Re: [RFC PATCH 2/3] dma-buf: add a warn-only mode to DMABUF_DEBUG

[Jason Gunthorpe <jgg@nvidia.com>]

On Fri, Oct 09, 2026 at 03:21:47PM +0200, Christian König wrote:

> >> [ 1268.968710] CPU: 6 UID: 1000 PID: 29025 Comm: sway Not tainted 7.3-rc6+unreleased-arm64-cknow #1 PREEMPTLAZY  Debian 7.3~rc6-3
> >> [ 1268.968715] Hardware name: FriendlyElec NanoPC-T6 Plus (DT)
> >> [ 1268.968717] Call trace:
> >> [ 1268.968719]  show_stack+0x20/0x38 (C)
> >> [ 1268.968726]  dump_stack_lvl+0x60/0x80
> >> [ 1268.968730]  sg_dmabuf_cpu_access_warn.part.0+0x24/0x30
> >> [ 1268.968734]  sg_dmabuf_cpu_access_warn+0x34/0x38
> >> [ 1268.968739]  iommu_map_sg+0xc8/0x1e0
> >> [ 1268.968745]  rockchip_gem_iommu_map+0x8c/0x128 [rockchipdrm]
> >> [ 1268.968757]  rockchip_gem_prime_import_sg_table+0x58/0x160 [rockchipdrm]
> >> [ 1268.968761]  drm_gem_prime_import_dev+0xa8/0x1d0 [drm]
> >> [ 1268.968776]  drm_gem_prime_fd_to_handle+0x1a4/0x280 [drm]
> > 
> > So.. This is the exact same thing I need for iommufd.
> > 
> > rockchip is managing its own iommu domain and you cannot map to an
> > iommu domain without using a physical address.
> > 
> > Of course it is *completely* illegal to call iommu_map_sgtable() in the
> > importer side of a dmabuf.
> 
> Yeah we are deprecating this for the last ~5 years now. This bubbled
> up because I change to DMA-buf debug code to be enabled by default
> on DEBUG_KERNEL.
> 
> Rob is now working on a solution right now for MSM which should be
> used for rockchip as well.

So is Rob's plan is to remove the iommu_domains, somehow? Lately we've
been NAK'ing alot of the DT hacking that people have been doing in
other devices along those lines, so I wonder what that will look like.

It is probably easier to just fix things so the importer can get
things into an iommu_domain..

Jason