Re: [PATCH v5 2/7] clk: tegra: Fix refcounting of gate clocks

Michał Mirosław
2021-03-18T09:14:41Z

On Wed, Mar 17, 2021 at 10:30:01PM +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.
[...]
> diff --git a/drivers/clk/tegra/clk-periph-gate.c b/drivers/clk/tegra/clk-periph-gate.c
> index 4b31beefc9fc..3c4259fec82e 100644
> --- a/drivers/clk/tegra/clk-periph-gate.c
> +++ b/drivers/clk/tegra/clk-periph-gate.c
[...]
> @@ -91,21 +108,28 @@ static void clk_periph_disable(struct clk_hw *hw)
>
> spin_lock_irqsave(&periph_ref_lock, flags);
>
> - gate->enable_refcnt[gate->clk_num]--;
> - if (gate->enable_refcnt[gate->clk_num] > 0) {
> - spin_unlock_irqrestore(&periph_ref_lock, flags);
> - return;
> - }
> + WARN_ON(!gate->enable_refcnt[gate->clk_num]);
> +
> + if (gate->enable_refcnt[gate->clk_num]-- == 1)
> + clk_periph_disable_locked(hw);

Nit: "if (--n == 0)" seems more natural, as you want to call
clk_periph_disable_locked() when the refcount goes down to 0.

[...]
> /*
> - * If peripheral is in the APB bus then read the APB bus to
> - * flush the write operation in apb bus. This will avoid the
> - * peripheral access after disabling clock
> + * Some clocks are duplicated and some of them are marked as critical,
> + * like fuse and fuse_burn for example, thus the enable_refcnt will
> + * be non-zero here id the "unused" duplicate is disabled by CCF.

s/id/if/ ?

Best Regards
Michał Mirosław