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

[Anup Patel <apatel@ventanamicro.com>]

On Tue, Oct 24, 2023 at 6:39 PM Björn Töpel <bjorn@kernel.org> wrote:
>
> Anup Patel <apatel@ventanamicro.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@ventanamicro.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.

The ARM GIC driver also uses hierarchical IRQ domains
even there same thing is done.
(Refer, first 30 lines of drivers/irqchip/irq-gic-v3-its-pci-msi.c)

Regards,
Anup