Date:   Wed, 31 Oct 2018 15:38:48 +0000
From:   Phil Edworthy <phil.edworthy@...esas.com>
To:     Marc Zyngier <marc.zyngier@....com>
CC:     Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        "linux-renesas-soc@...r.kernel.org" 
        <linux-renesas-soc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v2 2/2] irqchip: Add support for Renesas RZ/N1 GPIO
 interrupt multiplexer

Hi Marc,

On 31 October 2018 15:31, Marc Zyngier wrote:
> On 31/10/18 15:09, Phil Edworthy wrote:
> > On 31 October 2018 08:02, Marc Zyngier wote:
> >> On Tue, 30 Oct 2018 10:44:38 +0000, Phil Edworthy wrote:
> >>>
> >>> On RZ/N1 devices, there are 3 Synopsys DesignWare GPIO blocks each
> >>> configured to have 32 interrupt outputs, so we have a total of 96
> >>> GPIO interrupts. All of these are passed to the GPIO IRQ Muxer,
> >>> which selects
> >>> 8 of the GPIO interrupts to pass onto the GIC. The interrupt signals
> >>> aren't latched, so there is nothing to do in this driver when an
> >>> interrupt is received, other than tell the corresponding GPIO block.
> >>>
> >>> Signed-off-by: Phil Edworthy <phil.edworthy@...esas.com>
> >>> ---
> >>> v2:
> >>>  - Use interrupt-map to allow the GPIO controller info to be specified
> >>>    as part of the irq.
> >>>  - Renamed struct and funcs from 'girq' to a more comprehenisble
> 'irqmux'.
> >>> ---
> >>>  drivers/irqchip/Kconfig        |  10 ++
> >>>  drivers/irqchip/Makefile       |   1 +
> >>>  drivers/irqchip/rzn1-irq-mux.c | 235
> >>> +++++++++++++++++++++++++++++++++
> >>>  3 files changed, 246 insertions(+)
> >>>  create mode 100644 drivers/irqchip/rzn1-irq-mux.c
> >>>
> >>> diff --git a/drivers/irqchip/Kconfig b/drivers/irqchip/Kconfig index
> >>> 96451b581452..3a60a8af60dd 100644
> >>> --- a/drivers/irqchip/Kconfig
> >>> +++ b/drivers/irqchip/Kconfig
> >>> @@ -204,6 +204,16 @@ config RENESAS_IRQC
> >>>  	select GENERIC_IRQ_CHIP
> >>>  	select IRQ_DOMAIN
> >>>
> >>> +config RENESAS_RZN1_IRQ_MUX
> >>> +	bool "Renesas RZ/N1 GPIO IRQ multiplexer support"
> >>> +	depends on ARCH_RZN1
> >>> +	select IRQ_DOMAIN
> >>> +	select IRQ_DOMAIN_HIERARCHY
> >>> +	help
> >>> +	  Say yes here to add support for the GPIO IRQ multiplexer
> >> embedded
> >>> +	  in Renesas RZ/N1 SoC devices. The GPIO IRQ Muxer selects which of
> >>> +	  the interrupts coming from the GPIO controllers are used.
> >>> +
> >>>  config ST_IRQCHIP
> >>>  	bool
> >>>  	select REGMAP
> >>> diff --git a/drivers/irqchip/Makefile b/drivers/irqchip/Makefile
> >>> index b822199445ff..b090f84dd42e 100644
> >>> --- a/drivers/irqchip/Makefile
> >>> +++ b/drivers/irqchip/Makefile
> >>> @@ -45,6 +45,7 @@ obj-$(CONFIG_SIRF_IRQ)			+=
> >> irq-sirfsoc.o
> >>>  obj-$(CONFIG_JCORE_AIC)			+= irq-jcore-aic.o
> >>>  obj-$(CONFIG_RENESAS_INTC_IRQPIN)	+= irq-renesas-intc-irqpin.o
> >>>  obj-$(CONFIG_RENESAS_IRQC)		+= irq-renesas-irqc.o
> >>> +obj-$(CONFIG_RENESAS_RZN1_IRQ_MUX)	+= rzn1-irq-mux.o
> >>>  obj-$(CONFIG_VERSATILE_FPGA_IRQ)	+= irq-versatile-fpga.o
> >>>  obj-$(CONFIG_ARCH_NSPIRE)		+= irq-zevio.o
> >>>  obj-$(CONFIG_ARCH_VT8500)		+= irq-vt8500.o
> >>> diff --git a/drivers/irqchip/rzn1-irq-mux.c
> >>> b/drivers/irqchip/rzn1-irq-mux.c new file mode 100644 index
> >>> 000000000000..767ce67e34d2
> >>> --- /dev/null
> >>> +++ b/drivers/irqchip/rzn1-irq-mux.c
> >>> @@ -0,0 +1,235 @@
> >>> +// SPDX-License-Identifier: GPL-2.0
> >>> +/*
> >>> + * RZ/N1 GPIO Interrupt Multiplexer
> >>> + *
> >>> + * Copyright (C) 2018 Renesas Electronics Europe Limited
> >>> + *
> >>> + * On RZ/N1 devices, there are 3 Synopsys DesignWare GPIO blocks
> >>> +each configured
> >>> + * to have 32 interrupt outputs, so we have a total of 96 GPIO
> interrupts.
> >>> + * All of these are passed to the GPIO IRQ Muxer, which selects 8
> >>> +of the GPIO
> >>> + * interrupts to pass onto the GIC.
> >>> + */
> >>> +
> >>> +#include <linux/bitops.h>
> >>> +#include <linux/interrupt.h>
> >>> +#include <linux/irq.h>
> >>> +#include <linux/irqchip/chained_irq.h> #include <linux/irqdomain.h>
> >>> +#include <linux/kernel.h> #include <linux/module.h> #include
> >>> +<linux/of_irq.h> #include <linux/of_platform.h>
> >>> +
> >>> +#define GPIO_IRQ_SPEC_SIZE	3
> >>> +#define MAX_NR_GPIO_CONTROLLERS	3
> >>> +#define MAX_NR_GPIO_IRQ		32
> >>> +#define MAX_NR_INPUT_IRQS	(MAX_NR_GPIO_CONTROLLERS *
> >> MAX_NR_GPIO_IRQ)
> >>> +#define MAX_NR_OUTPUT_IRQS	8
> >>> +
> >>> +struct irqmux_priv;
> >>> +struct irqmux_one {
> >>> +	unsigned int mapped_irq;
> >>> +	unsigned int input_irq_nr;
> >>> +	struct irqmux_priv *priv;
> >>> +};
> >>> +
> >>> +struct irqmux_priv {
> >>> +	struct device *dev;
> >>> +	struct irq_chip irq_chip;
> >>
> >> Do we really need this to be per-device? See below.
> > I thought we generally wanted everything to be per-device so that we
> > can cope when someone sticks two of these in a device. Am I wrong?
> 
> This only contains function pointers that are specific to a particular type of
> interrupt controller. Nothing in struct irq_chip is instance-specific.
Ah, I see!

