linux-kernel - Re: [PATCH] iommu: __iommu_attach_group: check for non-NULL blocking

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Message-ID: <58aabb55-0030-49df-81ed-d4a68174b57e@kernel.org>
Date: Mon, 29 Sep 2025 14:18:50 +0200
From: Hans Verkuil <hverkuil+cisco@...nel.org>
To: Jason Gunthorpe <jgg@...dia.com>
Cc: iommu@...ts.linux.dev, Linux Kernel <linux-kernel@...r.kernel.org>,
 Linux Media Mailing List <linux-media@...r.kernel.org>,
 Laurent Pinchart <laurent.pinchart@...asonboard.com>
Subject: Re: [PATCH] iommu: __iommu_attach_group: check for non-NULL
 blocking_domain

On 29/09/2025 14:07, Jason Gunthorpe wrote:
> On Mon, Sep 29, 2025 at 10:23:47AM +0200, Hans Verkuil wrote:
> 
>> Since I am unfamiliar with the iommu core code, I am uncertain whether I am
>> just papering over a bug elsewhere, or whether this is really the correct solution.
> 
> It is papering over something, group->domain is not supposed to be
> NULL at this point.. That probably means the iommu driver has not been

It's group->blocking_domain that's NULL, not group->domain.

Regards,

	Hans

> fully setup yet.
> 
> This is ARM32? It should have gone down this path:
> 
> static int iommu_get_default_domain_type(struct iommu_group *group,
> 					 int target_type)
> {
> 	if (IS_ENABLED(CONFIG_ARM_DMA_USE_IOMMU)) {
> 		static_assert(!(IS_ENABLED(CONFIG_ARM_DMA_USE_IOMMU) &&
> 				IS_ENABLED(CONFIG_IOMMU_DMA)));
> 		driver_type = IOMMU_DOMAIN_IDENTITY;
> 
> And I thought there shouldn't be a way to get here:
> 
>> drivers/media/platform/ti/omap3isp/isp.c, function isp_attach_iommu().
> 
> With a NULL group->domain?
> 
> Maybe it didn't call iommu_setup_default_domain() in the right
> sequence for some reason?
> 
> Can you inspect around this?
> 
> Jason