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

[Lu Baolu]

Hi Leon,

On 2/8/21 4:21 PM, Leon Romanovsky wrote:
> On Wed, Feb 03, 2021 at 12:56:44PM -0800, Megha Dey wrote:
> > From: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> >
> > 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@xxxxxxxxxxxx>
> > Cc: Leon Romanovsky <leon@xxxxxxxxxx>
> > Cc: Kevin Tian <kevin.tian@xxxxxxxxx>
> > Suggested-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > Link: https://lore.kernel.org/linux-pci/87pn4nk7nn.fsf@xxxxxxxxxxxxxxxxxxxxxxx/
> > Link: https://lore.kernel.org/linux-pci/877dqrnzr3.fsf@xxxxxxxxxxxxxxxxxxxxxxx/
> > Link: https://lore.kernel.org/linux-pci/877dqqmc2h.fsf@xxxxxxxxxxxxxxxxxxxxxxx/
> > Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> > Signed-off-by: Megha Dey <megha.dey@xxxxxxxxx>
> > ---
> >   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?.

The added code is only called when DEVICE_MSI is configured.

> 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.

Yes. This looks better.

> Thanks

Best regards,
baolu