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

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Message-ID: <CA+-6iNz099CQQky7U7vm7w7s=QAECauuosLAf7zC4hWNFZ9yqQ@mail.gmail.com>
Date:   Fri, 13 Nov 2020 10:12:24 -0500
From:   Jim Quinlan <james.quinlan@...adcom.com>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     "maintainer:BROADCOM BCM7XXX ARM ARCHITECTURE" 
        <bcm-kernel-feedback-list@...adcom.com>,
        Cristian Marussi <cristian.marussi@....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 9:36 AM Sudeep Holla <sudeep.holla@....com> wrote:
>
> 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 ?

Hi Sudeep,
I have an answer for this but allow me time to contact the platform FW
engineer to make sure I have the full picture -- this may take a day
or two.  Regardless, our implementation has already "shipped" to
customers for some time so we may not be able to change it.
Regards, Jim
>
>
> --
> Regards,
> Sudeep

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