linux-kernel - Re: [PATCH 4/5] firmware: arm_scmi: smc transport supports multi-message pool

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Message-ID: <CAN5uoS8tz0wXkD1dtFbAYBWHvngHG8KeUD2JkK32siPa2MwgYA@mail.gmail.com>
Date:   Fri, 9 Oct 2020 14:43:31 +0200
From:   Etienne Carriere <etienne.carriere@...aro.org>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     linux-kernel@...r.kernel.org,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        Cristian Marussi <cristian.marussi@....com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Souvik Chakravarty <Souvik.Chakravarty@....com>,
        Peng Fan <peng.fan@....com>
Subject: Re: [PATCH 4/5] firmware: arm_scmi: smc transport supports
 multi-message pool

On Thu, 8 Oct 2020 at 23:11, Sudeep Holla <sudeep.holla@....com> wrote:
>
> On Thu, Oct 08, 2020 at 04:37:21PM +0200, Etienne Carriere wrote:
> > There is no reason for the smc transport to restrict itself to a 1
> > message pool. More can be allocated, messages are copied from/to the
> > shared memory only on SMC exit/entry hence SCMI driver can play with
> > several messages.
> >
> > Use value of 20 to mimic mailbox transport implementation.
>
> What is the need to mimic ?

I had to pick a value. I can't say whether 2, 5 or 20 is better.
I looks how the mailbox transport did and used the same value
as it seemed reasonable regarding its memory cost.

>
> > Any high value could fit. This should be something configurable.
>
> Why not 10 or 100 ? I see any value other than 1 is useless as we lock
> the channel in send_message and we don't maintain a queue like mailbox.

I'll check again.
Playing with SCMI voltage domain [1], it happens that I needed several
preallocated
message buffers unless what regulators fail to be probed.

[1] https://lkml.org/lkml/2020/10/5/1341

Regards,
etienne

>
> --
> Regards,
> Sudeep