linux-kernel - Re: [PATCH 22/22] firmware: arm_scmi: Add SCMIv3.1 PERFORMANCE_LIMITS

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Date:   Thu, 28 Apr 2022 14:52:33 +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,
        Sudeep Holla <sudeep.holla@....com>,
        vincent.guittot@...aro.org, souvik.chakravarty@....com
Subject: Re: [PATCH 22/22] firmware: arm_scmi: Add SCMIv3.1
 PERFORMANCE_LIMITS_SET checks

On Thu, Apr 28, 2022 at 02:49:48PM +0100, Cristian Marussi wrote:
> On Thu, Apr 28, 2022 at 02:13:57PM +0100, Sudeep Holla wrote:
> > On Wed, Mar 30, 2022 at 04:05:51PM +0100, Cristian Marussi wrote:
> > > Starting with SCMIv3.1, the PERFORMANCE_LIMITS_SET command allows a user
> > > to request only one between max and min ranges to be changed, while leaving
> > > the other untouched if set to zero in the request; anyway SCMIv3.1 states
> > > also explicitly that you cannot leave both of those unchanged (zeroed) when
> > > issuing such command: add a proper check for this condition.
> > > 
> > > Signed-off-by: Cristian Marussi <cristian.marussi@....com>
> > > ---
> > >  drivers/firmware/arm_scmi/perf.c | 3 +++
> > >  1 file changed, 3 insertions(+)
> > > 
> > > diff --git a/drivers/firmware/arm_scmi/perf.c b/drivers/firmware/arm_scmi/perf.c
> > > index 65ffda5495d6..8f4051aca220 100644
> > > --- a/drivers/firmware/arm_scmi/perf.c
> > > +++ b/drivers/firmware/arm_scmi/perf.c
> > > @@ -423,6 +423,9 @@ static int scmi_perf_limits_set(const struct scmi_protocol_handle *ph,
> > >  	struct scmi_perf_info *pi = ph->get_priv(ph);
> > >  	struct perf_dom_info *dom = pi->dom_info + domain;
> > >  
> > > +	if (PROTOCOL_REV_MAJOR(pi->version) >= 0x3 && !max_perf && !min_perf)
> > > +		return -EINVAL;
> > > +
> > 
> > Do we really need the version check here ? I agree it was explicitly added
> > in v3.1, but it makes sense on any version really. No ?
> 
> Indeed seemed a silly patch also to me but given that only in v3.1 it is
> explicitly stated that you cannot issue this command with both min and
> max ZEROED I though this could have broken older fw that allowed
> setting PERF_LIMITS_SET max=0 min=0
> 
> ....maybe overthought ...

Hmm, let's keep it unconditional for now. We can add if someone reports
broken firmware. BTW there are no users in the kernel 😄.

-- 
Regards,
Sudeep