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

[Neil Armstrong <neil.armstrong@linaro.org>]

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


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