linux-kernel - Re: [PATCH] ARM: pxa: fix lubbock interrupts handling

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Date:	Fri, 28 Nov 2014 14:30:05 +0100
From:	Robert Jarzmik <robert.jarzmik@...e.fr>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Daniel Mack <daniel@...que.org>,
	Haojian Zhuang <haojian.zhuang@...il.com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ARM: pxa: fix lubbock interrupts handling

Thomas Gleixner <tglx@...utronix.de> writes:

> So what is the relationship between installing that chained handler
> and that gpio-pxa probe stuff?
The relation is in gpio-pxa probe, look at the extract of pxa_gpio_probe() :
pxa_gpio_probe()
		irq = gpio_to_irq(0);
		irq_set_chip_and_handler(irq, &pxa_muxed_gpio_chip,
					 handle_edge_irq);
		set_irq_flags(irq, IRQF_VALID | IRQF_PROBE);
		irq_set_chained_handler(IRQ_GPIO0, pxa_gpio_demux_handler);

Now look at the extract from the former lubbock_init_irq() :
lubbock_init_irq()
		irq = PXA_GPIO_TO_IRQ(0);
		irq_set_chained_handler(irq, lubbock_irq_handler);
		irq_set_irq_type(irq, IRQ_TYPE_EDGE_FALLING);

Given that gpio_to_irq(0) = PXA_GPIO_TO_IRQ(0), see how these 2 are fighting to
install the handler, and how the resulting installed handler depends on the
order of execution of pxa_gpio_to_irq() wrt lubbock_init_irq().

> And why is the GPIO0 interrupt handled from arch code rather than from
> a regular driver setup, which depends on the availablity of the GPIO
> driver?
Ah that's a good question. Maybe the answer is that there is no driver in this
case.
When I say "no driver", it's because this interrupt is a consequence of the
IO-Board (or motherboard) wiring topology.

I think I need to add a bit of context, so pardon my crude ascii-art style, and
see in the lubbock case, we have this wiring (list of IPs not exhaustive, and
gates to mask each XXX irq not added) :

IPs on Motherboard          Gates on motherboard                       SoC

+-------------+              +-------+
|  SMC Lan    | --lan irq--- | Latch | -
+-------------+              |       |  \                      +------PXA-----+
                             |       |   \                     |              |
+-------------+              |       |                         |+----------+  |
|   UDC Vbus  | --vbus irq-- | Latch | -- NOR gate -- GPIO0 -- ||GPIO block|  |
+-------------+              |       |                line     |+----------+  |
                             |       |   /                     |              |
+-------------+              |       |  /                      +--------------+
|   SA1111    | --sa11x irq--| Latch | -
+-------------+              +-------+

The "gates on motherboard" is what lubbock.c is describing, ie. the
interconnection on the motherboard. I don't see the device/driver model fitting
to describe these gates, do you ?

Cheers.

-- 
Robert
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