Re: [PATCH v4 4/5] dma: swiotlb: Add an overridable architecture pool opt-out

[sashiko-bot@kernel.org]

> On x86, iommu=off historically prevented SWIOTLB initialization by not
> setting SWIOTLB_INIT_ADDRESSING_LIMIT. This overloads that flag: it
> controls both whether a pool is selected and where the pool is
> allocated. If another requirement, swiotlb=force selects a pool
> independently, omitting SWIOTLB_INIT_ADDRESSING_LIMIT may place it above
> the addressable range of devices which need bounce buffering.
> 
> Add SWIOTLB_INIT_FORCE_DISABLE to let an architecture opt out of normal
> pool initialization without discarding the pool placement constraints.
> 
> Unlike swiotlb_force_disable, which is set by swiotlb=noforce and
> unconditionally prevents pool initialization, the new flag is an
> architecture default. Explicit requirements such as memory encryption,
> architecture remapping, or swiotlb=force take precedence over it.
> 
> iommu=soft retains SWIOTLB_INIT_ADDRESSING_LIMIT because it requests
> software bounce buffering for devices whose DMA masks cannot address all
> system memory. Such devices must be able to reach the bounce pool.
> 
> Clear both flags for Xen because Xen explicitly requires a remapped
> SWIOTLB pool and may allocate it anywhere in directly mapped memory.
> 
> With no override, iommu=off disables both hardware IOMMU translation and
> SWIOTLB bouncing. Direct DMA remains available; mappings outside a
> device's addressable range fail instead of being bounced.
> 
> Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org>

Sashiko has reviewed this patch and found no issues. It looks great!

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Sashiko AI review · https://sashiko.dev/#/patchset/20260914070135.313337-1-aneesh.kumar@kernel.org?part=4