of error.
> > + */
> > +int gpiochip_irqchip_exclude_irq(struct gpio_chip *gpiochip,
> > +				 unsigned int offset)
> > +{
> > +	if (WARN_ON_ONCE(gpiochip->irqdomain))
> > +		return -EINVAL;
> > +
> > +	if (offset >= gpiochip->ngpio)
> > +		return -EINVAL;
> > +
> > +	if (!gpiochip->irq_valid_mask) {
> 
> There is a fundamental flaw here, which is the lack of any mutual
> exclusion if you get two simultaneous calls to this function (yes, this
> is unlikely, which means it will happen much earlier than you
> think... ;-).

I thought about this but came to conclusion that it is not possible to
get two simultaneus calls from the same gpio_chip. Or at least I cannot
figure out how that can happen (perhaps I'm missing something). However,
to be on the safe side I think it is better to use a flag instead here
:)

> tglx's solution of adding a flag to your gpiochip gives you that mutual
> exclusion (because the irqdomain doesn't exist yet). The remaining
> question is whether or not flagging the invalid interrupts after the
> irqdomain creation is early enough for you or not. I can't see why not,
> but I know nothing about your HW.

Since gpiochip_irqchip_add() creates both the irqdomain and mapping for
each IRQ, we either need to exclude the invalid IRQs before that
function is called or dispose the mapping in
gpiochip_irqchip_exclude_irq() which can become complex.

How about following (along the lines what Thomas suggested)?

	1. Add flag 'irq_need_valid_mask' to struct gpio_chip
	2. Make gpiochip_add_data() allocate the mask if the above flag is set
	3. Let drivers manipulate that flag directly using set/clear_bit().

> > +		unsigned long *mask;
> > +		int i;
> > +
> > +		mask = kcalloc(BITS_TO_LONGS(gpiochip->ngpio), sizeof(long),
> > +			       GFP_KERNEL);
> > +		if (!mask)
> > +			return -ENOMEM;
> > +
> > +		/* Assume by default all GPIOs are valid */
> > +		for (i = 0; i < gpiochip->ngpio; i++)
> > +			set_bit(i, mask);
> > +
> > +		gpiochip->irq_valid_mask = mask;
> > +	}
> > +
> > +	clear_bit(offset, gpiochip->irq_valid_mask);
> > +	return 0;
> > +}
> > +EXPORT_SYMBOL_GPL(gpiochip_irqchip_exclude_irq);
> > +
> > +static bool gpiochip_irqchip_irq_valid(const struct gpio_chip *gpiochip,
> > +				       unsigned int offset)
> > +{
> > +	/* No mask means all valid */
> > +	if (!gpiochip->irq_valid_mask)
> 
> Could deserves a likely() annotation...

OK, I'll add it.

