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 29-09-2026 01:44 pm, Stephan Gerhold wrote:
> On Mon, Sep 28, 2026 at 04:02:47PM +0530, Vishnu Santhosh wrote:
>> 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, the approach looks good to me. You received some comments from
> others and Sashiko already, so I will make a more thorough review from
> my side once you have addressed (or at least considered) them for v3.
>
> Thanks,
> Stephan

Thanks for confirming the approach. I will address the remaining comments
as well, so that you can proceed with thorough review.

Thanks,
Vishnu