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Date:   Sat, 25 Sep 2021 10:31:19 +0100
Message-ID: <87a6k1atnc.wl-maz@kernel.org>
From:   Marc Zyngier <maz@kernel.org>
To:     "Lad, Prabhakar" <prabhakar.csengg@gmail.com>
Cc:     Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Geert Uytterhoeven <geert+renesas@glider.be>,
        Rob Herring <robh+dt@kernel.org>,
        Linus Walleij <linus.walleij@linaro.org>,
        Magnus Damm <magnus.damm@gmail.com>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>,
        Linux-Renesas <linux-renesas-soc@vger.kernel.org>,
        Biju Das <biju.das.jz@bp.renesas.com>
Subject: Re: [RFC PATCH v2 2/4] irqchip: Add RZ/G2L IA55 Interrupt Controller driver
In-Reply-To: <CA+V-a8vQ5J-Y4PdL5ZrEqbM-ohS1RRZvD8=7JL6GJCkg7ZOJwQ@mail.gmail.com>
References: <20210921193028.13099-1-prabhakar.mahadev-lad.rj@bp.renesas.com>
        <20210921193028.13099-3-prabhakar.mahadev-lad.rj@bp.renesas.com>
        <87v92pu7ad.wl-maz@kernel.org>
        <CA+V-a8vQ5J-Y4PdL5ZrEqbM-ohS1RRZvD8=7JL6GJCkg7ZOJwQ@mail.gmail.com>
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On Fri, 24 Sep 2021 23:27:21 +0100,
"Lad, Prabhakar" <prabhakar.csengg@gmail.com> wrote:
> 
> Hi Marc,
> 
> Thank you for the review.
> 
> On Fri, Sep 24, 2021 at 8:01 PM Marc Zyngier <maz@kernel.org> wrote:
> >
> > On Tue, 21 Sep 2021 20:30:26 +0100,
> > Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com> wrote:
> > >
> > > Add a driver for the Renesas RZ/G2L Interrupt Controller.
> > >
> > > This supports external pins being used as interrupts. It supports
> > > one line for NMI, 8 external pins and 32 GPIO pins (out of 123)
> > > to be used as IRQ lines.
> > >
> > > Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
> > > ---
> > >  drivers/irqchip/Kconfig             |   9 +
> > >  drivers/irqchip/Makefile            |   1 +
> > >  drivers/irqchip/irq-renesas-rzg2l.c | 393 ++++++++++++++++++++++++++++
> > >  drivers/soc/renesas/Kconfig         |   1 +
> > >  4 files changed, 404 insertions(+)
> > >  create mode 100644 drivers/irqchip/irq-renesas-rzg2l.c
> > >
> > > diff --git a/drivers/irqchip/Kconfig b/drivers/irqchip/Kconfig
> > > index 4d5924e9f766..b61dceac8628 100644
> > > --- a/drivers/irqchip/Kconfig
> > > +++ b/drivers/irqchip/Kconfig
> > > @@ -236,6 +236,15 @@ config RENESAS_RZA1_IRQC
> > >         Enable support for the Renesas RZ/A1 Interrupt Controller, to use up
> > >         to 8 external interrupts with configurable sense select.
> > >
> > > +config RENESAS_RZG2L_IRQC
> > > +     bool "Renesas RZ/G2L IRQC support" if COMPILE_TEST
> > > +     select GENERIC_IRQ_CHIP
> > > +     select IRQ_DOMAIN
> > > +     select IRQ_DOMAIN_HIERARCHY
> > > +     help
> > > +       Enable support for the Renesas RZ/G2L Interrupt Controller for external
> > > +       devices.
> > > +
> > >  config SL28CPLD_INTC
> > >       bool "Kontron sl28cpld IRQ controller"
> > >       depends on MFD_SL28CPLD=y || COMPILE_TEST
> > > diff --git a/drivers/irqchip/Makefile b/drivers/irqchip/Makefile
> > > index f88cbf36a9d2..8017786fbdac 100644
> > > --- a/drivers/irqchip/Makefile
> > > +++ b/drivers/irqchip/Makefile
> > > @@ -51,6 +51,7 @@ obj-$(CONFIG_RDA_INTC)                      += irq-rda-intc.o
> > >  obj-$(CONFIG_RENESAS_INTC_IRQPIN)    += irq-renesas-intc-irqpin.o
> > >  obj-$(CONFIG_RENESAS_IRQC)           += irq-renesas-irqc.o
> > >  obj-$(CONFIG_RENESAS_RZA1_IRQC)              += irq-renesas-rza1.o
> > > +obj-$(CONFIG_RENESAS_RZG2L_IRQC)     += irq-renesas-rzg2l.o
> > >  obj-$(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/irq-renesas-rzg2l.c b/drivers/irqchip/irq-renesas-rzg2l.c
> > > new file mode 100644
> > > index 000000000000..8057fdf6781b
