Re: [edk2-devel] [PATCH 1/1] EmbeddedPkg/NonCoherentIoMmuDxe: Make SetAttributes always succeed

["Ard Biesheuvel" <ardb@kernel.org>]

On Tue, 12 Mar 2024 at 17:38, Leif Lindholm <quic_llindhol@quicinc.com> wrote:
>
> On 2024-03-12 08:17, Ard Biesheuvel wrote:
> > From: Ard Biesheuvel <ardb@kernel.org>
> >
> > NonCoherentIoMmuSetAttribute() does nothing except return
> > EFI_UNSUPPORTED. This was fine when it was introduced, but now, the PCI
> > bus driver will fail a PCI I/O Map() operation if the SetAttributes
> > fails.
> >
> > So return EFI_SUCCESS instead.
>
> It's unclear to me why this change is safe (looking forward).
> Does NonCoherentIoMmuDxe also imply no IoMmu actually exists?
>

Basically. NonCoherentIoMmuDxe is just a vehicle to allow
NonCoherentDmaLib to be plugged into the PCI host bridge driver. It is
not intended to ever do anything more than that.


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