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

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Date:   Wed, 14 Jun 2023 21:47:53 +0530
From:   Anup Patel <apatel@...tanamicro.com>
To:     Jason Gunthorpe <jgg@...pe.ca>
Cc:     Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Marc Zyngier <maz@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Robin Murphy <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Atish Patra <atishp@...shpatra.org>,
        Andrew Jones <ajones@...tanamicro.com>,
        Conor Dooley <conor@...nel.org>,
        Saravana Kannan <saravanak@...gle.com>,
        Anup Patel <anup@...infault.org>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, iommu@...ts.linux.dev,
        Vincent Chen <vincent.chen@...ive.com>
Subject: Re: [PATCH v4 06/10] irqchip/riscv-imsic: Improve IOMMU DMA support

On Wed, Jun 14, 2023 at 8:16 PM Jason Gunthorpe <jgg@...pe.ca> 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.

Regards,
Anup