linux-kernel - Re: [PATCH 11/12] platform-msi: Add platform check for subdevice irq domain

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Date:   Mon, 8 Feb 2021 10:21:48 +0200
From:   Leon Romanovsky <leon@...nel.org>
To:     Megha Dey <megha.dey@...el.com>
Cc:     tglx@...utronix.de, linux-kernel@...r.kernel.org,
        dave.jiang@...el.com, ashok.raj@...el.com, kevin.tian@...el.com,
        dwmw@...zon.co.uk, x86@...nel.org, tony.luck@...el.com,
        dan.j.williams@...el.com, jgg@...lanox.com, kvm@...r.kernel.org,
        iommu@...ts.linux-foundation.org, alex.williamson@...hat.com,
        bhelgaas@...gle.com, maz@...nel.org, linux-pci@...r.kernel.org,
        baolu.lu@...ux.intel.com, ravi.v.shankar@...el.com
Subject: Re: [PATCH 11/12] platform-msi: Add platform check for subdevice irq
 domain

On Wed, Feb 03, 2021 at 12:56:44PM -0800, Megha Dey wrote:
> From: Lu Baolu <baolu.lu@...ux.intel.com>
>
> The pci_subdevice_msi_create_irq_domain() should fail if the underlying
> platform is not able to support IMS (Interrupt Message Storage). Otherwise,
> the isolation of interrupt is not guaranteed.
>
> For x86, IMS is only supported on bare metal for now. We could enable it
> in the virtualization environments in the future if interrupt HYPERCALL
> domain is supported or the hardware has the capability of interrupt
> isolation for subdevices.
>
> Cc: David Woodhouse <dwmw@...zon.co.uk>
> Cc: Leon Romanovsky <leon@...nel.org>
> Cc: Kevin Tian <kevin.tian@...el.com>
> Suggested-by: Thomas Gleixner <tglx@...utronix.de>
> Link: https://lore.kernel.org/linux-pci/87pn4nk7nn.fsf@nanos.tec.linutronix.de/
> Link: https://lore.kernel.org/linux-pci/877dqrnzr3.fsf@nanos.tec.linutronix.de/
> Link: https://lore.kernel.org/linux-pci/877dqqmc2h.fsf@nanos.tec.linutronix.de/
> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
> Signed-off-by: Megha Dey <megha.dey@...el.com>
> ---
>  arch/x86/pci/common.c       | 74 +++++++++++++++++++++++++++++++++++++++++++++
>  drivers/base/platform-msi.c |  8 +++++
>  include/linux/msi.h         |  1 +
>  3 files changed, 83 insertions(+)
>
> diff --git a/arch/x86/pci/common.c b/arch/x86/pci/common.c
> index 3507f45..263ccf6 100644
> --- a/arch/x86/pci/common.c
> +++ b/arch/x86/pci/common.c
> @@ -12,6 +12,8 @@
>  #include <linux/init.h>
>  #include <linux/dmi.h>
>  #include <linux/slab.h>
> +#include <linux/iommu.h>
> +#include <linux/msi.h>
>
>  #include <asm/acpi.h>
>  #include <asm/segment.h>
> @@ -724,3 +726,75 @@ struct pci_dev *pci_real_dma_dev(struct pci_dev *dev)
>  	return dev;
>  }
>  #endif
> +
> +#ifdef CONFIG_DEVICE_MSI

Sorry for my naive question, but I see it in all your patches in this series
and wonder why did you wrap everything with ifdefs?.

All *.c code is wrapped with those ifdefs, which is hard to navigate and
unlikely to give any code/size optimization benefit if kernel is compiled
without CONFIG_DEVICE_MSI. The more common approach is to put those
ifdef in the public header files and leave to the compiler to drop not
called functions.

Thanks