Re: [PATCH RFC 0/2] irqchip/ls-scfg-msi: add multi-MSI support

[Alexander Wilhelm]

On Thu, Aug 20, 2026 at 12:09:03PM -0400, Frank Li wrote:
> On Thu, Jul 16, 2026 at 12:14:59PM +0200, Alexander Wilhelm wrote:
> > This series enables multi-MSI (nr_irqs > 1) allocation on the Layerscape
> > SCFG MSI controller so PCI endpoints that request contiguous MSI vector
> > blocks (for example ath12k, which asks for 16 vectors: 3 MHI + 5 CE + 8 DP)
> > no longer fall back to single-MSI operation with all interrupts multiplexed
> > onto one CPU.
> >
> > The first patch is a preparation refactor: switch the hwirq bookkeeping
> > from find_first_zero_bit() / __set_bit() to bitmap_find_free_region() /
> > bitmap_release_region(), release the region on iommu_dma_prepare_msi()
> > error, and loop irq_domain_set_info() over nr_irqs. For the current
> > single-MSI case (order 0) this is functionally equivalent; the only
> > externally visible change is -ENOMEM instead of -ENOSPC on exhaustion.
> >
> > The second patch enables MSI_FLAG_MULTI_PCI_MSI on the parent domain, drops
> > the WARN_ON(nr_irqs != 1) guard, and statically pins each MSIR's chained
> > parent IRQ to its matching CPU in no-affinity mode. That pinning is
> > required because affinity mode only releases every (1 << ibs_shift)-th
> > hwirq and cannot satisfy aligned power-of-two allocations of size > 1;
> > users of multi-MSI must therefore boot with lsmsi=no-affinity.
> 
> what's happen if not set "lsmsi=no-affinity" at boot?

If "no-affinity" is not set, the system falls back to a single MSI vector as
before.


Best regards
Alexander Wilhelm