* Abhijeet Dharmapurikar ([email protected]) 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.
>
> 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.
Hrm, this strikes me as odd. Is there any way this generic API could
handle the corner-cases without needed the caller to know this ?
[...]
> +/**
> + * 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 !
The comment here seems to imply "be careful when using this extremely
fragile interface", which does not give me the warm safety feeling I
would come to expect from a generic kernel API.
Any ideas on how to improve that ?
Thanks,
Mathieu
> + */
> +int irq_read_line(unsigned int irq)
> +{
> + struct irq_desc *desc = irq_to_desc(irq);
> + unsigned long flags;
> + int val;
> +
> + 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);
> +
> /*
> * Internal function that tells the architecture code whether a
> * particular irq has been exclusively allocated or is available
> --
> 1.7.1
>
> Sent by an employee of the Qualcomm Innovation Center, Inc.
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.
--
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
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