Re: [PATCH v3 07/11] irqchip/riscv-imsic: Improve IOMMU DMA support

[Anup Patel]

On Mon, May 15, 2023 at 6:23 PM Jason Gunthorpe <jgg@xxxxxxxxxx> wrote:
>
> On Mon, May 08, 2023 at 07:58:38PM +0530, Anup Patel wrote:
> > We have a separate RISC-V IMSIC MSI address for each CPU so changing
> > MSI (or IRQ) affinity results in re-programming of MSI address in
> > the PCIe (or platform) device.
> >
> > Currently, the iommu_dma_prepare_msi() is called only once at the
> > time of IRQ allocation so IOMMU DMA domain will only have mapping
> > for one MSI page. This means iommu_dma_compose_msi_msg() called
> > by imsic_irq_compose_msi_msg() will always use the same MSI page
> > irrespective to target CPU MSI address. In other words, changing
> > MSI (or IRQ) affinity for device using IOMMU DMA domain will not
> > work.
> >
> > To address above issue, we do the following:
> > 1) Map MSI pages for all CPUs in imsic_irq_domain_alloc()
> >    using iommu_dma_prepare_msi().
> > 2) Add a new iommu_dma_select_msi() API to select a specific
> >    MSI page from a set of already mapped MSI pages.
> > 3) Use iommu_dma_select_msi() to select a specific MSI page
> >    before calling iommu_dma_compose_msi_msg() in
> >    imsic_irq_compose_msi_msg().
>
> Is there an iommu driver somewhere in all this? I don't obviously see
> one?

Sorry for the delayed response.

The RISC-V IOMMU specification is frozen and will be ratified/released
anytime this month or next.
https://github.com/riscv-non-isa/riscv-iommu/releases/download/v1.0-rc6/riscv-iommu.pdf

The RISC-V IOMMU driver will be send-out on LKML pretty soon
https://github.com/tjeznach/linux/tree/tjeznach/riscv-iommu
which can be tested on QEMU
https://github.com/tjeznach/qemu/tree/tjeznach/riscv-iommu

>
> There should be no reason to use the dma-iommu.c stuff just to make
> interrupts work, that is only necessary if there is an iommu, and the
> platform architecture requires the iommu to have the MSI region
> programmed into IOPTEs.
>
> And I'd be much happier if we could clean this design up before risc-v
> starts using it too :\
>

Sure, I will send-out v4 in the next few days.

Regards,
Anup