[PATCH v3 0/9] Qualcomm Sahara protocol enhancements.

[Kishore Batta]

Hi All,

This series reworks the Sahara protocol driver to make it reusable for
multiple MHI based devices and adds support for capturing, restoring and
exposing DDR training data using the Sahara command mode.

The Sahara protocol is transported over the MHI bus and is used by multiple
flashless devices to transfer firmware images, retrieve memory dumps and
exchange command mode data during early boot. However, the current
implementation lives under the QAIC accelerator driver and contains
device-specific assumptions that limit reuse.

Some MHI devices (for example, QDU100) expose the sahara protocol directly
on a "SAHARA" MHI channel and rely on command mode to exchange DDR training
data with the host. The existing driver does not bind to such devices and
ignores Sahara command mode packets, causing training data to be dropped.

This series addresses these issues by relocating the Sahara driver to the
MHI subsystem, centralizing device specific configuration and adding command
mode handling for DDR training data.

Overview of the changes in this series -
1. Move Sahara under the MHI subsystem:
   a. Relocate the sahara protocol driver from QAIC accelerator tree to
      drivers/bus/mhi.
   b. Register Sahara as an independent MHI protocol driver.

2. Generalize device matching and configuration
   a. Allow the driver to bind to devices exposing the protocol on a
      SAHARA MHI channel.
   b. Centralize firmware image table selection at probe time using a variant
      table, instead of scattered conditionals.
   c. Preserve existing behavior on AIC devices.

3. Add QDU100 firmware image table support
   a. Add a QDU100 image table and select it based on the matched MHI channel.
   b. No separate client driver or registration mechanism is required.

4. Add Sahara command mode support for DDR training.
   a. Handle command mode packets(CMD_READY, EXECUTE, EXECUTE_DATA).
   b. Query supported commands and retrieve DDR training data from the device.
   c. Allocate receive buffers based on the reported payload size and copy
      raw data from the MHI DL.
   d. Store training data in controller-scoped memory using devres so it
      survives sahara channel teardown.

5. Expose DDR training data to userspace
   a. Add a read-only binary sysfs attribute under the MHI controller device.
   b. The attribute reads directly from controller-scoped storage and remains
      available after the Sahara channel device is removed.
   c. Cleanup is handled automatically via device-managed resources.

6. Document the sysfs ABI
   a. Add ABI documentation describing the DDR training data sysfs node.

Signed-off-by: Kishore Batta <kishore.batta@xxxxxxxxxxxxxxxx>
---
Changes in v3:
- Dropped the explicit image table entry for the boot critical image ID and
  added a generic image ID based firmware lookup fallback.
- Link to v2: https://lore.kernel.org/r/20260307-sahara_protocol_new_v2-v2-0-29dc748b5e9c@xxxxxxxxxxxxxxxx

Changes in v2:
- Rebased onto latest linux-next tip.
- Reworked commit messages to clearly start with the problem being solved and
  end with a technical description of the change.
- Moved the Sahara driver to drivers/bus/mhi instead of drivers/soc/qcom,
  reflecting that its an MHI protocol driver rather than a SoC specific driver.
- Removed client side image table registration and consolidated firmware
  selection directly in the sahara driver using a probe-time variant
  mechanism.
- Ensured each patch is self-contained and does not break the build or runtime
  behavior at any intermediate point.
- Simplified state handling and lifetime management to avoid duplicated state
  tracking and ad-hoc cleanup.
- Updated sysfs handling to use controller-scoped devres and avoid one-shot
  reads or manual teardown.
- Link to v1: https://lore.kernel.org/r/20250825101926.2160554-1-kishore.batta@xxxxxxxxxxxxxxxx

---
Kishore Batta (9):
      Add documentation for Sahara protocol.
      bus: mhi: Move sahara protocol driver under drivers/bus/mhi
      bus: mhi: Match devices exposing the protocol on the SAHARA channel
      bus: mhi: Centralize firmware image table selection at probe time
      bus: mhi: Add QDU100 variant and image_id firmware fallback
      bus: mhi: Load DDR training data using per-device serial number
      bus: mhi: Capture DDR training data using command mode
      bus: mhi: Expose DDR training data via controller sysfs
      Documentation: ABI: Add sysfs ABI documentation for DDR training data

 .../ABI/testing/sysfs-bus-mhi-ddr_training_data    |   19 +
 Documentation/sahara/index.rst                     |   14 +
 Documentation/sahara/sahara_protocol.rst           | 1241 ++++++++++++++++++++
 drivers/accel/qaic/Kconfig                         |    1 +
 drivers/accel/qaic/Makefile                        |    3 +-
 drivers/accel/qaic/qaic_drv.c                      |   11 +-
 drivers/bus/mhi/Kconfig                            |    1 +
 drivers/bus/mhi/Makefile                           |    3 +
 drivers/bus/mhi/sahara/Kconfig                     |   18 +
 drivers/bus/mhi/sahara/Makefile                    |    2 +
 drivers/{accel/qaic => bus/mhi/sahara}/sahara.c    |  601 +++++++++-
 {drivers/accel/qaic => include/linux}/sahara.h     |    0
 12 files changed, 1869 insertions(+), 45 deletions(-)
---
base-commit: a0ae2a256046c0c5d3778d1a194ff2e171f16e5f
change-id: 20260307-sahara_protocol_new_v2-662854773cf7

Best regards,
-- 
Kishore Batta <kishore.batta@xxxxxxxxxxxxxxxx>