linux-kernel - Re: [PATCH 3/3] drm/tegra: Remove call to iommu_domain

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Message-ID: <qyvyd2ftebjlgmzyayfvxsqa64c4wgx7keix3a6eexdspbvawy@a5ffnm5h5tgp>
Date: Wed, 28 Aug 2024 17:27:24 +0200
From: Thierry Reding <thierry.reding@...il.com>
To: Lu Baolu <baolu.lu@...ux.intel.com>
Cc: Karol Herbst <kherbst@...hat.com>, Lyude Paul <lyude@...hat.com>, 
	Danilo Krummrich <dakr@...hat.com>, David Airlie <airlied@...il.com>, 
	Daniel Vetter <daniel@...ll.ch>, Jonathan Hunter <jonathanh@...dia.com>, 
	Sandy Huang <hjc@...k-chips.com>, Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
	Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, 
	Mikko Perttunen <mperttunen@...dia.com>, Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>, 
	Robin Murphy <robin.murphy@....com>, Jason Gunthorpe <jgg@...pe.ca>, 
	Kevin Tian <kevin.tian@...el.com>, dri-devel@...ts.freedesktop.org, nouveau@...ts.freedesktop.org, 
	linux-tegra@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	linux-rockchip@...ts.infradead.org, linux-media@...r.kernel.org, iommu@...ts.linux.dev, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] drm/tegra: Remove call to iommu_domain_alloc()

On Mon, Aug 12, 2024 at 03:10:34PM GMT, Lu Baolu wrote:
> Commit <17de3f5fdd35> ("iommu: Retire bus ops") removes iommu ops from
> the bus structure. The iommu subsystem no longer relies on bus for
> operations. So iommu_domain_alloc() interface is no longer relevant.
> 
> Normally, iommu_paging_domain_alloc() could be a replacement for
> iommu_domain_alloc() if the caller has the right device for IOMMU API
> use. Unfortunately, this is not the case for this driver.
> 
> Iterate the devices on the platform bus and find a suitable device
> whose device DMA is translated by an IOMMU. Then use this device to
> allocate an iommu domain. The iommu subsystem prevents domains
> allocated by one iommu driver from being attached to devices managed
> by any different iommu driver.
> 
> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
> Link: https://lore.kernel.org/r/20240610085555.88197-20-baolu.lu@linux.intel.com
> ---
>  drivers/gpu/drm/tegra/drm.c | 34 +++++++++++++++++++++++++---------
>  1 file changed, 25 insertions(+), 9 deletions(-)

Actually I think we can just do something like this:

--- >8 ---
diff --git a/drivers/gpu/drm/tegra/drm.c b/drivers/gpu/drm/tegra/drm.c
index d9f0728c3afd..d35e411d536b 100644
--- a/drivers/gpu/drm/tegra/drm.c
+++ b/drivers/gpu/drm/tegra/drm.c
@@ -1150,7 +1150,7 @@ static int host1x_drm_probe(struct host1x_device *dev)
 	}
 
 	if (host1x_drm_wants_iommu(dev) && iommu_present(&platform_bus_type)) {
-		tegra->domain = iommu_domain_alloc(&platform_bus_type);
+		tegra->domain = iommu_paging_domain_alloc(dev->dev.parent);
 		if (!tegra->domain) {
 			err = -ENOMEM;
 			goto free;
--- >8 ---

That refers to the physical device that the host1x_device virtual device
was instantiated from and is a common parent to all physical devices
that are part of the virtual device.

Thierry

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