linux-kernel - Re: [PATCH v2 2/5] clk: tegra: Fix refcounting of gate clocks

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Date:   Fri, 15 Jan 2021 16:17:18 +0100
From:   Thierry Reding <thierry.reding@...il.com>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Jonathan Hunter <jonathanh@...dia.com>,
        Peter De Schrijver <pdeschrijver@...dia.com>,
        Prashant Gaikwad <pgaikwad@...dia.com>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>, linux-tegra@...r.kernel.org,
        linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/5] clk: tegra: Fix refcounting of gate clocks

On Tue, Jan 12, 2021 at 03:27:21PM +0300, Dmitry Osipenko wrote:
> The refcounting of the gate clocks has a bug causing the enable_refcnt
> to underflow when unused clocks are disabled. This happens because clk
> provider erroneously bumps the refcount if clock is enabled at a boot
> time, which it shouldn't be doing, and it does this only for the gate
> clocks, while peripheral clocks are using the same gate ops and the
> peripheral clocks are missing the initial bump. Hence the refcount of
> the peripheral clocks is 0 when unused clocks are disabled and then the
> counter is decremented further by the gate ops, causing the integer
> underflow.
> 
> Fix this problem by removing the erroneous bump and by implementing the
> disable_unused() callback, which disables the unused gates properly.
> 
> The visible effect of the bug is such that the unused clocks are never
> gated if a loaded kernel module grabs the unused clocks and starts to use
> them. In practice this shouldn't cause any real problems for the drivers
> and boards supported by the kernel today.
> 
> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
> ---
>  drivers/clk/tegra/clk-periph-gate.c | 72 +++++++++++++++++++----------
>  drivers/clk/tegra/clk-periph.c      | 11 +++++
>  2 files changed, 58 insertions(+), 25 deletions(-)

Acked-by: Thierry Reding <treding@...dia.com>

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