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

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Message-ID: <20201019091723.GA12087@bogus>
Date:   Mon, 19 Oct 2020 10:17:48 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     Viresh Kumar <viresh.kumar@...aro.org>
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>,
        Sudeep Holla <sudeep.holla@....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 Mon, Oct 19, 2020 at 10:28:27AM +0530, Viresh Kumar wrote:
> On 16-10-20, 12:12, Sudeep Holla wrote:
> > On Fri, Oct 16, 2020 at 07:00:21AM +0100, Sudeep Holla wrote:
> > > On Fri, Oct 16, 2020 at 09:54:34AM +0530, Viresh Kumar wrote:
> > > > On 15-10-20, 19:05, Sudeep Holla wrote:
> > > > > OK, this breaks with SCMI which doesn't provide clocks but manage OPPs
> > > > > directly. Before this change clk_get(dev..) was allowed to fail and
> > > > > --EPROBE_DEFER was not an error.
> > > >
> > > > I think the change in itself is fine. We should be returning from
> > > > there if we get EPROBE_DEFER. The question is rather why are you
> > > > getting EPROBE_DEFER here ?
> > > >
> > >
> > > Ah OK, I didn't spend too much time, saw -EPROBE_DEFER, just reverted
> > > this patch and it worked. I need to check it in detail yet.
> > >
> > 
> > You confused me earlier. As I said there will be no clock provider
> > registered for SCMI CPU/Dev DVFS.
> > 	opp_table->clk = clk_get(dev, NULL);
> > will always return -EPROBE_DEFER as there is no clock provider for dev.
> > But this change now propagates that error to caller of dev_pm_opp_add
> > which means we can't add opp to a device if there are no clock providers.
> > This breaks for DVFS which don't operate separately with clocks and
> > regulators.
>
> The CPUs DT node shouldn't have a clock property in such a case and I
> would expect an error instead of EPROBE_DEFER then. Isn't it ?

Ideally yes, but for legacy reasons clocks property has been used for
providing OPP/DVFS handle too. While we can change and add new property
for that, it will still break old bindings.

--
Regards,
Sudeep