linux-kernel - Re: [PATCH v6 05/17] firmware: arm_scmi: Add transport optional init/exit support

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Message-ID: <20210728122837.GG6592@e120937-lin>
Date:   Wed, 28 Jul 2021 13:28:37 +0100
From:   Cristian Marussi <cristian.marussi@....com>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        virtualization@...ts.linux-foundation.org,
        virtio-dev@...ts.oasis-open.org, james.quinlan@...adcom.com,
        Jonathan.Cameron@...wei.com, f.fainelli@...il.com,
        etienne.carriere@...aro.org, vincent.guittot@...aro.org,
        souvik.chakravarty@....com, igor.skalkin@...nsynergy.com,
        peter.hilber@...nsynergy.com, alex.bennee@...aro.org,
        jean-philippe@...aro.org, mikhail.golubev@...nsynergy.com,
        anton.yakovlev@...nsynergy.com, Vasyl.Vavrychuk@...nsynergy.com,
        Andriy.Tryshnivskyy@...nsynergy.com
Subject: Re: [PATCH v6 05/17] firmware: arm_scmi: Add transport optional
 init/exit support

On Wed, Jul 28, 2021 at 12:40:18PM +0100, Sudeep Holla wrote:
> On Mon, Jul 12, 2021 at 03:18:21PM +0100, Cristian Marussi wrote:
> > Some SCMI transport could need to perform some transport specific setup
> > before they can be used by the SCMI core transport layer: typically this
> > early setup consists in registering with some other kernel subsystem.
> > 
> > Add the optional capability for a transport to provide a couple of .init
> > and .exit functions that are assured to be called early during the SCMI
> > core initialization phase, well before the SCMI core probing step.
> > 
> > [ Peter: Adapted RFC patch by Cristian for submission to upstream. ]
> > Signed-off-by: Peter Hilber <peter.hilber@...nsynergy.com>
> > [ Cristian: Fixed scmi_transports_exit point of invocation ]
> > Signed-off-by: Cristian Marussi <cristian.marussi@....com>
> > ---
> > v4 --> V5
> > - removed useless pr_debug
> > - moved scmi_transport_exit() invocation
> > ---

Hi Sudeep,

thanks for having a look.

> >  drivers/firmware/arm_scmi/common.h |  8 +++++
> >  drivers/firmware/arm_scmi/driver.c | 56 ++++++++++++++++++++++++++++++
> >  2 files changed, 64 insertions(+)
> > 
> > diff --git a/drivers/firmware/arm_scmi/common.h b/drivers/firmware/arm_scmi/common.h
> > index 7c2b9fd7e929..6bb734e0e3ac 100644
> > --- a/drivers/firmware/arm_scmi/common.h
> > +++ b/drivers/firmware/arm_scmi/common.h
> > @@ -321,6 +321,12 @@ struct scmi_device *scmi_child_dev_find(struct device *parent,
> >  /**
> >   * struct scmi_desc - Description of SoC integration
> >   *
> > + * @init: An optional function that a transport can provide to initialize some
> > + *	  transport-specific setup during SCMI core initialization, so ahead of
> > + *	  SCMI core probing.
> > + * @exit: An optional function that a transport can provide to de-initialize
> > + *	  some transport-specific setup during SCMI core de-initialization, so
> > + *	  after SCMI core removal.
> >   * @ops: Pointer to the transport specific ops structure
> >   * @max_rx_timeout_ms: Timeout for communication with SoC (in Milliseconds)
> >   * @max_msg: Maximum number of messages that can be pending
> > @@ -328,6 +334,8 @@ struct scmi_device *scmi_child_dev_find(struct device *parent,
> >   * @max_msg_size: Maximum size of data per message that can be handled.
> >   */
> >  struct scmi_desc {
> > +	int (*init)(void);
> > +	void (*exit)(void);
> 
> Does it make sense to rename scmi_desc as scmi_transport or scmi_transport_desc ?
> I reason I ask is plain init/exit here doesn't make sense. You can change it
> to transport_init/exit if we don't want to rename the structure.
> 

Yes indeed I'll rename these to transport_init/exit in V7.

> >  	const struct scmi_transport_ops *ops;
> 
> I assume we don't want init/exit inside ops as it is shared with protocols ?
> Looks good other than the above comment.
> 

It seemed to me that scmi_transport_ops were more related to an initialized
instance of a transport and as such used when the scmi instance is probed or
later, while these transport_init/exit are more general transport specific
methods that have to be called, if provided, at scmi driver init, way before
scmi_probe(), to allow for early transport inits, as an example virtio-scmi
uses these to register at first with the virtio subsystem; so I kept them
separated.

Thanks,
Cristian