Using iommu-addresses beyond reserved-memory

Using iommu-addresses beyond reserved-memory

[Konrad Dybcio]

Hi,

We're exploring the use of iommu-addresses due to hw specifics where memory
regions for some devices must be mapped in a given range.

iommu-addresses currently allows us to achieve that, but it's incredibly janky..
To achieve what we need, one has to:

1. define a negative of the desired region (i.e. reserve all memory except where
we want the allocations to happen)
2. pass that to a dt (sub)node as a memory region
(3. pray that you reserved enough memory after the region and there's no board
    with a larger amount of RAM down the line)

Now, the obvious idea is to redefine this property to consume the **allowed**
ranges on ""normal"" devices' nodes (i.e. not under /reserved-memory) - would
that be an acceptable approach? We're totally open to suggestions

Konrad

Re: Using iommu-addresses beyond reserved-memory

[Vikash Garodia]

On 5/1/2025 2:05 AM, Konrad Dybcio wrote:
> Hi,
> 
> We're exploring the use of iommu-addresses due to hw specifics where memory
> regions for some devices must be mapped in a given range.
> 
> iommu-addresses currently allows us to achieve that, but it's incredibly janky..
> To achieve what we need, one has to:
> 
> 1. define a negative of the desired region (i.e. reserve all memory except where
> we want the allocations to happen)
> 2. pass that to a dt (sub)node as a memory region
> (3. pray that you reserved enough memory after the region and there's no board
>     with a larger amount of RAM down the line)
> 
> Now, the obvious idea is to redefine this property to consume the **allowed**
> ranges on ""normal"" devices' nodes (i.e. not under /reserved-memory) - would
> that be an acceptable approach? We're totally open to suggestions

Any suggestions ?

Regards,
Vikash