> > +		return true;
> > +	return test_bit(offset, gpiochip->irq_valid_mask);
> > +}
> > +
> > +/**
> >   * gpiochip_set_chained_irqchip() - sets a chained irqchip to a gpiochip
> >   * @gpiochip: the gpiochip to set the irqchip chain to
> >   * @irqchip: the irqchip to chain to the gpiochip
> > @@ -1442,9 +1494,12 @@ void gpiochip_set_chained_irqchip(struct gpio_chip *gpiochip,
> >  	}
> >  
> >  	/* Set the parent IRQ for all affected IRQs */
> > -	for (offset = 0; offset < gpiochip->ngpio; offset++)
> > +	for (offset = 0; offset < gpiochip->ngpio; offset++) {
> > +		if (!gpiochip_irqchip_irq_valid(gpiochip, offset))
> > +			continue;
> >  		irq_set_parent(irq_find_mapping(gpiochip->irqdomain, offset),
> >  			       parent_irq);
> > +	}
> >  }
> >  EXPORT_SYMBOL_GPL(gpiochip_set_chained_irqchip);
> >  
> > @@ -1551,9 +1606,12 @@ static void gpiochip_irqchip_remove(struct gpio_chip *gpiochip)
> >  
> >  	/* Remove all IRQ mappings and delete the domain */
> >  	if (gpiochip->irqdomain) {
> > -		for (offset = 0; offset < gpiochip->ngpio; offset++)
> > +		for (offset = 0; offset < gpiochip->ngpio; offset++) {
> > +			if (!gpiochip_irqchip_irq_valid(gpiochip, offset))
> > +				continue;
> >  			irq_dispose_mapping(
> >  				irq_find_mapping(gpiochip->irqdomain, offset));
> > +		}
> >  		irq_domain_remove(gpiochip->irqdomain);
> >  	}
> >  
> > @@ -1562,6 +1620,9 @@ static void gpiochip_irqchip_remove(struct gpio_chip *gpiochip)
> >  		gpiochip->irqchip->irq_release_resources = NULL;
> >  		gpiochip->irqchip = NULL;
> >  	}
> > +
> > +	kfree(gpiochip->irq_valid_mask);
> > +	gpiochip->irq_valid_mask = NULL;
> >  }
> >  
> >  /**
> > @@ -1597,6 +1658,7 @@ int _gpiochip_irqchip_add(struct gpio_chip *gpiochip,
> >  			  struct lock_class_key *lock_key)
> >  {
> >  	struct device_node *of_node;
> > +	bool irq_base_set = false;
> >  	unsigned int offset;
> >  	unsigned irq_base = 0;
> >  
> > @@ -1646,13 +1708,17 @@ int _gpiochip_irqchip_add(struct gpio_chip *gpiochip,
> >  	 * necessary to allocate descriptors for all IRQs.
> >  	 */
> >  	for (offset = 0; offset < gpiochip->ngpio; offset++) {
> > +		if (!gpiochip_irqchip_irq_valid(gpiochip, offset))
> > +			continue;
> >  		irq_base = irq_create_mapping(gpiochip->irqdomain, offset);
> > -		if (offset == 0)
> > +		if (!irq_base_set) {
> >  			/*
> >  			 * Store the base into the gpiochip to be used when
> >  			 * unmapping the irqs.
> >  			 */
> >  			gpiochip->irq_base = irq_base;
> > +			irq_base_set = true;
> > +		}
> >  	}
> >  
> >  	acpi_gpiochip_request_interrupts(gpiochip);
> > diff --git a/include/linux/gpio/driver.h b/include/linux/gpio/driver.h
> > index 50882e09289b..c8a4f5511b37 100644
> > --- a/include/linux/gpio/driver.h
> > +++ b/include/linux/gpio/driver.h
> > @@ -112,6 +112,8 @@ enum single_ended_mode {
> >   *	initialization, provided by GPIO driver
> >   * @irq_parent: GPIO IRQ chip parent/bank linux irq number,
> >   *	provided by GPIO driver
> > + * @irq_valid_mask: If not %NULL holds bitmask of GPIOs which are valid to
> > + *	be included in IRQ domain of the chip
> >   * @lock_key: per GPIO IRQ chip lockdep class
> >   *
> >   * A gpio_chip can help platforms abstract various sources of GPIOs so
> > @@ -190,6 +192,7 @@ struct gpio_chip {
> >  	irq_flow_handler_t	irq_handler;
> >  	unsigned int		irq_default_type;
> >  	int			irq_parent;
> > +	unsigned long		*irq_valid_mask;
> >  	struct lock_class_key	*lock_key;
> >  #endif
> >  
> > @@ -260,6 +263,8 @@ int bgpio_init(struct gpio_chip *gc, struct device *dev,
> >  
> >  #ifdef CONFIG_GPIOLIB_IRQCHIP
> >  
> > +int gpiochip_irqchip_exclude_irq(struct gpio_chip *gpiochip,
> > +				 unsigned int offset);
> >  void gpiochip_set_chained_irqchip(struct gpio_chip *gpiochip,
> >  		struct irq_chip *irqchip,
> >  		int parent_irq,
> 
> 
> Thanks,
> 
> 	M.
> -- 
> Jazz is not dead. It just smells funny.

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