linux-kernel - Re: [PATCH v3 2/3] opp/of: Allow empty opp-table with opp-shared

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Message-ID: <fead451e-329b-465c-5055-f5dadd58e056@arm.com>
Date:   Mon, 16 Nov 2020 11:45:31 +0000
From:   Nicola Mazzucato <nicola.mazzucato@....com>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-pm@...r.kernel.org, devicetree@...r.kernel.org,
        sudeep.holla@....com, rjw@...ysocki.net, vireshk@...nel.org,
        robh+dt@...nel.org, sboyd@...nel.org, nm@...com,
        daniel.lezcano@...aro.org, morten.rasmussen@....com,
        chris.redpath@....com
Subject: Re: [PATCH v3 2/3] opp/of: Allow empty opp-table with opp-shared

Hi Viresh,

sorry for being late in replying.


On 11/5/20 4:41 AM, Viresh Kumar wrote:
> On 04-11-20, 17:54, Nicola Mazzucato wrote:
>> Initially I thought to place a comment right there but I ended up with an
>> explanation of this case at the top of this function (the corner-case). It
>> probably also needs more details..
> 
> I read it earlier as well but yeah, that wasn't good enough for me to
> understand what you are doing.
> 
>> Basically, on this case - empty opp table & opp-shared - we limit the scope of
>> opp-shared to *only* tell us about hw description, and not marking the opp
>> points as shared, since they are not present in DT.
> 
> It doesn't matter where the OPP table entries are coming from. The OPP
> table should be marked shared if it is found to be shared.
> 
>> It would be the equivalent
>> of describing that devices share clock/voltage lines, but we can't tell anything
>> about opp points cause they are not there (in DT).
> 
> Its okay, even then we should set the right flags here. It is really
> confusing that we blindly set it as exclusive, even though it may be
> shared.
> 
>> OTOH If we don't set shared_opp to OPP_TABLE_ACCESS_EXCLUSIVE for that specific
>> case, we won't be able to add opps for the remaining cpus as the opp core
>> will find the opps as duplicated. This is a corner case, really.
> 
> Hmm, I am not sure where you fail and how but this should be set to
> OPP_TABLE_ACCESS_EXCLUSIVE only if the OPP table isn't shared. else it
> should be OPP_TABLE_ACCESS_SHARED.
> 
Thanks for providing more details around the meaning of opp-shared, much
appreciated. I had some time to play a bit more, and yes, there is no need to
set shared_opp to OPP_TABLE_ACCESS_EXCLUSIVE. A minimal change in the driver
sequence would suffice.

I will remove that in the V4.

Many thanks,
Nicola