linux-kernel - Re: [PATCH v2 2/2] firmware: arm_scmi: Augment SMC/HVC to allow optional interrupt

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Date:   Fri, 13 Nov 2020 14:36:27 +0000
From:   Sudeep Holla <sudeep.holla@....com>
To:     Jim Quinlan <james.quinlan@...adcom.com>
Cc:     "maintainer:BROADCOM BCM7XXX ARM ARCHITECTURE" 
        <bcm-kernel-feedback-list@...adcom.com>,
        Cristian Marussi <cristian.marussi@....com>,
        Sudeep Holla <sudeep.holla@....com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/2] firmware: arm_scmi: Augment SMC/HVC to allow
 optional interrupt

On Fri, Nov 13, 2020 at 09:26:43AM -0500, Jim Quinlan wrote:
> Hi, these are fast calls.  Regards, Jim
> 
> 
> On Fri, Nov 13, 2020 at 4:47 AM Sudeep Holla <sudeep.holla@....com> wrote:
> >
> > On Thu, Nov 12, 2020 at 12:56:27PM -0500, Jim Quinlan wrote:
> > > The SMC/HVC SCMI transport is modified to allow the completion of an SCMI
> > > message to be indicated by an interrupt rather than the return of the smc
> > > call.  This accommodates the existing behavior of the BrcmSTB SCMI
> > > "platform" whose SW is already out in the field and cannot be changed.
> > >
> >
> > Sorry for missing to check with you earlier. Are these not fast smc calls ?
> > Can we check the SMC Function IDs for the same and expect IRQ to be present
> > if they are not fast calls ?
> Hi, if I understand you correctly you want to do something like this:
>
>  if (! ARM_SMCCC_IS_FAST_CALL(func_id)) {
>         /* look for irq and request it */
> }
>

Yes.

> But we  do use fast calls.

What was the rationale for retaining fast SMC calls but use IRQ for Tx
completion ?

Is it because you offload it to some other microprocessor and don't
continue execution on secure side in whcih case you can afford fast call ?

--
Regards,
Sudeep