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

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Message-ID: <CAK9=C2XKg5jBxBtrWMvQP--8Yb4ACFZFyX4wrtLy1efH7hO9ow@mail.gmail.com>
Date:   Thu, 15 Jun 2023 11:16:35 +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 10:20 PM Jason Gunthorpe <jgg@...pe.ca> 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@...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.
>
> 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