linux-kernel - Re: [PATCH v2 08/14] clk: qcom: hfpll: CLK_IGNORE

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Date:   Fri, 22 Feb 2019 10:12:33 -0800
From:   Stephen Boyd <sboyd@...nel.org>
To:     andy.gross@...aro.org, arnd@...db.de, bjorn.andersson@...aro.org,
        david.brown@...aro.org, enric.balletbo@...labora.com,
        heiko@...ech.de, horms+renesas@...ge.net.au,
        jagan@...rulasolutions.com, jassisinghbrar@...il.com,
        jorge.ramirez-ortiz@...aro.org, mark.rutland@....com,
        mturquette@...libre.com, olof@...om.net, robh+dt@...nel.org,
        sibis@...eaurora.org, will.deacon@....com
Cc:     vkoul@...nel.org, niklas.cassel@...aro.org,
        georgi.djakov@...aro.org, amit.kucheria@...aro.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-clk@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, khasim.mohammed@...aro.org
Subject: Re: [PATCH v2 08/14] clk: qcom: hfpll: CLK_IGNORE_UNUSED

Quoting Jorge Ramirez-Ortiz (2019-01-28 10:32:55)
> 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. 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 <niklas.cassel@...aro.org>
> Signed-off-by: Niklas Cassel <niklas.cassel@...aro.org>
> Signed-off-by: Jorge Ramirez-Ortiz <jorge.ramirez-ortiz@...aro.org>
> ---
>  drivers/clk/qcom/hfpll.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/clk/qcom/hfpll.c b/drivers/clk/qcom/hfpll.c
> index 0ffed0d..9d92f5d 100644
> --- a/drivers/clk/qcom/hfpll.c
> +++ b/drivers/clk/qcom/hfpll.c
> @@ -58,6 +58,7 @@ static int qcom_hfpll_probe(struct platform_device *pdev)
>                 .parent_names = (const char *[]){ "xo" },
>                 .num_parents = 1,
>                 .ops = &clk_ops_hfpll,
> +               .flags = CLK_IGNORE_UNUSED,

Please put some sort of similar comment in the code so we can find it
without git history digging.