> > > --- /dev/null
> > > +++ b/drivers/irqchip/irq-renesas-rzg2l.c
> > > @@ -0,0 +1,393 @@
> > > +// SPDX-License-Identifier: GPL-2.0
> > > +/*
> > > + * Renesas RZ/G2L IRQC Driver
> > > + *
> > > + * Copyright (C) 2021 Renesas Electronics Corporation.
> > > + */
> > > +
> > > +#include <linux/err.h>
> > > +#include <linux/init.h>
> > > +#include <linux/interrupt.h>
> > > +#include <linux/io.h>
> > > +#include <linux/irq.h>
> > > +#include <linux/irqchip/chained_irq.h>
> > > +#include <linux/irqdesc.h>
> > > +#include <linux/irqdomain.h>
> > > +#include <linux/module.h>
> > > +#include <linux/of_irq.h>
> > > +#include <linux/platform_device.h>
> > > +#include <linux/pm_runtime.h>
> > > +
> > > +#define IRQC_IRQ_START                       1
> > > +#define IRQC_IRQ_COUNT                       8
> > > +#define IRQC_TINT_START                      9
> > > +#define IRQC_TINT_COUNT                      32
> > > +#define IRQC_NUM_IRQ                 41
> > > +
> > > +#define ISCR                         0x10
> > > +#define IITSR                                0x14
> > > +#define TSCR                         0x20
> > > +#define TITSR0                               0x24
> > > +#define TITSR1                               0x28
> > > +#define TITSR0_MAX_INT                       16
> > > +#define TITSEL_WIDTH                 0x2
> > > +#define TSSR(n)                              (0x30 + ((n) * 4))
> > > +#define TIEN                         BIT(7)
> > > +#define TSSEL_SHIFT(n)                       (8 * (n))
> > > +#define TSSEL_MASK                   GENMASK(7, 0)
> > > +#define IRQ_MASK                     0x3
> > > +
> > > +#define TSSR_OFFSET(n)                       ((n) % 4)
> > > +#define TSSR_INDEX(n)                        ((n) / 4)
> > > +
> > > +#define TITSR_TITSEL_EDGE_RISING     0
> > > +#define TITSR_TITSEL_EDGE_FALLING    1
> > > +#define TITSR_TITSEL_LEVEL_HIGH              2
> > > +#define TITSR_TITSEL_LEVEL_LOW               3
> > > +
> > > +struct rzg2l_irqc_priv {
> > > +     void __iomem *base;
> > > +     struct device *dev;
> > > +     struct irq_chip chip;
> > > +     struct irq_domain *irq_domain;
> > > +     struct resource *irq[IRQC_NUM_IRQ];
> > > +     struct mutex irqc_mutex;
> > > +     struct mutex tint_mutex; /* Mutex to protect tint_slot bitmap */
> > > +     DECLARE_BITMAP(tint_slot, IRQC_TINT_COUNT);
> > > +};
> > > +
> > > +struct rzg2l_irqc_chip_data {
> > > +     struct rzg2l_irqc_priv *priv;
> > > +     int tint;
> > > +     int hwirq;
> > > +};
> > > +
> > > +static int rzg2l_tint_set_edge(struct rzg2l_irqc_priv *priv,
> > > +                            unsigned int hwirq, unsigned int type)
> > > +{
> > > +     u32 port = hwirq - IRQC_TINT_START;
> > > +     u8 sense;
> > > +     u32 reg;
> > > +
> > > +     switch (type & IRQ_TYPE_SENSE_MASK) {
> > > +     case IRQ_TYPE_EDGE_RISING:
> > > +             sense = TITSR_TITSEL_EDGE_RISING;
> > > +             break;
> > > +
> > > +     case IRQ_TYPE_EDGE_FALLING:
> > > +             sense = TITSR_TITSEL_EDGE_FALLING;
> > > +             break;
> > > +
> > > +     case IRQ_TYPE_LEVEL_HIGH:
> > > +             sense = TITSR_TITSEL_LEVEL_HIGH;
> > > +             break;
> > > +
> > > +     case IRQ_TYPE_LEVEL_LOW:
> > > +             sense = TITSR_TITSEL_LEVEL_LOW;
> > > +             break;
> > > +
> > > +     default:
> > > +             return -EINVAL;
> > > +     }
> > > +
> > > +     mutex_lock(&priv->irqc_mutex);
> >
> > Have you tested this code with lockdep? This cannot possibly work,
> > since all the irqchip callbacks are running under a per-irq raw
> > spinlock.
> >
> Yes I have tested with a GPIO pin being set as an interrupt.

