linux-kernel - Re: [PATCH v2] clk: tegra: Use readl_relaxed_poll_timeout_atomic in tegra210_clock

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Message-ID: <20171019184223.GA7415@Asurada-Nvidia>
Date:   Thu, 19 Oct 2017 11:42:24 -0700
From:   Nicolin Chen <nicoleotsuka@...il.com>
To:     Thierry Reding <thierry.reding@...il.com>
Cc:     sboyd@...eaurora.org, pdeschrijver@...dia.com,
        linux-kernel@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-clk@...r.kernel.org, jonathanh@...dia.com,
        mturquette@...libre.com, pgaikwad@...dia.com
Subject: Re: [PATCH v2] clk: tegra: Use readl_relaxed_poll_timeout_atomic in
 tegra210_clock_init

On Thu, Oct 19, 2017 at 11:44:22AM +0200, Thierry Reding wrote:
> > > Below is the call trace of tegra210_init_pllu() function:
> > >   start_kernel()
> > >   -> time_init()
> > >   --> of_clk_init()
> > >   ---> tegra210_clock_init()
> > >   ----> tegra210_pll_init()
> > >   -----> tegra210_init_pllu()

> I'm wondering why we're not seeing a splat for this. Usually the kernel
> will warn if you sleep during atomic context. Does this mean we're just
> not hitting that case?

Yes.

> readx_poll_timeout() has a might_sleep_if(), and
> therefore it should always cause the splat.

That's true as long as CONFIG_DEBUG_ATOMIC_SLEEP is enabled locally.

> Any ideas why this has gone unnoticed for all this time?

We can see in the tegra210_init_pllu() function that it'll not call
tegra210_enable_pllu() if pllu is already enabled (by bootloader).

You can verify it by adding an irqs_disabled() in this routine. The
function is called during system-boot and suspend-n-resume. And both
cases should be irqs_disabled().

Thanks
Nicolin