Re: [PATCH 08/13] clk: qcom: hfpll: CLK_IGNORE_UNUSED

From: Stephen Boyd <sboyd@kernel.org>
To: Jorge Ramirez <jorge.ramirez-ortiz@linaro.org>,
	Viresh Kumar <viresh.kumar@linaro.org>
Cc: Bjorn Andersson <bjorn.andersson@linaro.org>,
	robh+dt@kernel.org, mark.rutland@arm.com, andy.gross@linaro.org,
	david.brown@linaro.org, will.deacon@arm.com,
	mturquette@baylibre.com, jassisinghbrar@gmail.com,
	vkoul@kernel.org, niklas.cassel@linaro.org, sibis@codeaurora.org,
	georgi.djakov@linaro.org, arnd@arndb.de,
	horms+renesas@verge.net.au, heiko@sntech.de,
	enric.balletbo@collabora.com, jagan@amarulasolutions.com,
	olof@lixom.net, amit.kucheria@linaro.org,
	devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org, linux-clk@vger.kernel.org
Subject: Re: [PATCH 08/13] clk: qcom: hfpll: CLK_IGNORE_UNUSED
Date: Tue, 22 Jan 2019 10:47:19 -0800	[thread overview]
Message-ID: <154818283956.20280.2895221927807522124@swboyd.mtv.corp.google.com> (raw)
In-Reply-To: <e55df608-7058-63b9-b449-982d32e08759@linaro.org>

Quoting Jorge Ramirez (2019-01-17 02:46:21)
> On 1/17/19 11:08, Viresh Kumar wrote:
> > On 17-01-19, 09:38, Jorge Ramirez wrote:
> >> COMMON_CLK_DISABLED_UNUSED relies on the enable_count reference counter
> >> to disable the clocks that were enabled by the firwmare and not by the
> >> drivers.
> >>
> >> the cpufreq driver does not enable the cpu clock.
> >>
> >> so when clk_change_rate is called, the enable_count counter is not
> >> incremented and therefore it just remains null since this was enabled by
> >> the firmware.
> >>
> >> I tried doing:
> >>
> >> diff --git a/drivers/cpufreq/cpufreq-dt.c b/drivers/cpufreq/cpufreq-dt.c
> >> index e58bfcb..5a9f83e 100644
> >> --- a/drivers/cpufreq/cpufreq-dt.c
> >> +++ b/drivers/cpufreq/cpufreq-dt.c
> >> @@ -124,6 +124,10 @@ static int resources_available(void)
> >>                 return ret;
> >>         }
> >>
> >> + ret = clk_prepare_enable(cpu_clk);
> >> + if (ret)
> >> +         return ret;
> >> +
> >>         clk_put(cpu_clk);
> >>
> >>         name = find_supply_name(cpu_dev);
> >>
> >>
> >> and that removed the need for CLK_IGNORE_UNUSED. But I am not sure of
> >> the system wide consequences of that change to cpufreq.
> > 
> > If the cpufreq driver enables it then it should disable it on exit as
> > well, right ? And in that case if you unload your driver's module, you
> > will hang the system as the clock will get disabled :)
> 
> ah, of course, sorry was over-thinking this thing :)
> 
> > 
> > Every other platform must either be marking it with CLK_IGNORE_UNUSED
> > or they must be doing clk_enable from somewhere, maybe the CPU online
> > path, not sure though.
> > 
> 
> since this clock is enabled by the firmware, it seems to me that using
> CLK_IGNORE_UNUSED remains the best option.
> 

What do you do about CPUs being offlined? Presumably when the CPU is
gone the system doesn't need to keep the clk enabled anymore.