linux-kernel - Re: [RFC PATCH 01/10] firmware: arm_scmi: Reset properly xfer SCMI status

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Message-ID: <20210607182754.3wsmhc2t5mh36ycm@bogus>
Date:   Mon, 7 Jun 2021 19:27:54 +0100
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: [RFC PATCH 01/10] firmware: arm_scmi: Reset properly xfer SCMI
 status

On Mon, Jun 07, 2021 at 07:01:37PM +0100, Cristian Marussi wrote:
> On Mon, Jun 07, 2021 at 06:38:09PM +0100, Sudeep Holla wrote:
> > On Sun, Jun 06, 2021 at 11:12:23PM +0100, Cristian Marussi wrote:
> > > When an SCMI command transfer fails due to some protocol issue an SCMI
> > > error code is reported inside the SCMI message payload itself and it is
> > > then retrieved and transcribed by the specific transport layer into the
> > > xfer.hdr.status field by transport specific .fetch_response().
> > >
> > > The core SCMI transport layer never explicitly reset xfer.hdr.status,
> > > so when an xfer is reused, if a transport misbehaved in handling such
> > > status field, we risk to see an invalid ghost error code.
> > >
> > > Reset xfer.hdr.status to SCMI_SUCCESS right before each transfer is
> > > started.
> > >
> >
> > Any particular reason why it can't be part of xfer_get_init which has other
> > initialisations ? If none, please move it there.
> >
>
> Well it was there initially then I moved it here.
>
> The reason is mostly the same as the reason for the other patch in this
> series that adds a reinit_completion() in this same point: the core does
> not forbid to reuse an xfer multiple times, once obtained with xfer_get()
> or xfer_get_init(), and indeed some protocols do such a thing: they
> implements such do_xfer looping and bails out on error.
>

Makes sense. But it is okay to retain xfer->transfer_id for every transfer
in such a loop ?

> In the way that it is implemented now in protocols poses no problem
> indeed because the do_xfer loop bails out on error and the xfer is put,
> but as soon as some protocol is implemented that violates this common
> practice and it just keeps on reuse an xfer after an error fo other
> do_xfers() this breaks...so it seemed more defensive to just reinit the
> completion and the status before each send.

Fair enough. But they use it to send same message I guess, may be if it
gave error or something ? I would like to really know such a sequence
instead of assisting that 😉. 

--
Regards,
Sudeep