linux-kernel - Re: [PATCH] [EFI,PCI] Allow disabling PCI busmastering on bridges during boot

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Message-ID: <CACdnJuvTR2r_myJX2bQ8XTDw_HxM-EgqhVLaUJVCa+VQS+6Qrg@mail.gmail.com>
Date:   Wed, 4 Dec 2019 11:56:02 -0800
From:   Matthew Garrett <mjg59@...gle.com>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     linux-efi <linux-efi@...r.kernel.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        X86 ML <x86@...nel.org>, linux-pci <linux-pci@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] [EFI,PCI] Allow disabling PCI busmastering on bridges
 during boot

On Wed, Dec 4, 2019 at 11:50 AM Andy Lutomirski <luto@...capital.net> wrote:

> Wouldn't it also be applicable in the much simpler case where the
> firmware hands over control with no IOMMU configured but also with the
> busmastering bit cleared.  Does firmware do this?  Does the kernel
> currently configure the iOMMU before enabling busmastering?

We already handle this case - the kernel doesn't activate busmastering
until after it does IOMMU setup.