linux-kernel - Re: [PATCH v11 09/14] irqchip/riscv-imsic: Add support for PCI MSI irqdomain

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Message-ID: <87jzrbf5cw.fsf@all.your.base.are.belong.to.us>
Date:   Wed, 25 Oct 2023 10:55:59 +0200
From:   Björn Töpel <bjorn@...nel.org>
To:     Anup Patel <apatel@...tanamicro.com>
Cc:     Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Frank Rowand <frowand.list@...il.com>,
        Conor Dooley <conor+dt@...nel.org>,
        Marc Zyngier <maz@...nel.org>,
        Atish Patra <atishp@...shpatra.org>,
        Andrew Jones <ajones@...tanamicro.com>,
        Sunil V L <sunilvl@...tanamicro.com>,
        Saravana Kannan <saravanak@...gle.com>,
        Anup Patel <anup@...infault.org>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org
Subject: Re: [PATCH v11 09/14] irqchip/riscv-imsic: Add support for PCI MSI
 irqdomain

Anup Patel <apatel@...tanamicro.com> writes:

> On Tue, Oct 24, 2023 at 6:39 PM Björn Töpel <bjorn@...nel.org> wrote:
>>
>> Anup Patel <apatel@...tanamicro.com> writes:
>>
>> > The Linux PCI framework requires it's own dedicated MSI irqdomain so
>> > let us create PCI MSI irqdomain as child of the IMSIC base irqdomain.
>> >
>> > Signed-off-by: Anup Patel <apatel@...tanamicro.com>
>> > ---
>> >  drivers/irqchip/Kconfig                    |  7 +++
>> >  drivers/irqchip/irq-riscv-imsic-platform.c | 51 ++++++++++++++++++++++
>> >  drivers/irqchip/irq-riscv-imsic-state.h    |  1 +
>> >  3 files changed, 59 insertions(+)
>> >
>> > diff --git a/drivers/irqchip/Kconfig b/drivers/irqchip/Kconfig
>> > index bdd80716114d..c1d69b418dfb 100644
>> > --- a/drivers/irqchip/Kconfig
>> > +++ b/drivers/irqchip/Kconfig
>> > @@ -552,6 +552,13 @@ config RISCV_IMSIC
>> >       select IRQ_DOMAIN_HIERARCHY
>> >       select GENERIC_MSI_IRQ
>> >
>> > +config RISCV_IMSIC_PCI
>> > +     bool
>> > +     depends on RISCV_IMSIC
>> > +     depends on PCI
>> > +     depends on PCI_MSI
>> > +     default RISCV_IMSIC
>> > +
>> >  config EXYNOS_IRQ_COMBINER
>> >       bool "Samsung Exynos IRQ combiner support" if COMPILE_TEST
>> >       depends on (ARCH_EXYNOS && ARM) || COMPILE_TEST
>> > diff --git a/drivers/irqchip/irq-riscv-imsic-platform.c b/drivers/irqchip/irq-riscv-imsic-platform.c
>> > index 23d286cb017e..cdb659401199 100644
>> > --- a/drivers/irqchip/irq-riscv-imsic-platform.c
>> > +++ b/drivers/irqchip/irq-riscv-imsic-platform.c
>> > @@ -13,6 +13,7 @@
>> >  #include <linux/irqdomain.h>
>> >  #include <linux/module.h>
>> >  #include <linux/msi.h>
>> > +#include <linux/pci.h>
>> >  #include <linux/platform_device.h>
>> >  #include <linux/spinlock.h>
>> >  #include <linux/smp.h>
>> > @@ -215,6 +216,42 @@ static const struct irq_domain_ops imsic_base_domain_ops = {
>> >  #endif
>> >  };
>> >
>> > +#ifdef CONFIG_RISCV_IMSIC_PCI
>> > +
>> > +static void imsic_pci_mask_irq(struct irq_data *d)
>> > +{
>> > +     pci_msi_mask_irq(d);
>> > +     irq_chip_mask_parent(d);
>>
>> I've asked this before, but I still don't get why you need to propagate
>> to the parent? Why isn't masking on PCI enough?
>>
>
> We are using hierarchical IRQ domains where IMSIC-BASE is
> the root domain whereas IMSIC-PLAT domain (MSI irq domain
> for platform devices) and IMSIC-PCI domain (MSI irq domain
> for PCI devices). For hierarchical IRQ domains, if irq domain X
> does not implement irq_mask/unmask then the parent irq
> domain irq_mask/unmask is called with parent irq descriptor.
>
> Now for IMSIC-PCI domain, the PCI framework expects the
> pci_msi_mask/unmask_irq() functions to be called but if
> we directly point pci_msi_mask/unmask_irq() in the IMSIC-PCI
> irqchip then IMSIC-BASE (parent domain) irq_mask/umask
> won't be called hence the IRQ won't be masked/unmask.
> Due to this, we call both pci_msi_mask/unmask_irq() and
> irq_chip_mask/unmask_parent() for IMSIC-PCI domain.

Ok. I wont dig more into it for now! If the interrupt is disabled at
PCI, it seems a bit overkill to *also* mask it at the IMSIC level...


Björn