Re: [PATCH v6 1/7] Add documentation for Sahara protocol

[Kishore Batta <kishore.batta@oss.qualcomm.com>]

On 7/8/2026 10:16 AM, Randy Dunlap wrote:
> On 7/1/26 3:37 AM, Kishore Batta wrote:
>> +The packet flow sequence is as follows :
>> +
>> +1. The target sends the hello packet to the host to initiate the protocol
>> +   with the mode set to image transfer pending.
>> +
>> +2. The host sends a hello response packet with a success status and sets the
>> +   mode to image transfer pending after it receives the hello packet and
>> +   validates the protocol version running on the target.
>> +
>> +3. After the target receives the hello response, it initiates the data
>> +   transfer by requesting the size of DDR training/calibration data.
>> +
>> +4. The host sends back the DDR training/calibration data to the target.
>> +
>> +5. The target decodes the training data and does not find valid DDR
>> +   calibration data, target sends END_IMAGE_TX to interrupt the transfer.
>> +
>> +6. The host sends DONE after receives END_IMAGE_TX.
>> +
>> +7. The target sends DONE_RESP with mode = IMAGE_TX_PENDING because it has
>> +   not received all images.
>> +
>> +8. The target executes DDR training process to generate valid DDR calibration
>> +   data and prepares to push back to host.
>> +
>> +9. The target initiates protocol by sending a hello packet with COMMAND_MODE
>> +   to the host.
>> +
>> +10. The host sends a hello response packet with a success status and sets the
>> +    mode to COMMAND_MODE.
>> +
>> +11. The target sends CMD_READY to the host.
>> +
>> +12. The host receives CMD_READY and starts to get command IDs to be executed.
>> +
>> +13. The target sends CMD_ID = 9 to push DDR calibration data to host.
>> +
>> +14. The host executes CMD_ID = 9 to get DDR calibration data from the target.
>> +
>> +15. The target sends RAW_DATA with the payload which contains DDR calibration
>> +    data to host.
>> +
>> +16. The host saves training data in the kernel buffer and exposes to userspace
>> +    via the sysfs entry. The host sends CMD_SWITCH_MODE with the mode set to
>> +    IMAGE_TX_PENDING to continue booting.
>> +
>> +17. After the target receives the CMD_SWITCH_MODE command, it sends HELLO to
>> +    the host with the mode set to IMAGE_TX_PENDING. The target and the host
>> +    repeat the packet flow for image transfer to get all booting-required
>> +    images.
>> +
>> +18. Upon successful transfer of all images, the target sends an END_IMAGE_TX
>> +    packet with a success status to the host.
>> +
>> +19. The host sends DONE after it receives END_IMAGE_TX.
>> +
>> +20. The target sends DONE_RESP with the mode set to IMAGE_TX_COMPLETE because
>> +    it has received all images. The process has been completed after the host
>> +    receives DONE_RESP with the mode set to IMAGE_TX_COMPLETE.
>> +
>> +Subsequent boot scenario with valid DDR calibration data
>> +--------------------------------------------------------
>> +
>> +The below firgure shows the subsequent boot scenario with valid DDR calibration
>> +data process being loaded from host to target.
>> +
>> +.. code-block:: text
>> +
>> +                        Host                       Target
>> +                          |          HELLO            |
>> +                          |   (mode = image transfer) |
>> +                          |<--------------------------|
>> +                          |                           |
>> +                          |         HELLO RESP        |
>> +                          |   (mode = image transfer) |
>> +                          |-------------------------->|
>> +                          |                           |
>> +                          |         READ_DATA         |
>> +                          |   (img ID:34, 0, offset,  |
>> +                          | size of DDR training data)|
>> +                          |<--------------------------|
>> +                          |                           |
>> +                          |         RAW_DATA          |
>> +                          |(size of DDR training data)|
>> +                          |-------------------------->|
>> +                          |                           |
>> +                          |                           |
>> +                          |       END_IMAGE_TX        |
>> +                          |<--------------------------|
>> +                          |                           |
>> +                          |                           |
>> +                          |          DONE             |
>> +                          |-------------------------->|
>> +                          |                           |
>> +                          |                           |
>> +                          |         DONE_RESP         |
>> +                          | (mode = IMAGE_TX_PENDING) |
>> +                          |<--------------------------|
>> +                          |                           |
>> +                          | Subsequent boot scenario  |
>> +                          | (valid calibration data)  |
>> +                          | DDR driver configures DDR |
>> +                          | using valid calibration   |
>> +                          | data                      |
>> +                          |                           |
>> +                          |                           |
>> +                          |          HELLO            |
>> +                          | (mode = IMAGE_TX_PENDING) |
>> +                          |<--------------------------|
>> +                          |                           |
>> +                          |         HELLO RESP        |
>> +                          | (mode = IMAGE_TX_PENDING) |
>> +                          |-------------------------->|
>> +                          |                           |
>> +                          | Boot/Load rest of the     |
>> +                          |    images....             |
>> +                          |                           |
>> +                          |       END_IMAGE_TX        |
>> +                          |<--------------------------|
>> +                          |                           |
>> +                          |                           |
>> +                          |          DONE             |
>> +                          |-------------------------->|
>> +                          |                           |
>> +                          |                           |
>> +                          |         DONE_RESP         |
>> +                          |(mode = IMAGE_TX_COMPLETE) |
>> +                          |<--------------------------|
>> +                          |                           |
>> +
>> +The packet flow is as follows :
>> +
> s/as follows :/as follows:/
> in 2 places.


ACK. I'll remove the extra space before the colon in both places in the 
next version.


>
>> +1. The target sends the hello packet to the host to initiate the protocol
>> +   with the mode set to image transfer pending.