<snip>
> >> OK, that's where I think we have a problem. Your irqchip structure
> >> seem to only be used to display a name?!?
> > Right, that wasn't the intention! So, how do I hook in my own
> > interrupt handler without calling irq_set_chip_and_handler()?
> > That's what led me to think I need an irq_chip instance.
> 
> That's the thing, you don't need it. each irq_chip is just a bunch of methods,
> and these methods apply to all the instances of the same controller.
> 
> >> To start with, that's not really the primary use for this object, and
> >> I'd like it to be a single static structure for the whole driver.
> >> Userspace doesn't need to know about the name, so please get rid of
> this.
> >>
> >> The real issue is that you build the whole thing as a chained
> >> interrupt controller, meaning that nothing controls the masking of
> >> the interrupt. If, as I understand it, this IP is an interrupt router
> >> that selects 8 out of 32 interrupts and passes them onto the GIC,
> >> then a noisy device can just take the whole CPU down by keeping the line
> asserted, and SW cannot mask it.
> > The interrupts into this mux come from GPIO blocks that do the
> > masking. The GPIO blocks in this case are standard Synopsys IP blocks.
> > There is nothing in the irq mux hardware that can mask them, or do
> > anything other than select which one to use, hence why this is a
> > chained interrupt controller. Should I be using something else in this case?
> 
> There are two cases:
> 1) there is 1:1 mapping between a used input and an output, leaving some
> input unused
> 2) there is an n:1 mapping between input and output, and all the input can be
> used at any given time
> 
> If what you have is (1), you need to implement an hierarchy.
> If what you have is (2), you need to implement a chained controller.
> 
> (1) requires you to revisit this driver, making it a lot more like ti's irq-crossbar
> (2) requires you to actually do some decoding in the chained handler
> 
> I believe you're in configuration (1). Am I right?
Right, it's a 1:1 mapping. The information about which input to be used needs
to be specified in dt.
I didn’t think I could implement a hierarchy that didn’t mask the interrupts, so I
need to go back over that and look again...

Many thanks!
Phil

> Thanks,
> 
> 	M.
> --
> Jazz is not dead. It just smells funny...

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