Re: [PATCH net-next v2 0/2] net: wwan: qcom_bam_dmux: Add restricted DMA pool support

[Vishnu Santhosh <vishnu.santhosh@oss.qualcomm.com>]

On 20-09-2026 08:32 am, Vishnu Santhosh wrote:
> Some Qualcomm SoCs, such as Shikra, run the modem in a separate security
> domain with restricted access to system memory. BAM-DMUX DMA mappings
> and BAM descriptor FIFOs must therefore be constrained to a designated
> memory region that can be shared with the modem. Accesses outside that
> region can trigger an XPU violation.
>
> Add memory-region and qcom,vmid properties to the BAM-DMUX binding.
> When qcom,vmid is present, the driver SCM-assigns the entire restricted
> DMA pool to the local and remote execution environments before requesting
> the DMA channels.
>
> The restricted pool then contains the BAM-DMUX mappings. When the BAM DMA
> controller references the same pool, its descriptor FIFOs are covered by
> the assignment as well.
>
> A related binding change allows the BAM DMA controller to use the same
> restricted pool for descriptor FIFO allocations:
>
> https://lore.kernel.org/all/20260920-qcom-bam-dma-vmid-ext-v2-1-4dbbff0e57c8@oss.qualcomm.com/
> ("dt-bindings: dma: qcom,bam-dma: Allow memory-region property")
>
> Signed-off-by: Vishnu Santhosh <vishnu.santhosh@oss.qualcomm.com>
> ---
> Changes in v2:
> - Replace the Shikra-specific compatible and coherent RX allocation with
>    memory-region and qcom,vmid properties.
> - Use a restricted DMA pool for BAM-DMUX mappings and BAM descriptor FIFOs.
> - SCM-assign the complete pool before requesting the DMA channels.
> - Validate the remote VMID and restricted DMA pool configuration.
> - Link to v1: https://lore.kernel.org/r/20260714-qcom-bam-dmux-vmid-ext-v1-0-3f29da7cca76@oss.qualcomm.com
>
> ---
> Vishnu Santhosh (2):
>        dt-bindings: net: qcom,bam-dmux: Add memory-region and qcom,vmid properties
>        net: wwan: qcom_bam_dmux: Assign restricted DMA pool to remote processor
>
>   .../devicetree/bindings/net/qcom,bam-dmux.yaml     | 38 +++++++++
>   drivers/net/wwan/Kconfig                           |  1 +
>   drivers/net/wwan/qcom_bam_dmux.c                   | 95 ++++++++++++++++++++++
>   3 files changed, 134 insertions(+)
> ---
> base-commit: 8830e65ed46de41f849eefb8ba227d4852c460f6
> change-id: 20260714-qcom-bam-dmux-vmid-ext-d9289db310c1
>
> Best regards,

Hi Stephan,

I followed your suggestion and updated v2 to use the restricted DMA pool.

Please let me know if this approach and the implementation look reasonable and
meets your expectations.

Thanks,
Vishnu