linux-kernel - Re: [PATCH 0/6] mailbox: pcc: Refactor and improve initialisation and interrupt handling

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Message-ID: <8a7aa313-568b-4ee8-a575-4a62933eb289@amperemail.onmicrosoft.com>
Date: Fri, 17 Oct 2025 12:49:54 -0400
From: Adam Young <admiyo@...eremail.onmicrosoft.com>
To: Sudeep Holla <sudeep.holla@....com>, linux-acpi@...r.kernel.org,
 linux-kernel@...r.kernel.org
Cc: Adam Young <admiyo@...amperecomputing.com>,
 Robbie King <robbiek@...ghtlabs.com>, Huisong Li <lihuisong@...wei.com>,
 Jassi Brar <jassisinghbrar@...il.com>,
 Cristian Marussi <cristian.marussi@....com>
Subject: Re: [PATCH 0/6] mailbox: pcc: Refactor and improve initialisation and
 interrupt handling

Tested-by: Adam Young <admiyo@...amperecompuitng.com>

On 10/16/25 15:08, Sudeep Holla wrote:
> This series refines and stabilizes the PCC mailbox driver to improve
> initialisation order, interrupt handling, and completion signaling.
>
> It begins by reverting a previous patch that introduced redundant shared
> buffer management, simplifying the driver and restoring consistency with the
> mailbox core framework. It is essential to have a proper baseline for the
> main changes in the series.
>
> Subsequent patches add proper completion reporting, clarify completion mode
> selection, and fix subtle sequencing and interrupt issues to ensure
> predictable, robust operation across ACPI-based PCC implementations.
>
> Specifically, the series:
>
> 1. Removes redundant shared buffer logic, reverting an earlier change that
>     duplicated existing mailbox core features and caused maintenance overhead.
>
> 2. Adds ->last_tx_done() support to allow polling clients to verify
>     transmission completion without relying on interrupts.
>
> 3. Explicitly configures completion modes (txdone_irq or txdone_poll) based
>     on ACPI PCCT doorbell capability flag, ensuring the correct completion
>     mechanism is chosen for each platform.
>
> 4. Marks transmit completion in the IRQ handler by invoking mbox_chan_txdone(),
>     preventing timeouts and ensuring proper synchronization for interrupt-driven
>     transfers.
>
> 5. Initializes the shared memory region (SHMEM) before binding clients,
>     preventing race conditions where clients could access uninitialized memory.
>
> 6. Clears any pending responder interrupts before enabling IRQs, avoiding
>     spurious or false interrupts during startup.
>
> Together, these updates make the PCC mailbox driver cleaner, more reliable,
> and fully aligned with the mailbox framework's expectations, improving
> determinism and robustness across different hardware platforms.
>
> Signed-off-by: Sudeep Holla <sudeep.holla@....com>
> ---
> Sudeep Holla (6):
>        Revert "mailbox/pcc: support mailbox management of the shared buffer"
>        mailbox: pcc: Wire up ->last_tx_done() for PCC channels
>        mailbox: pcc: Set txdone_irq/txdone_poll based on PCCT flags
>        mailbox: pcc: Mark Tx as complete in PCC IRQ handler
>        mailbox: pcc: Initialize SHMEM before binding the channel with the client
>        mailbox: pcc: Clear any pending responder interrupts before enabling it
>
>   drivers/mailbox/pcc.c | 118 ++++++++++----------------------------------------
>   include/acpi/pcc.h    |  29 -------------
>   2 files changed, 23 insertions(+), 124 deletions(-)
> ---
> base-commit: 7ea30958b3054f5e488fa0b33c352723f7ab3a2a
> change-id: 20251016-pcc_mb_updates-d9d428985400
>
>