linux-kernel - Re: [PATCH v1] clk: meson: change usleep_range() to udelay() for atomic context

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Message-ID: <1j352378zh.fsf@starbuckisacylon.baylibre.com>
Date:   Tue, 04 Jul 2023 21:43:41 +0200
From:   Jerome Brunet <jbrunet@...libre.com>
To:     Dmitry Rokosov <ddrokosov@...rdevices.ru>,
        neil.armstrong@...aro.org, mturquette@...libre.com,
        sboyd@...nel.org, khilman@...libre.com,
        martin.blumenstingl@...glemail.com
Cc:     jian.hu@...ogic.com, kernel@...rdevices.ru, rockosov@...il.com,
        linux-amlogic@...ts.infradead.org, linux-clk@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Jan Dakinevich <yvdakinevich@...rdevices.ru>
Subject: Re: [PATCH v1] clk: meson: change usleep_range() to udelay() for
 atomic context


On Mon 03 Jul 2023 at 23:04, Dmitry Rokosov <ddrokosov@...rdevices.ru> wrote:

> The function meson_clk_pll_enable() can be invoked under the enable_lock
> spinlock from the clk core logic

---
> (please refer to
> drivers/clk/clk.c:clk_core_enable_lock()), which risks a kernel panic
> during the usleep_range() call:
>

This part of the comment is not very useful - please drop it

>    BUG: scheduling while atomic: kworker/u4:2/36/0x00000002
>    Modules linked in: g_ffs usb_f_fs libcomposite
>    CPU: 1 PID: 36 Comm: kworker/u4:2 Not tainted 6.4.0-rc5 #273
>    Workqueue: events_unbound async_run_entry_fn
>    Call trace:
>     dump_backtrace+0x9c/0x128
>     show_stack+0x20/0x38
>     dump_stack_lvl+0x48/0x60
>     dump_stack+0x18/0x28
>     __schedule_bug+0x58/0x78
>     __schedule+0x828/0xa88
>     schedule+0x64/0xd8
>     schedule_hrtimeout_range_clock+0xd0/0x208
>     schedule_hrtimeout_range+0x1c/0x30
>     usleep_range_state+0x6c/0xa8
>     meson_clk_pll_enable+0x1f4/0x310
>     clk_core_enable+0x78/0x200
>     clk_core_enable+0x58/0x200
>     clk_core_enable+0x58/0x200
>     clk_core_enable+0x58/0x200
>     clk_enable+0x34/0x60
>
> Considering that this code is expected to be used in an atomic context,
> it is required to use the udelay() function instead of usleep_range()
> for the atomic context safety.

Please use an imperative form, instructing the code to change 

>
> Fixes: b6ec400aa153 ("clk: meson: introduce new pll power-on sequence for A1 SoC family")
> Reported-by: Jan Dakinevich <yvdakinevich@...rdevices.ru>
> Signed-off-by: Dmitry Rokosov <ddrokosov@...rdevices.ru>
> Signed-off-by: Jan Dakinevich <yvdakinevich@...rdevices.ru>

The tags are confusing here
I suppose a 2 lines change has not be been written with 4 hands ;)

If Jan just reported and you made the change then drop his signed-off
If he did the job, then drop the reported-by and change the author

> ---
>  drivers/clk/meson/clk-pll.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/clk/meson/clk-pll.c b/drivers/clk/meson/clk-pll.c
> index 56ec2210f1ad..eef6f37c8d8d 100644
> --- a/drivers/clk/meson/clk-pll.c
> +++ b/drivers/clk/meson/clk-pll.c
> @@ -367,9 +367,9 @@ static int meson_clk_pll_enable(struct clk_hw *hw)
>  	 * 3. enable the lock detect module
>  	 */
>  	if (MESON_PARM_APPLICABLE(&pll->current_en)) {
> -		usleep_range(10, 20);
> +		udelay(10);
>  		meson_parm_write(clk->map, &pll->current_en, 1);
> -		usleep_range(40, 50);
> +		udelay(40);
>  	};
>  
>  	if (MESON_PARM_APPLICABLE(&pll->l_detect)) {