Re: [PATCH] iommu: Add RISC-V IOMMU driver

On Mon, Aug 17, 2026 at 09:18:23AM -0500, Anirudh Srinivasan wrote:
>
> Hi Tim,
>
> On Sun, Aug 16, 2026 at 7:20 AM Tim Ouyang <[email protected]> wrote:
> >
> > On Mon, Aug 03, 2026 at 03:06:12PM -0500, Anirudh Srinivasan wrote:
> > > Adds a basic driver for IOMMUs that conform to the RISC-V IOMMU
> > > specification. This driver sets up the IOMMU in bare mode so that
> > > peripherals requiring DMA in U-Boot can function.
> >
> > Would you consider adding support for SPL?
>
> I don't have an easy way to test this. This will have to be done later.

OK, let’s just move forward with the U-Boot proper part for now.

> > > +#define RISCV_IOMMU_DDTP_TIMEOUT          10000000
> >
> > Although the timeout aligns with Linux’s, it may still be too lengthy
> > for the bootloader stage.
>
> What value do you suggest? Seems like none of the other iommu drivers
> use timeouts, so I'm not sure what to pick.

I think a one-second timeout should be sufficient on real SoCs, while
three seconds should accommodate slower FPGA implementations.
--
Best regards,
Tim Ouyang