Re: [PATCH 3/3] drm/msm: detach the ARM DMA mapping before attaching our own domain

On Thu, Jul 30, 2026 at 03:42:58PM +0200, Konrad Dybcio wrote:
> On 7/30/26 3:29 PM, Dmitry Baryshkov wrote:
> > On ARM32 with CONFIG_ARM_DMA_USE_IOMMU, arch_setup_dma_ops() creates a
> > dma_iommu_mapping for every IOMMU-backed device and attaches its domain
> > to the device's IOMMU group. That domain is neither the group's default
> > nor its blocking domain, so when msm_iommu_new() later attaches the
> > domain the driver manages itself, __iommu_attach_group() refuses it:
> 
> [...]
> 
> > +#if defined(CONFIG_ARM_DMA_USE_IOMMU)
> > +#include <asm/dma-iommu.h>
> > +#else
> > +#define arm_iommu_detach_device(...)	({ })
> > +#define arm_iommu_release_mapping(...)	({ })
> > +#define to_dma_iommu_mapping(dev)	NULL
> > +#endif
> 
> I see this is prior art, but should we support this config being off?

Yes. For example, on arm64.

-- 
With best wishes
Dmitry