Re: [PATCH v4 06/10] irqchip/riscv-imsic: Improve IOMMU DMA support

[Anup Patel]

On Wed, Jun 14, 2023 at 10:20 PM Jason Gunthorpe <jgg@xxxxxxxx> wrote:
>
> On Wed, Jun 14, 2023 at 09:47:53PM +0530, Anup Patel wrote:
> > On Wed, Jun 14, 2023 at 8:16 PM Jason Gunthorpe <jgg@xxxxxxxx> wrote:
> > >
> > > On Tue, Jun 13, 2023 at 09:04:11PM +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.
> > >
> > > You didn't answer my question from last time - there seems to be no
> > > iommu driver here so why are you messing with iommu_dma_prepare_msi()?
> > >
> > > This path is only for platforms that have IOMMU drivers that translate
> > > the MSI window. You should add this code to link the interrupt
> > > controller to the iommu driver when you introduce the iommu driver,
> > > not in this series?
> > >
> > > And, as I said before, I'd like to NOT see new users of
> > > iommu_dma_prepare_msi() since it is a very problematic API.
> > >
> > > This hacking of it here is not making it better :(
> >
> > I misunderstood your previous comments.
> >
> > We can certainly deal with this later when the IOMMU
> > driver is available for RISC-V. I will drop this patch in the
> > next revision.
>
> Not only just this patch but the calls to iommu_dma_prepare_msi() and
> related APIs in the prior patch too. Assume the MSI window is directly
> visible to DMA without translation.

Okay, I will remove iommu_dma_xyz() usage from IMSIC driver in the
next revision.

>
> When you come with an iommu driver we can discuss how best to proceed.

Yes, that's better.

Regards,
Anup