From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bjorn Andersson Subject: Re: [PATCH v3 08/14] clk: qcom: hfpll: CLK_IGNORE_UNUSED Date: Thu, 11 Jul 2019 08:16:31 -0700 Message-ID: <20190711151631.GI7234@tuxbook-pro> References: <20190625164733.11091-1-jorge.ramirez-ortiz@linaro.org> <20190625164733.11091-9-jorge.ramirez-ortiz@linaro.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20190625164733.11091-9-jorge.ramirez-ortiz@linaro.org> Sender: linux-kernel-owner@vger.kernel.org To: Jorge Ramirez-Ortiz Cc: sboyd@kernel.org, david.brown@linaro.org, jassisinghbrar@gmail.com, mark.rutland@arm.com, mturquette@baylibre.com, robh+dt@kernel.org, will.deacon@arm.com, arnd@arndb.de, horms+renesas@verge.net.au, heiko@sntech.de, sibis@codeaurora.org, enric.balletbo@collabora.com, jagan@amarulasolutions.com, olof@lixom.net, vkoul@kernel.org, niklas.cassel@linaro.org, georgi.djakov@linaro.org, amit.kucheria@linaro.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-clk@vger.kernel.org, linux-arm-msm@vger.kernel.org, khasim.mohammed@linaro.org List-Id: devicetree@vger.kernel.org On Tue 25 Jun 09:47 PDT 2019, Jorge Ramirez-Ortiz wrote: > When COMMON_CLK_DISABLED_UNUSED is set, in an effort to save power and > to keep the software model of the clock in line with reality, the > framework transverses the clock tree and disables those clocks that > were enabled by the firmware but have not been enabled by any device > driver. > > If CPUFREQ is enabled, early during the system boot, it might attempt > to change the CPU frequency ("set_rate"). If the HFPLL is selected as > a provider, it will then change the rate for this clock. > > As boot continues, clk_disable_unused_subtree will run. Since it wont > find a valid counter (enable_count) for a clock that is actually > enabled it will attempt to disable it which will cause the CPU to > stop. But if CPUfreq has acquired the CPU clock and the hfpll is the currently selected input, why does the clock framework not know about this clock being used? > Notice that in this driver, calls to check whether the clock is > enabled are routed via the is_enabled callback which queries the > hardware. > > The following commit, rather than marking the clock critical and > forcing the clock to be always enabled, addresses the above scenario > making sure the clock is not disabled but it continues to rely on the > firmware to enable the clock. > > Co-developed-by: Niklas Cassel > Signed-off-by: Niklas Cassel > Signed-off-by: Jorge Ramirez-Ortiz I can see that we have a real issue in the case where CPUfreq is not enabled and hence there are no clients, according to Linux. And that I don't know another way to guard against. Reviewed-by: Bjorn Andersson Regards, Bjorn > --- > drivers/clk/qcom/hfpll.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/drivers/clk/qcom/hfpll.c b/drivers/clk/qcom/hfpll.c > index 0ffed0d41c50..d5fd27938e7b 100644 > --- a/drivers/clk/qcom/hfpll.c > +++ b/drivers/clk/qcom/hfpll.c > @@ -58,6 +58,13 @@ static int qcom_hfpll_probe(struct platform_device *pdev) > .parent_names = (const char *[]){ "xo" }, > .num_parents = 1, > .ops = &clk_ops_hfpll, > + /* > + * rather than marking the clock critical and forcing the clock > + * to be always enabled, we make sure that the clock is not > + * disabled: the firmware remains responsible of enabling this > + * clock (for more info check the commit log) > + */ > + .flags = CLK_IGNORE_UNUSED, > }; > > h = devm_kzalloc(dev, sizeof(*h), GFP_KERNEL); > -- > 2.21.0 >