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

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Message-ID: <fd0257de-ce1a-40f3-a0b6-2f0c7dcee896@linux.intel.com>
Date: Sun, 1 Sep 2024 20:18:11 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: Thierry Reding <thierry.reding@...il.com>
Cc: baolu.lu@...ux.intel.com, 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 2024/8/28 23:27, Thierry Reding wrote:
> 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.

Yes, this is really what we want. I will update the patch series later.

Thanks,
baolu