Re: [PATCH v2 02/13] mailbox: pcc: Always clear the platform ack interrupt first

lihuisong (C)
2025-03-11T11:19:24Z

在 2025/3/6 0:38, Sudeep Holla 写道:
> The PCC mailbox interrupt handler (pcc_mbox_irq()) currently checks
> for command completion flags and any error status before clearing the
> interrupt.
>
> The below sequence highlights an issue in the handling of PCC mailbox
> interrupts, specifically when dealing with doorbell notifications and
> acknowledgment between the OSPM and the platform where type3 and type4
> channels are sharing the interrupt.
>
> -------------------------------------------------------------------------
> | T | Platform Firmware | OSPM/Linux PCC driver |
> |---|---------------------------------|---------------------------------|
> | 1 | | Build message in shmem |
> | 2 | | Ring Type3 chan doorbell |
> | 3 | Receives the doorbell interrupt | |
> | 4 | Process the message from OSPM | |
> | 5 | Build response for the message | |
> | 6 | Ring Platform ACK interrupt on | |
> | | Type3 chan to OSPM | Received the interrupt |
> | 7 | Build Notification in Type4 Chan| |
> | 8 | | Start processing interrupt in |
> | | | pcc_mbox_irq() handler |
> | 9 | | Enter PCC handler for Type4 chan|
> |10 | | Check command complete cleared |
> |11 | | Read the notification |
> |12 | | Clear Platform ACK interrupt |
> | | No effect from the previous step yet as the Platform ACK |
> | | interrupt has not yet been triggered for this channel |
> |13 | Ring Platform ACK interrupt on | |
> | | Type4 chan to OSPM | |
> |14 | | Enter PCC handler for Type3 chan|
> |15 | | Command complete is set. |
> |16 | | Read the response. |
> |17 | | Clear Platform ACK interrupt |
> |18 | | Leave PCC handler for Type3 |
> |19 | | Leave pcc_mbox_irq() handler |
> |20 | | Re-enter pcc_mbox_irq() handler |
> |21 | | Enter PCC handler for Type4 chan|
> |22 | | Leave PCC handler for Type4 chan|
> |23 | | Enter PCC handler for Type3 chan|
> |24 | | Leave PCC handler for Type3 chan|
> |25 | | Leave pcc_mbox_irq() handler |
> -------------------------------------------------------------------------
>
> The key issue occurs when OSPM tries to acknowledge platform ack
> interrupt for a notification which is ready to be read and processed
> but the interrupt itself is not yet triggered by the platform.
>
> This ineffective acknowledgment leads to an issue later in time where
> the interrupt remains pending as we exit the interrupt handler without
> clearing the platform ack interrupt as there is no pending response or
> notification. The interrupt acknowledgment order is incorrect.
>
> To resolve this issue, the platform acknowledgment interrupt should
> always be cleared before processing the interrupt for any notifications
> or response.
>
> Reported-by: Robbie King <robbiek@xsightlabs.com>
> Reviewed-by: Huisong Li <lihuisong@huawei.com>
> Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Tested-by: Huisong Li <lihuisong@huawei.com>
>