linux-kernel - Re: [PATCH v7 08/16] firmware: arm_scmi: Add sync_cmds_atomic

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Message-ID: <20211213115437.23ecitnqztx5yl7g@bogus>
Date:   Mon, 13 Dec 2021 11:54:37 +0000
From:   Sudeep Holla <sudeep.holla@....com>
To:     Cristian Marussi <cristian.marussi@....com>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        james.quinlan@...adcom.com, Jonathan.Cameron@...wei.com,
        f.fainelli@...il.com, etienne.carriere@...aro.org,
        vincent.guittot@...aro.org, souvik.chakravarty@....com
Subject: Re: [PATCH v7 08/16] firmware: arm_scmi: Add
 sync_cmds_atomic_replies transport flag

On Mon, Nov 29, 2021 at 07:11:48PM +0000, Cristian Marussi wrote:
> Add a flag to let the transport signal to the core if its handling of sync
> command implies that, after .send_message has returned successfully, the
> requested command can be assumed to be fully and completely executed on
> SCMI platform side so that any possible response value is already
> immediately available to be retrieved by a .fetch_response: in other words
> the polling phase can be skipped in such a case and the response values
> accessed straight away.
> 
> Note that all of the above applies only when polling mode of operation was
> selected by the core: if instead a completion IRQ was found to be available
> the normal response processing path based on completions will still be
> followed.
> 
> Signed-off-by: Cristian Marussi <cristian.marussi@....com>
> ---
> v5 --> v6
> - added polling_capable helper flag
> v4 --> v5
> - removed RFC tag
> - consider sync_cmds_atomic_replies flag when deciding if polling is to be
>   supported and .poll_done() is not provided.
> - reviewed commit message
> ---
>  drivers/firmware/arm_scmi/common.h |  8 ++++++
>  drivers/firmware/arm_scmi/driver.c | 43 +++++++++++++++++++++++-------
>  2 files changed, 41 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/firmware/arm_scmi/common.h b/drivers/firmware/arm_scmi/common.h
> index 99b74f4d39b6..bf25f0e89c78 100644
> --- a/drivers/firmware/arm_scmi/common.h
> +++ b/drivers/firmware/arm_scmi/common.h
> @@ -412,6 +412,13 @@ struct scmi_device *scmi_child_dev_find(struct device *parent,
>   * @max_msg_size: Maximum size of data per message that can be handled.
>   * @force_polling: Flag to force this whole transport to use SCMI core polling
>   *		   mechanism instead of completion interrupts even if available.
> + * @sync_cmds_atomic_replies: Flag to indicate that the transport assures
> + *			      synchronous-command messages are atomically
> + *			      completed on .send_message: no need to poll
> + *			      actively waiting for a response.

Not sure if atomic is right term to use. It is atomic w.r.t OSPM though.
Can we just say sync_cmd_complete_on_ret or something similar.

-- 
Regards,
Sudeep