Re: [RFC PATCH] PCI: hv: Avoid the retarget interrupt hypercall in irq_unmask() on ARM64

[Boqun Feng]

On Wed, Feb 09, 2022 at 10:12:20AM -0600, Bjorn Helgaas wrote:
> On Wed, Feb 09, 2022 at 10:37:20AM +0800, Boqun Feng wrote:
> > On ARM64 Hyper-V guests, SPIs are used for the interrupts of virtual PCI
> > devices, and SPIs can be managed directly via GICD registers. Therefore
> > the retarget interrupt hypercall is not needed on ARM64.
> > 
> > The retarget interrupt hypercall related code is now put in a helper
> > function and only called on x86.
> > 
> > Signed-off-by: Boqun Feng <boqun.feng@xxxxxxxxx>
> > ---
> >  drivers/pci/controller/pci-hyperv.c | 11 +++++++++--
> >  1 file changed, 9 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c
> > index 20ea2ee330b8..80aa33ef5bf0 100644
> > --- a/drivers/pci/controller/pci-hyperv.c
> > +++ b/drivers/pci/controller/pci-hyperv.c
> > @@ -1457,7 +1457,7 @@ static void hv_irq_mask(struct irq_data *data)
> >  }
> >  
> >  /**
> > - * hv_irq_unmask() - "Unmask" the IRQ by setting its current
> > + * __hv_irq_unmask() - "Unmask" the IRQ by setting its current
> >   * affinity.
> >   * @data:	Describes the IRQ
> >   *
> > @@ -1466,7 +1466,7 @@ static void hv_irq_mask(struct irq_data *data)
> >   * is built out of this PCI bus's instance GUID and the function
> >   * number of the device.
> >   */
> > -static void hv_irq_unmask(struct irq_data *data)
> > +static void __hv_irq_unmask(struct irq_data *data)
> >  {
> >  	struct msi_desc *msi_desc = irq_data_get_msi_desc(data);
> >  	struct hv_retarget_device_interrupt *params;
> > @@ -1569,6 +1569,13 @@ static void hv_irq_unmask(struct irq_data *data)
> >  	if (!hv_result_success(res) && hbus->state != hv_pcibus_removing)
> >  		dev_err(&hbus->hdev->device,
> >  			"%s() failed: %#llx", __func__, res);
> > +}
> > +
> > +static void hv_irq_unmask(struct irq_data *data)
> > +{
> > +	/* Only use a hypercall on x86 */
> 
> This comment isn't useful because it only repeats what we can already
> see from the "IS_ENABLED(CONFIG_X86)" below and it doesn't say
> anything about *why*.
> 
> Didn't we just go though an exercise of adding interfaces for
> arch-specific things, i.e., 831c1ae725f7 ("PCI: hv: Make the code arch
> neutral by adding arch specific interfaces")?  Maybe this should be
> another such interface?
> 
> If you add Hyper-V support for a third arch, this #ifdef will likely
> be silently incorrect.  If you add an interface, there's at least a
> clue that this needs to be evaluated.
> 

You are right. I will make __hv_irq_unmask() as an arch-specific
interface in the next version (probably with a better name). Thank you!

Regards,
Boqun

> > +	if (IS_ENABLED(CONFIG_X86))
> > +		__hv_irq_unmask(data);
> >  
> >  	if (data->parent_data->chip->irq_unmask)
> >  		irq_chip_unmask_parent(data);
> > -- 
> > 2.35.1
> >