[...]

You seem to have missed the key element above. *lockdep* is the
crucial part (and more specifically CONFIG_PROVE_LOCKING). My bet is
that you will get a huge splat telling you that your locking is bogus.

> > > +static void rzg2l_irqc_irq_enable(struct irq_data *d)
> > > +{
> > > +     struct rzg2l_irqc_chip_data *chip_data = d->chip_data;
> > > +     struct rzg2l_irqc_priv *priv = chip_data->priv;
> > > +
> > > +     if (chip_data->tint != -EINVAL) {
> > > +             u32 offset = chip_data->hwirq - IRQC_TINT_START;
> > > +             u32 tssr_offset = TSSR_OFFSET(offset);
> > > +             u8 tssr_index = TSSR_INDEX(offset);
> > > +             u32 reg;
> > > +
> > > +             irq_set_chained_handler_and_data(priv->irq[chip_data->hwirq]->start,
> > > +                                              rzg2l_irqc_tint_irq_handler,
> > > +                                              chip_data);
> > > +
> > > +             mutex_lock(&priv->irqc_mutex);
> > > +             reg = readl_relaxed(priv->base + TSSR(tssr_index));
> > > +             reg |= (TIEN | chip_data->tint) << TSSEL_SHIFT(tssr_offset);
> > > +             writel_relaxed(reg, priv->base + TSSR(tssr_index));
> > > +             mutex_unlock(&priv->irqc_mutex);
> > > +     }
> > > +}
> >
> > These two function make little sense. Why isn't the chained handler
> > wired once and for all?
> >
> you mean to move this during alloc callback? chained handler is
> registered only when an GPIO line is requested as interrupt as a
> result I am wiring only upon requests.

Why? Wiring a chained handler can be done as soon as the output
interrupt is known (which is probe time). There is no need to do that
on demand. However, this is the wrong model anyway, see below.

> 
> > > +
> > > +static int rzg2l_irqc_set_type(struct irq_data *d, unsigned int type)
> > > +{
> > > +     struct rzg2l_irqc_chip_data *chip_data = d->chip_data;
> > > +     struct rzg2l_irqc_priv *priv = chip_data->priv;
> > > +
> > > +     if (chip_data->tint != EINVAL)
> > > +             return rzg2l_tint_set_edge(priv, chip_data->hwirq, type);
> >
> > Inline this function here. There is no point in having this helper on
> > its own with a single call site.
> >
> Ok, I will make this inline.
> 
> > > +
> > > +     return -EINVAL;
> > > +}
> > > +
> > > +static int rzg2l_irqc_domain_alloc(struct irq_domain *domain, unsigned int virq,
> > > +                                unsigned int nr_irqs, void *arg)
> > > +{
> > > +     struct rzg2l_irqc_priv *priv = domain->host_data;
> > > +     struct rzg2l_irqc_chip_data *chip_data = NULL;
> > > +     struct irq_fwspec parent_fwspec;
> > > +     struct irq_fwspec *fwspec = arg;
> > > +     int tint = -EINVAL;
> > > +     irq_hw_number_t hwirq;
> > > +     int irq = -EINVAL;
> > > +     unsigned int type;
> > > +     int ret;
> > > +
> > > +     chip_data = kzalloc(sizeof(*chip_data), GFP_KERNEL);
> > > +     if (!chip_data)
> > > +             return -ENOMEM;
> >
> > Why do you need to allocate per interrupt chip-specific data?
> >
> To ack and trigger the virq in the domain. Let me know if there is a
> much better way of doing this.

