Re: [PATCH RFC v4 1/4] media: dt-bindings: Add Amlogic V4L2 video decoder

[Krzysztof Kozlowski <krzk@kernel.org>]

On 05/03/2026 12:01, Zhentao Guo wrote:
> 
>       2. Why canvas is needed?
> 
>  1. Since the ARM IOMMU HW is not integrated into the Amlogic SOCs,we
>     need canvas to prevent the DDR memory used by the decoder from being
>     rewrote by other hardware. Canvas provides the decoder with a
>     configurable DDR memory range, as well as hardware-based detection
>     and blocking for out-of-bounds access.
>   2. From the diagram above, we can see a lite CPU called AMRISC. AMRISC
>     is the controller of the decoder HW and the decoder driver needs to
>     access the decoder hardware through AMRISC. However, AMRISC is a
>     16-bit CPU and cannot directly handle 32-bit or 64-bit physical
>     addresses. Therefore, canvas is required to convert the addresses
>     into index to facilitate processing by the AMRISC core.

This suggests "Canvas" is IOMMU, thus use proper IOMMU abstractions and
you cannot have own phandle for it.

Best regards,
Krzysztof