linux-kernel - Re: [PATCH V3 2/2] base/drivers/arch_topology: Default dmips-mhz if they are not set in DT

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Date:   Mon, 26 Nov 2018 12:15:19 +0000
From:   Quentin Perret <quentin.perret@...aro.org>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:     Viresh Kumar <viresh.kumar@...aro.org>, rjw@...ysocki.net,
        linux-kernel@...r.kernel.org,
        Chris Redpath <chris.redpath@...aro.org>,
        Amit Kucheria <amit.kucheria@...aro.org>,
        Nicolas Dechesne <nicolas.dechesne@...aro.org>,
        Niklas Cassel <niklas.cassel@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>
Subject: Re: [PATCH V3 2/2] base/drivers/arch_topology: Default dmips-mhz if
 they are not set in DT

On Monday 26 Nov 2018 at 12:36:31 (+0100), Daniel Lezcano wrote:
> On 26/11/2018 12:09, Quentin Perret wrote:
> > On Monday 26 Nov 2018 at 15:49:55 (+0530), Viresh Kumar wrote:
> >> On 26-11-18, 11:08, Daniel Lezcano wrote:
> >>> On 26/11/2018 10:52, Quentin Perret wrote:
> >>>> Maybe you want to test 'if (!raw_capacity || cap_parsing_failed)' at the
> >>>> top of topology_parse_cpu_capacity() ?
> >>>
> >>> I prefer to update the documentation, it makes more sense than adding
> >>> more cumbersome tests in the current code.
> >>
> >> +1
> >>
> >> Throwing an error and ignoring DT number completely for the capacity
> >> are good enough in my opinion as well.
> >>
> >> And who cares for the platforms that can't even fill the DT properly :)
> > 
> > Right, I think we all agree the case with a partially filled DT is
> > broken. I don't actually care too much about the behaviour in this case,
> > but it needs to be consistent with the doc.
> > 
> > So, as long as you fix the doc, that change is fine by me :-)
> 
> Ok what about the following change ?
> 
> "
> 
> If capacity-dmips-mhz is not specified or if the parsing fails, the
> default capacity value will be computed against the highest frequency,
> it will result most of the time on the same capacity value.

That "most of the time" sounds a bit odd no ? Maybe mention explicitly
the case you're referring to (that is when all CPUs have the same max
freq) ?

> However on
> some platform with different OPP set but the same micro-architecture,
> the capacity will be scaled down for CPUs having lower frequencies.
> 
> "

Other than that LGTM.

Thanks,
Quentin