linux-kernel - Re: [PATCH v3 1/2] soc/tegra: pmc: Query PCLK clock rate at probe time

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Message-ID: <20190802133846.GC3883@pdeschrijver-desktop.Nvidia.com>
Date:   Fri, 2 Aug 2019 16:38:46 +0300
From:   Peter De Schrijver <pdeschrijver@...dia.com>
To:     Dmitry Osipenko <digetx@...il.com>
CC:     Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        <linux-tegra@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/2] soc/tegra: pmc: Query PCLK clock rate at probe
 time

On Tue, Jul 30, 2019 at 08:40:19PM +0300, Dmitry Osipenko wrote:
> The PCLK clock is running off SCLK, which is a critical clock that is
> very unlikely to randomly change its rate. It is possible to get a
> lockup if kernel decides to enter LP2 cpuidle from a clk-notifier, which
> happens occasionally in a case of Tegra30 EMC driver that waits for the
> clk-change event in the clk-notify handler, because CCF's 'prepare' mutex
> in kept locked and thus clk_get_rate() wants to sleep with interrupts
> being disabled.
> 

I don't think this is the right solution. Eventually we will want to
scale sclk and pclk because the clock tree power of those is not
insignificant. Maybe register a notifier which updates the PMC timer
values when pclk changes?

Peter.