linux-kernel - Re: [PATCH v4 3/8] firmware: arm_scmi: Add atomic mode support to virtio transport

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Message-ID: <20220215091046.GF2535@e120937-lin>
Date:   Tue, 15 Feb 2022 09:11:01 +0000
From:   Cristian Marussi <cristian.marussi@....com>
To:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        mst@...hat.com
Cc:     sudeep.holla@....com, james.quinlan@...adcom.com,
        Jonathan.Cameron@...wei.com, f.fainelli@...il.com,
        etienne.carriere@...aro.org, vincent.guittot@...aro.org,
        souvik.chakravarty@....com, peter.hilber@...nsynergy.com,
        igor.skalkin@...nsynergy.com,
        "Michael S. Tsirkin" <mst@...hat.com>,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v4 3/8] firmware: arm_scmi: Add atomic mode support to
 virtio transport

On Sun, Feb 13, 2022 at 07:58:27PM +0000, Cristian Marussi wrote:
> Add support for .mark_txdone and .poll_done transport operations to SCMI
> VirtIO transport as pre-requisites to enable atomic operations.
> 
> Add a Kernel configuration option to enable SCMI VirtIO transport polling
> and atomic mode for selected SCMI transactions while leaving it default
> disabled.
> 
> Cc: "Michael S. Tsirkin" <mst@...hat.com>
> Cc: Igor Skalkin <igor.skalkin@...nsynergy.com>
> Cc: Peter Hilber <peter.hilber@...nsynergy.com>
> Cc: virtualization@...ts.linux-foundation.org
> Signed-off-by: Cristian Marussi <cristian.marussi@....com>
> ---
> v1 --> v2
> - shrinked spinlocked section within virtio_poll_done to exclude
>   virtqueue_poll
> - removed poll_lock
> - use vio channel refcount acquire/release logic when polling
> - using new free_list accessors
> - added new dedicated pending_lock to access pending_cmds_list
> - fixed a few comments
> 
> v0 --> v1
> - check for deferred_wq existence before queueing work to avoid
>   race at driver removal time
> - changed mark_txdone decision-logic about message release
> - fixed race while checking for msg polled from another thread
> - using dedicated poll_status instead of poll_idx upper bits
> - pick initial poll_idx earlier inside send_message to avoid missing
>   early replies
> - removed F_NOTIFY mention in comment
> - clearing xfer->priv on the IRQ tx path once message has been fetched
> - added some store barriers
> - updated some comments
> ---
>  drivers/firmware/arm_scmi/Kconfig  |  15 ++
>  drivers/firmware/arm_scmi/driver.c |   9 +-
>  drivers/firmware/arm_scmi/virtio.c | 277 ++++++++++++++++++++++++++++-
>  3 files changed, 291 insertions(+), 10 deletions(-)
> 

Hi Michael,

how do you feel about the current status of this patch and the previous
two in this series about SCMI virtio polling support after the last
fixes ?

Could we start thinking about merging this series on the SCMI side, leaving
aside for the next iteration the polling ABA-problem mitigation I proposed
in the virtio core (wrap counters and new API to enable them) that is now
in a distinct series ? (and probably needs more tests/perfs/feedback...)

Thank you,
Cristian