linux-kernel - Re: [PATCH V2 1/2] opp: Allow dev_pm_opp_get_opp_table() to return -EPROBE

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Message-ID: <20201020095935.2ttoked5tozvcr24@vireshk-i7>
Date:   Tue, 20 Oct 2020 15:29:35 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     ulf.hansson@...aro.org, "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Kevin Hilman <khilman@...nel.org>, Pavel Machek <pavel@....cz>,
        Len Brown <len.brown@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Viresh Kumar <vireshk@...nel.org>, Nishanth Menon <nm@...com>,
        Stephen Boyd <sboyd@...nel.org>, Kukjin Kim <kgene@...nel.org>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        linux-pm@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>, nks@...wful.org,
        georgi.djakov@...aro.org, Stephan Gerhold <stephan@...hold.net>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org
Subject: Re: [PATCH V2 1/2] opp: Allow dev_pm_opp_get_opp_table() to return
 -EPROBE_DEFER

On 20-10-20, 10:52, Sudeep Holla wrote:
> On Tue, Oct 20, 2020 at 03:11:34PM +0530, Viresh Kumar wrote:
> > On 20-10-20, 10:37, Sudeep Holla wrote:
> > > On Tue, Oct 20, 2020 at 11:24:32AM +0530, Viresh Kumar wrote:
> > > > On 20-10-20, 10:35, Viresh Kumar wrote:
> > > > > On 19-10-20, 15:10, Sudeep Holla wrote:
> > > > > > On Mon, Oct 19, 2020 at 04:05:35PM +0530, Viresh Kumar wrote:
> > > > > > > On 19-10-20, 11:12, Sudeep Holla wrote:
> > > > > > > > Yes it has clocks property but used by SCMI(for CPUFreq/DevFreq) and not
> > > > > > > > by any clock provider driver. E.g. the issue you will see if "clocks"
> > > > > > > > property is used instead of "qcom,freq-domain" on Qcom parts.
> > > > > > > 
> > > > > > > Okay, I understand. But what I still don't understand is why it fails
> > > > > > > for you. You have a clocks property in DT for the CPU, the OPP core
> > > > > > > tries to get it and will get deferred-probed, which will try probing
> > > > > > > at a later point of time and it shall work then. Isn't it ?
> > > > > > >
> > > > > > 
> > > > > > Nope unfortunately. We don't have clock provider, so clk_get will
> > > > > > never succeed and always return -EPROBE_DEFER.
> > > > > 
> > > > > Now this is really bad, you have a fake clocks property, how is the
> > > > > OPP core supposed to know it ? Damn.
> > > > 
> > > > What about instead of fixing the OPP core, which really is doing the
> > > > right thing, we fix your driver (as you can't fix the DT) and add a
> > > > dummy CPU clk to make it all work ?
> > > >
> > > 
> > > I really would avoid that. I would rather change the binding as there is
> > > no single official users of that binding in the upstream tree.
> > 
> > But how will you solve backward compatibility thing then ?
> > 
> 
> I am just betting on the fact that no users upstream means no backward
> compatibility needed. If someone raises issue we need to add backward
> compatibility with dummy clk as you suggested.

Okay. I would have done a change in the OPP core to fix the issue, but
the current code looks correct and we shouldn't change it to satisfy
buggy users. I hope that makes sense.

-- 
viresh