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

[Neil Armstrong]

On 3/5/26 12:08, Krzysztof Kozlowski wrote:
> 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.


No it is not, canvas was used for a long time for the display and video processing side.

It's absolutely not like an IOMMU, the diagram is quite clear.

Neil

> Best regards,
> Krzysztof