linux-kernel - Re: [PATCH v2 1/5] irqchip: add dumb demultiplexer implementation

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Date:	Wed, 14 Jan 2015 15:43:29 +0100
From:	Nicolas Ferre <nicolas.ferre@...el.com>
To:	Boris Brezillon <boris.brezillon@...e-electrons.com>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	Jason Cooper <jason@...edaemon.net>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>, Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>, <devicetree@...r.kernel.org>
Subject: Re: [PATCH v2 1/5] irqchip: add dumb demultiplexer implementation

Le 14/01/2015 15:03, Boris Brezillon a écrit :
> On Wed, 14 Jan 2015 14:36:42 +0100
> Nicolas Ferre <nicolas.ferre@...el.com> wrote:
> 
>> Le 13/01/2015 19:46, Boris Brezillon a écrit :
>>> Some interrupt controllers are multiplexing several peripheral IRQs on
>>> a single interrupt line.
>>> While this is not a problem for most IRQs (as long as all peripherals
>>> request the interrupt with IRQF_SHARED flag set), multiplexing timers and
>>> other type of peripherals will generate a WARNING (mixing IRQF_NO_SUSPEND
>>> and !IRQF_NO_SUSPEND is prohibited).
>>>
>>> Create a dumb irq demultiplexer which simply forwards interrupts to all
>>> peripherals (exactly what's happening with IRQ_SHARED) but keep a unique
>>> irq number for each peripheral, thus preventing the IRQF_NO_SUSPEND
>>> and !IRQF_NO_SUSPEND mix on a given interrupt.
>>>
>>> Signed-off-by: Boris Brezillon <boris.brezillon@...e-electrons.com>
>>> ---
>>>  drivers/irqchip/Kconfig          |   4 ++
>>>  drivers/irqchip/Makefile         |   1 +
>>>  drivers/irqchip/irq-dumb-demux.c |  70 ++++++++++++++++++++
>>>  include/linux/irq.h              |  49 ++++++++++++++
>>>  include/linux/irqdomain.h        |   1 +
>>>  kernel/irq/Kconfig               |   5 ++
>>>  kernel/irq/Makefile              |   1 +
>>>  kernel/irq/chip.c                |  41 ++++++++++++
>>>  kernel/irq/dumb-demux-chip.c     | 140 +++++++++++++++++++++++++++++++++++++++
>>>  kernel/irq/handle.c              |  31 ++++++++-
>>>  kernel/irq/internals.h           |   3 +
>>>  11 files changed, 344 insertions(+), 2 deletions(-)
>>>  create mode 100644 drivers/irqchip/irq-dumb-demux.c
>>>  create mode 100644 kernel/irq/dumb-demux-chip.c

[..]

>>> +static void irq_dumb_demux_mask(struct irq_data *d)
>>> +{
>>> +	struct irq_chip_dumb_demux *demux = irq_data_get_irq_chip_data(d);
>>> +
>>> +	clear_bit(d->hwirq, &demux->unmasked);
>>> +
>>> +	if (!demux->unmasked)
>>> +		disable_irq_nosync(demux->src_irq);
>>> +}
>>> +
>>> +static void irq_dumb_demux_unmask(struct irq_data *d)
>>> +{
>>> +	struct irq_chip_dumb_demux *demux = irq_data_get_irq_chip_data(d);
>>> +	bool enable_src_irq = !demux->unmasked;
>>
>> Why this additional "bool" unlike the other function above?
> 
> Because set_bit will modify the unmasked status and we must check if it
> is equal to 0 (in other terms, all irqs are masked) before modifying it
> in order to know whether we should enable the src irq or not.

pfffff! ok, sorry for the noise then ;-)


>>> +
>>> +	set_bit(d->hwirq, &demux->unmasked);
>>> +
>>> +	if (enable_src_irq)
>>> +		enable_irq(demux->src_irq);
>>> +}
>>> +

[...]

Bye,
-- 
Nicolas Ferre
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