linux-kernel - Re: [RFC PATCH] genirq: implement read_irq

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Date:	Fri, 15 Apr 2011 21:11:40 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Abhijeet Dharmapurikar <adharmap@...eaurora.org>
cc:	mathieu.desnoyers@...icios.com, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-kernel@...r.kernel.org, dwalker@...o99.com,
	linux-arm-msm-owner@...r.kernel.org, linux-arm-msm@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	Greg Kroah-Hartman <gregkh@...e.de>
Subject: Re: [RFC PATCH] genirq: implement read_irq_line for interrupt
 lines

On Fri, 15 Apr 2011, Abhijeet Dharmapurikar wrote:

> Some drivers need to know what the status of the interrupt line is.
> This is especially true for drivers that register a handler with
> IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING and in the handler they
> need to know which edge transition it was invoked for.

What's the purpose of this? How is that going to be used?

> The irq_read_line callback in the chip allows the controller to provide
> the real time status of this line. Controllers that can read the status
> of an interrupt line should implement this by doing necessary
> hardware reads and return the logical state of the line.
> 
> Interrupt controllers based on the slow bus architecture should conduct
> the transaction in this callback. The genirq code will call the chip's
> bus lock prior to calling irq_read_line. Obviously since the transaction
> would be completed before returning from irq_read_line it need not do
> any transactions in the bus unlock call.
> 
> Drivers need to be aware whether the interrupt controller is a slow bus
> and call read_irq_line in proper context.
> 
> Signed-off-by: Abhijeet Dharmapurikar <adharmap@...eaurora.org>
> ---
>  include/linux/interrupt.h |    1 +
>  include/linux/irq.h       |    2 ++
>  kernel/irq/manage.c       |   25 +++++++++++++++++++++++++
>  3 files changed, 28 insertions(+), 0 deletions(-)
> 
> diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
> index 59b72ca..0722576 100644
> --- a/include/linux/interrupt.h
> +++ b/include/linux/interrupt.h
> @@ -337,6 +337,7 @@ static inline void enable_irq_lockdep_irqrestore(unsigned int irq, unsigned long
>  
>  /* IRQ wakeup (PM) control: */
>  extern int irq_set_irq_wake(unsigned int irq, unsigned int on);
> +extern int irq_read_line(unsigned int irq);
>  
>  #ifndef CONFIG_GENERIC_HARDIRQS_NO_COMPAT

That hunk does not apply.

>  /* Please do not use: Use the replacement functions instead */
> diff --git a/include/linux/irq.h b/include/linux/irq.h
> index 2a375a7..52198b6 100644
> --- a/include/linux/irq.h
> +++ b/include/linux/irq.h
> @@ -298,6 +298,7 @@ static inline void irqd_clr_chained_irq_inprogress(struct irq_data *d)
>   * @irq_retrigger:	resend an IRQ to the CPU
>   * @irq_set_type:	set the flow type (IRQ_TYPE_LEVEL/etc.) of an IRQ
>   * @irq_set_wake:	enable/disable power-management wake-on of an IRQ
> + * @irq_read_line:	return the current value on the irq line
>   * @irq_bus_lock:	function to lock access to slow bus (i2c) chips
>   * @irq_bus_sync_unlock:function to sync and unlock slow bus (i2c) chips
>   * @irq_cpu_online:	configure an interrupt source for a secondary CPU
> @@ -324,6 +325,7 @@ struct irq_chip {
>  	int		(*irq_retrigger)(struct irq_data *data);
>  	int		(*irq_set_type)(struct irq_data *data, unsigned int flow_type);
>  	int		(*irq_set_wake)(struct irq_data *data, unsigned int on);
> +	int		(*irq_read_line)(struct irq_data *data);
>  
>  	void		(*irq_bus_lock)(struct irq_data *data);
>  	void		(*irq_bus_sync_unlock)(struct irq_data *data);
> diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
> index 12a80fd..6667052 100644
> --- a/kernel/irq/manage.c
> +++ b/kernel/irq/manage.c
> @@ -518,6 +518,31 @@ int irq_set_irq_wake(unsigned int irq, unsigned int on)
>  }
>  EXPORT_SYMBOL(irq_set_irq_wake);
>  
> +/**
> + *	irq_read_line - read the value on an irq line
> + *	@irq: Interrupt number representing a hardware line
> + *
> + *	This function may be called from IRQ context only when
> + *	desc->chip->bus_lock and desc->chip->bus_sync_unlock are NULL !
> + */
> +int irq_read_line(unsigned int irq)
> +{
> +	struct irq_desc *desc = irq_to_desc(irq);
> +	unsigned long flags;
> +	int val;

Please use irq_get_desc_buslock()

> +	if (!desc || !desc->irq_data.chip->irq_read_line)
> +		return -EINVAL;
> +
> +	chip_bus_lock(desc);
> +	raw_spin_lock_irqsave(&desc->lock, flags);
> +	val = desc->irq_data.chip->irq_read_line(&desc->irq_data);
> +	raw_spin_unlock_irqrestore(&desc->lock, flags);
> +	chip_bus_sync_unlock(desc);
> +	return val;
> +}
> +EXPORT_SYMBOL(irq_read_line);

EXPORT_SYMBOL_GPL() please.

Thanks,

	tglx
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