| Message ID | 20250211-ep-msi-v15-2-bcacc1f2b1a9@nxp.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | PCI: EP: Add RC-to-EP doorbell with platform MSI controller | expand |
On Tue, 11 Feb 2025 19:21:55 +0000, Frank Li <Frank.Li@nxp.com> wrote: > > Add the flag IRQ_DOMAIN_FLAG_MSI_IMMUTABLE and the API function > irq_domain_is_msi_immutable() to check if the MSI controller retains an > immutable address/data pair during irq_set_affinity(). > > Ensure compatibility with MSI users like PCIe Endpoint Doorbell, which > require the address/data pair to remain unchanged after setup. Use this > function to verify if the MSI controller is immutable. Why is that a requirement? Why should a driver even care? M.
On Sat, Mar 01, 2025 at 11:10:35AM +0000, Marc Zyngier wrote: > On Tue, 11 Feb 2025 19:21:55 +0000, > Frank Li <Frank.Li@nxp.com> wrote: > > > > Add the flag IRQ_DOMAIN_FLAG_MSI_IMMUTABLE and the API function > > irq_domain_is_msi_immutable() to check if the MSI controller retains an > > immutable address/data pair during irq_set_affinity(). > > > > Ensure compatibility with MSI users like PCIe Endpoint Doorbell, which > > require the address/data pair to remain unchanged after setup. Use this > > function to verify if the MSI controller is immutable. > > Why is that a requirement? Why should a driver even care? At v9, there were detail discussion about this https://lore.kernel.org/all/87v7w0s9a8.ffs@tglx/ let me summary: Host driver workflow like: 1. read address/data from shared memory (PC bar<n>) 2. write data to address to trigger doorbell. 1 and 2 is not atomic. So EP side may call set_affinity function during 1 and 2, address/data may be changed in some MSI provider, so 2 write to previous address/data pair, which may not existed or map to other place and cause write to unexpected place. Frank > > M. > > -- > Without deviation from the norm, progress is not possible.
diff --git a/include/linux/irqdomain.h b/include/linux/irqdomain.h index e432b6a12a32f..3dbe05d8740e6 100644 --- a/include/linux/irqdomain.h +++ b/include/linux/irqdomain.h @@ -231,6 +231,9 @@ enum { /* Irq domain must destroy generic chips when removed */ IRQ_DOMAIN_FLAG_DESTROY_GC = (1 << 10), + /* Address and data pair is mutable when irq_set_affinity() */ + IRQ_DOMAIN_FLAG_MSI_IMMUTABLE = (1 << 11), + /* * Flags starting from IRQ_DOMAIN_FLAG_NONCORE are reserved * for implementation specific purposes and ignored by the @@ -692,6 +695,10 @@ static inline bool irq_domain_is_msi_device(struct irq_domain *domain) return domain->flags & IRQ_DOMAIN_FLAG_MSI_DEVICE; } +static inline bool irq_domain_is_msi_immutable(struct irq_domain *domain) +{ + return domain->flags & IRQ_DOMAIN_FLAG_MSI_IMMUTABLE; +} #else /* CONFIG_IRQ_DOMAIN_HIERARCHY */ static inline int irq_domain_alloc_irqs(struct irq_domain *domain, unsigned int nr_irqs, int node, void *arg)
Add the flag IRQ_DOMAIN_FLAG_MSI_IMMUTABLE and the API function irq_domain_is_msi_immutable() to check if the MSI controller retains an immutable address/data pair during irq_set_affinity(). Ensure compatibility with MSI users like PCIe Endpoint Doorbell, which require the address/data pair to remain unchanged after setup. Use this function to verify if the MSI controller is immutable. Signed-off-by: Frank Li <Frank.Li@nxp.com> --- change from v14 to v15 - none change from v13 to v14 - Roll back to v12 version because Marc Zyngier have concern about add DOMAIN_BUS_DEVICE_PCI_EP_MSI. https://lore.kernel.org/imx/861pxfq315.wl-maz@kernel.org/ Change from v11 to v12 - change to IRQ_DOMAIN_FLAG_MSI_IMMUTABLE to minimized the code change. --- include/linux/irqdomain.h | 7 +++++++ 1 file changed, 7 insertions(+)