[PATCH v7 0/3] misc: fastrpc: fix ADSP duplicate session creation

[Vinayak Katoch]

For ADSP, only a limited number of FastRPC context banks (CBs) are
available. Each CB supports a single session, which means only a few
processes can run on ADSP simultaneously. If all sessions are consumed
by fastrpc daemons, no session remains available when a user application
starts, causing the application to fail.

To work around this, some DT set:
  qcom,nsessions = <5>;
which duplicated sessions inline during context bank initialisation.
Upstream feedback indicated that this policy does not belong in DT and
should be handled at the driver level instead.

This series iterates over CB child nodes directly and synchronously,
replacing of_platform_populate() and of_platform_depopulate(), and
configures DMA/IOMMU for each CB itself since no driver binds to them
any more. It also moves the ADSP session duplication to the driver.
The qcom,nsessions binding is deprecated in the same series.

Signed-off-by: Vinayak Katoch <vinayak.katoch@xxxxxxxxxxxxxxxx>
---
Changes in v7:
- Call of_dma_configure() for each CB device, as no driver binds to
  them any more
- Skip and destroy a CB whose DMA/IOMMU setup fails; defer on
  -EPROBE_DEFER
- Drop extra of_node_put() in fastrpc_cb_devices_create()
- Link to v6: https://lore.kernel.org/r/20261021-dup-sessions-v6-0-578ab52ba66c@xxxxxxxxxxxxxxxx

Changes in v6:
- Drop unused dev_set_drvdata() from fastrpc_cb_init()
- Use device_for_each_child_reverse() to destroy CB devices
- Return -ENODEV when of_platform_device_create() fails
- Add a comment for FASTRPC_DUP_SESSIONS
- Link to v5: https://lore.kernel.org/r/20260923-dup-sessions-v5-0-e953133a1827@xxxxxxxxxxxxxxxx

Changes in v5:
- Introduce fastrpc_cb_devices_create() and fastrpc_cb_devices_destroy()
  for symmetric CB device lifecycle management in probe and remove.
- Replace module_init/exit pair with module_rpmsg_driver().
- Link to v4: https://lore.kernel.org/r/20260826-dup-sessions-v4-0-35555d2bfed4@xxxxxxxxxxxxxxxx

Changes in v4:
- Rebased on latest linux-next (a8406e6c0b79, 2026-08-25)
- Link to v3: https://lore.kernel.org/r/20260824-dup-sessions-v3-0-4b019def4e0b@xxxxxxxxxxxxxxxx

Changes in v3:
- Add patch to fix async probe race with of_platform_populate().
- Rename fastrpc_cb_probe() to fastrpc_cb_init().
- Reorder series: sync fix, nsessions, binding.
- Collect Reviewed-by tags.
- Link to v2: https://lore.kernel.org/r/20260708-dup-sessions-v2-0-da40f9c98a2b@xxxxxxxxxxxxxxxx

Changes in v2:
- Added patch to deprecate the qcom,nsessions dt-binding.
- Kept the logic unchanged; only split into two patches.
- Link to v1: https://lore.kernel.org/r/20260609-dup-sessions-v1-1-26934abb9fa3@xxxxxxxxxxxxxxxx

---
Vinayak Katoch (3):
      misc: fastrpc: iterate CB nodes manually instead of of_platform_populate
      misc: fastrpc: move ADSP duplicate session creation to the driver
      dt-bindings: misc: qcom,fastrpc: deprecate qcom,nsessions

 .../devicetree/bindings/misc/qcom,fastrpc.yaml     |   2 +
 drivers/misc/fastrpc.c                             | 153 ++++++++++++---------
 2 files changed, 89 insertions(+), 66 deletions(-)
---
base-commit: 7649ba73f9e7e1e04d0b46213e39c79ae09dd55c
change-id: 20260609-dup-sessions-ea2acaac1994

Best regards,
-- 
Vinayak Katoch <vinayak.katoch@xxxxxxxxxxxxxxxx>