Re: [RFC KERNEL PATCH v3 3/3] PCI/sysfs: Add gsi sysfs for pci_dev

["Roger Pau Monné" <roger.pau@citrix.com>]

On Tue, Dec 12, 2023 at 06:34:27AM +0000, Chen, Jiqian wrote:
> 
> On 2023/12/12 01:57, Roger Pau Monné wrote:
> > On Mon, Dec 11, 2023 at 12:15:19AM +0800, Jiqian Chen wrote:
> >> There is a need for some scenarios to use gsi sysfs.
> >> For example, when xen passthrough a device to dumU, it will
> >> use gsi to map pirq, but currently userspace can't get gsi
> >> number.
> >> So, add gsi sysfs for that and for other potential scenarios.
> >>
> >> Co-developed-by: Huang Rui <ray.huang@amd.com>
> >> Signed-off-by: Jiqian Chen <Jiqian.Chen@amd.com>
> >> ---
> >>  drivers/acpi/pci_irq.c  |  1 +
> >>  drivers/pci/pci-sysfs.c | 11 +++++++++++
> >>  include/linux/pci.h     |  2 ++
> >>  3 files changed, 14 insertions(+)
> >>
> >> diff --git a/drivers/acpi/pci_irq.c b/drivers/acpi/pci_irq.c
> >> index 630fe0a34bc6..739a58755df2 100644
> >> --- a/drivers/acpi/pci_irq.c
> >> +++ b/drivers/acpi/pci_irq.c
> >> @@ -449,6 +449,7 @@ int acpi_pci_irq_enable(struct pci_dev *dev)
> >>  		kfree(entry);
> >>  		return 0;
> >>  	}
> >> +	dev->gsi = gsi;
> > 
> > It would be better if the gsi if fetched without requiring calling
> > acpi_pci_irq_enable(), as the gsi doesn't require the interrupt to be
> > enabled.  The gsi is known at boot time and won't change for the
> > lifetime of the device.
> Do you have any suggest places to do this?

I'm not an expert on this, but drivers/pci/pci-sysfs.c would seem like
a better place, together with the rest of the resources.

Maybe my understanding is incorrect, but given the suggested placement
in acpi_pci_irq_enable() I think the device would need to bind the
interrupt in order for the gsi node to appear on sysfs?

Would the current approach work if the device is assigned to pciback
on the kernel command line, and thus never owned by any driver in
dom0?

> > 
> >>  
> >>  	rc = acpi_register_gsi(&dev->dev, gsi, triggering, polarity);
> >>  	if (rc < 0) {
> >> diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
> >> index 2321fdfefd7d..c51df88d079e 100644
> >> --- a/drivers/pci/pci-sysfs.c
> >> +++ b/drivers/pci/pci-sysfs.c
> >> @@ -71,6 +71,16 @@ static ssize_t irq_show(struct device *dev,
> >>  }
> >>  static DEVICE_ATTR_RO(irq);
> >>  
> >> +static ssize_t gsi_show(struct device *dev,
> >> +			struct device_attribute *attr,
> >> +			char *buf)
> >> +{
> >> +	struct pci_dev *pdev = to_pci_dev(dev);
> > 
> > const
> Do you mean "const struct pci_dev *pdev = to_pci_dev(dev);" ?

Yup.

Thanks, Roger.