This makes zero sense. The data structure associated with the irq_desc
should already give you everything you need.

And what is this 'virq'? If you are talking about the hwirq of the
triggering interrupt, you totally have the wrong end of the stick. A
chained interrupt controller shouldn't need to know that.

It really looks like you are abusing a chained interrupt controller,
while this really should be a hierarchical controller which maps a set
of input pins to a set of output pins, as you never seem to map
multiple inputs to a single output.

A hierarchical interrupt controller would give you the correct context
by construction, without having to add any extra data structure.

> 
> > > +
> > > +     ret = irq_domain_translate_twocell(domain, arg, &hwirq, &type);
> > > +     if (ret)
> > > +             return ret;
> > > +
> > > +     /*
> > > +      * When alloc has landed from pinctrl driver:
> > > +      * fwspec->param_count = 3
> > > +      * fwspec->param[0] = tint
> > > +      * fwspec->param[1] = type
> > > +      * fwspec->param[2] = 1
> > > +      */
> > > +     if (fwspec->param_count == 3 && fwspec->param[2]) {
> > > +             mutex_lock(&priv->tint_mutex);
> > > +             irq = bitmap_find_free_region(priv->tint_slot, IRQC_TINT_COUNT, get_order(1));
> >
> > I think you can replace this get_order() with the result.
> >
> > > +             if (irq < 0) {
> > > +                     mutex_unlock(&priv->tint_mutex);
> > > +                     return -ENOSPC;
> > > +             }
> > > +             mutex_unlock(&priv->tint_mutex);
> > > +             tint = hwirq;
> > > +             hwirq = irq + IRQC_TINT_START;
> > > +     }
> > > +
> > > +     chip_data->priv = priv;
> > > +     chip_data->tint = tint;
> > > +     chip_data->hwirq = hwirq;
> >
> > Really?
> Could you please elaborate here.
> 
> As per the current implementation here
> pinctrl->irqc->GIC
> The SoC supports 123 GPIO pins out of which a max of 32 can be
> configured as an interrupt line into the irqc.
> 
> keyboard {
>     compatible = "gpio-keys";
>     status = "okay";
> 
>    key-3 {
>        gpios = <&pinctrl RZG2L_GPIO(9, 0) GPIO_ACTIVE_HIGH>;
>        linux,code = <KEY_3>;
>        label = "SW3";
>         wakeup-source;
>     };
> };
> For example with the above the pinctrl driver passes interrupt number
> to be programmed into irqc corresponding to RZG2L_GPIO(9, 0),  type
> and third parameter tint indicating this is coming from pinctrl (as
> irqc supports gpio/irq/nmi). When this lands in the irqc domain with
> the above we find the first available slot from 32 interrupts and
> hwirq is set to  irq + IRQC_TINT_START if its first slot it would be
> 0+9.

Which proves my point. This isn't a chained interrupt controller *at
all*. this is just a mapper between 8 (out of 32) inputs to 8 outputs.

> 
> >
> > > +     ret = irq_domain_set_hwirq_and_chip(domain, virq, hwirq, &priv->chip, chip_data);
> > > +     if (ret)
> > > +             goto release_bitmap;
> > > +
> > > +     /* parent is GIC */
> > > +     parent_fwspec.fwnode = domain->parent->fwnode;
> > > +     parent_fwspec.param_count = 3;
> > > +     parent_fwspec.param[0] = 0; /* SPI */
> > > +     parent_fwspec.param[1] = priv->irq[hwirq]->start;
> > > +     parent_fwspec.param[2] = IRQ_TYPE_LEVEL_HIGH;
> > > +     ret = irq_domain_alloc_irqs_parent(domain, virq, nr_irqs, &parent_fwspec);
> This is the bit which is I am unclear about as I am requesting a
> chained handler I believe this should be done automatically and is not
> required. Is my understanding correct here?

Because you are mixing chained and hierarchical models. I even missed
the use of irq_domain_alloc_irqs_parent here, as the whole logic is
completely messed up.

	M.

-- 
Without deviation from the norm, progress is not possible.