linux-kernel - Re: [PATCH v6 2/7] iommu/riscv: Add RISC-V IOMMU platform device driver

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Date: Wed, 5 Jun 2024 12:41:53 -0700
From: Tomasz Jeznach <tjeznach@...osinc.com>
To: Andrew Jones <ajones@...tanamicro.com>
Cc: Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>, 
	Robin Murphy <robin.murphy@....com>, Paul Walmsley <paul.walmsley@...ive.com>, 
	Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>, 
	Anup Patel <apatel@...tanamicro.com>, Sunil V L <sunilvl@...tanamicro.com>, 
	Nick Kossifidis <mick@....forth.gr>, Sebastien Boeuf <seb@...osinc.com>, Rob Herring <robh+dt@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, devicetree@...r.kernel.org, 
	iommu@...ts.linux.dev, linux-riscv@...ts.infradead.org, 
	linux-kernel@...r.kernel.org, linux@...osinc.com, 
	Lu Baolu <baolu.lu@...ux.intel.com>
Subject: Re: [PATCH v6 2/7] iommu/riscv: Add RISC-V IOMMU platform device driver

On Mon, Jun 3, 2024 at 5:59 AM Andrew Jones <ajones@...tanamicro.com> wrote:
>
> On Fri, May 24, 2024 at 12:34:42PM GMT, Tomasz Jeznach wrote:
> ...
> > +static struct platform_driver riscv_iommu_platform_driver = {
> > +     .probe = riscv_iommu_platform_probe,
> > +     .remove_new = riscv_iommu_platform_remove,
>
> Hi Tomasz,
>
> I think we should also support .shutdown (just turn the IOMMU off?),
> otherwise the IOMMU driver reports EBUSY and fails to initialize when
> rebooting.
>
> Same comment for the PCI driver.
>

I've been testing patches with added shutdown handlers, also looking
at reboot notifier hooks. In both cases, devices actively running DMA
traffic at system shutdown (eg. storage) might be affected by
too-early IOMMU disable call. This topic was already brought up in the
discussion [1] about kexec reboot flow.

In this series I'd prefer to keep the IOMMU active during shutdown,
and prepare the RISC-V IOMMU shutdown sequence implementation as a
separate series, as it will involve more risc-v reboot rework to
guarantee ordering of the shutdown callbacks. In a normal reboot
cycle, firmware/hardware reset should bring IOMMU to known
out-of-reset state anyway.

[1] https://lore.kernel.org/linux-iommu/059ae516-aed4-4836-a2ca-aff150ff428d@arm.com/

Best,
- Tomasz

> Thanks,
> drew