RE: [PATCH v2 6/6] drivers/pci/hyperv/arm64: vPCI MSI IRQ domain from DT

[Michael Kelley <mhklinux@outlook.com>]

From: Roman Kisel <romank@linux.microsoft.com> Sent: Tuesday, May 14, 2024 3:44 PM
> 
> The hyperv-pci driver uses ACPI for MSI IRQ domain configuration
> on arm64 thereby it won't be able to do that in the VTL mode where
> only DeviceTree can be used.

That sentence seems a bit weird.  How about:

   The hyperv-pci driver uses ACPI for MSI IRQ domain configuration on arm64.
   It won't be able to do that in the VTL mode where only DeviceTree can be used.

> 
> Update the hyperv-pci driver to discover interrupt configuration
> via DeviceTree.

"discover interrupt configuration"?   I think that's a cut-and-paste error
from the previous patch.

> 
> Signed-off-by: Roman Kisel <romank@linux.microsoft.com>
> ---
>  drivers/pci/controller/pci-hyperv.c | 13 ++++++++++---
>  include/linux/acpi.h                |  9 +++++++++
>  2 files changed, 19 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c
> index 1eaffff40b8d..ccc2b54206f4 100644
> --- a/drivers/pci/controller/pci-hyperv.c
> +++ b/drivers/pci/controller/pci-hyperv.c
> @@ -906,9 +906,16 @@ static int hv_pci_irqchip_init(void)
>  	 * way to ensure that all the corresponding devices are also gone and
>  	 * no interrupts will be generated.
>  	 */
> -	hv_msi_gic_irq_domain = acpi_irq_create_hierarchy(0, HV_PCI_MSI_SPI_NR,
> -							  fn, &hv_pci_domain_ops,
> -							  chip_data);
> +	if (acpi_disabled)
> +		hv_msi_gic_irq_domain = irq_domain_create_hierarchy(
> +			irq_find_matching_fwnode(fn, DOMAIN_BUS_ANY),
> +			0, HV_PCI_MSI_SPI_NR,
> +			fn, &hv_pci_domain_ops,
> +			chip_data);

Does the above really work?  It seems doubtful to me that irq_find_matching_fwnode()
always finds the parent domain that you want.  But I don't have a deep understanding
of how this works or is supposed to work, so I don't know for sure.

If the above *does* actually work for all cases, then should it also work for the ACPI
case?  Then you could avoid the messiness when acpi_irq_create_hierarchy() doesn't
exist.

> +	else
> +		hv_msi_gic_irq_domain = acpi_irq_create_hierarchy(0, HV_PCI_MSI_SPI_NR,
> +			fn, &hv_pci_domain_ops,
> +			chip_data);
> 
>  	if (!hv_msi_gic_irq_domain) {
>  		pr_err("Failed to create Hyper-V arm64 vPCI MSI IRQ domain\n");

I'm wondering if these are the only changes needed to make vPCI work on
arm64 with DeviceTree.  The DMA coherence issue I mentioned in the previous patch
definitely affects vPCI devices, so it needs to be fully understood and verified to work
correctly.

> diff --git a/include/linux/acpi.h b/include/linux/acpi.h
> index b7165e52b3c6..498cbb2c40a1 100644
> --- a/include/linux/acpi.h
> +++ b/include/linux/acpi.h
> @@ -1077,6 +1077,15 @@ static inline bool acpi_sleep_state_supported(u8 sleep_state)
>  	return false;
>  }
> 
> +static inline struct irq_domain *acpi_irq_create_hierarchy(unsigned int flags,
> +					     unsigned int size,
> +					     struct fwnode_handle *fwnode,
> +					     const struct irq_domain_ops *ops,
> +					     void *host_data)
> +{
> +	return NULL;
> +}
> +
>  #endif	/* !CONFIG_ACPI */
> 
>  extern void arch_post_acpi_subsys_init(void);
> --
> 2.45.0
> 


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