From: Jason Gunthorpe <jgg@nvidia.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Joao Martins <joao.m.martins@oracle.com>,
Arnd Bergmann <arnd@kernel.org>,
Kevin Tian <kevin.tian@intel.com>,
Yishai Hadas <yishaih@nvidia.com>,
Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>,
Alex Williamson <alex.williamson@redhat.com>,
Brett Creeley <brett.creeley@amd.com>,
oushixiong <oushixiong@kylinos.cn>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] vfio: mlx5, pds: add IOMMU_SUPPORT dependency
Date: Mon, 23 Oct 2023 11:19:55 -0300 [thread overview]
Message-ID: <20231023141955.GX3952@nvidia.com> (raw)
In-Reply-To: <5d7cb04d-9e79-43b9-9dd2-7d7803c93f4f@app.fastmail.com>
On Mon, Oct 23, 2023 at 04:02:11PM +0200, Arnd Bergmann wrote:
> On Mon, Oct 23, 2023, at 15:23, Jason Gunthorpe wrote:
> > On Mon, Oct 23, 2023 at 02:55:13PM +0200, Arnd Bergmann wrote:
> >> On Mon, Oct 23, 2023, at 14:37, Joao Martins wrote:
> >>
> >> Are there any useful configurations with IOMMU_API but
> >> not IOMMU_SUPPORT though? My first approach was actually
> >
> > IOMMU_SUPPORT is just the menu option in kconfig, it doesn't actually
> > do anything functional as far as I can tell
> >
> > But you can have IOMMU_API turned on without IOMMU_SUPPORT still on
> > power
> >
> > I think the right thing is to combine IOMMU_SUPPORT and IOMMU_API into
> > the same thing.
>
> I've had a closer look now and I think the way it is currently
> designed to be used makes some sense: IOMMU implementations almost
> universally depend on both a CPU architecture and CONFIG_IOMMU_SUPPORT,
> but select IOMMU_API. So if you enable IOMMU_SUPPORT on an
> architecture that has no IOMMU implementations, none of the drivers
> are visible and nothing happens. Similarly, almost all drivers
> using the IOMMU interface depend on IOMMU_API, so they can only
> be built if at least one IOMMU driver is configured.
Maybe, but I don't think we need such micro-optimization.
If someone selects 'enable IOMMU support' and doesn't turn on any
drivers then they should still get the core API. That is how a lot of
the kconfig stuff typically works in the kernel.
Similarly, if they don't select 'enable IOMMU support' then they
definitely shouldn't quitely get the core API turned on!
> diff --git a/drivers/gpu/drm/nouveau/Kconfig b/drivers/gpu/drm/nouveau/Kconfig
> index 4a79704b164f7..2902b89a48f17 100644
> --- a/drivers/gpu/drm/nouveau/Kconfig
> +++ b/drivers/gpu/drm/nouveau/Kconfig
> @@ -4,7 +4,7 @@ config DRM_NOUVEAU
> depends on DRM && PCI && MMU
> depends on (ACPI_VIDEO && ACPI_WMI && MXM_WMI) || !(ACPI && X86)
> depends on BACKLIGHT_CLASS_DEVICE
> - select IOMMU_API
> + depends on IOMMU_API
> select FW_LOADER
> select DRM_DISPLAY_DP_HELPER
> select DRM_DISPLAY_HDMI_HELPER
Like here, nouveau should still be compilable even if no iommu driver
was selected, and it should compile on arches without iommu drivers at
all.
Jason
next prev parent reply other threads:[~2023-10-23 14:20 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-23 11:55 [PATCH] vfio: mlx5, pds: add IOMMU_SUPPORT dependency Arnd Bergmann
2023-10-23 12:04 ` Jason Gunthorpe
2023-10-23 12:37 ` Joao Martins
2023-10-23 12:55 ` Arnd Bergmann
2023-10-23 13:23 ` Jason Gunthorpe
2023-10-23 14:02 ` Arnd Bergmann
2023-10-23 14:19 ` Jason Gunthorpe [this message]
2023-10-23 14:35 ` Arnd Bergmann
2023-10-23 14:43 ` Jason Gunthorpe
2023-10-23 14:52 ` Arnd Bergmann
2023-10-23 13:12 ` Jason Gunthorpe
2023-10-23 17:50 ` Joao Martins
2023-10-23 18:08 ` Jason Gunthorpe
2023-10-23 18:46 ` Arnd Bergmann
2023-10-23 20:23 ` Joao Martins
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