On 3/5/2025 11:38 AM, Sudeep Holla wrote: > 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@xxxxxxxxxxxxxx> > Reviewed-by: Huisong Li <lihuisong@xxxxxxxxxx> > Signed-off-by: Sudeep Holla <sudeep.holla@xxxxxxx> Tested-by: Robbie King <robbiek@xxxxxxxxxxxxxx>
