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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> Tested-by: Huisong Li <lihuisong@huawei.com> Tested-by: Adam Young <admiyo@os.amperecomputing.com> Tested-by: Robbie King <robbiek@xsightlabs.com> Signed-off-by: Sudeep Holla <sudeep.holla@arm.com> Signed-off-by: Jassi Brar <jassisinghbrar@gmail.com> |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.