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

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Message-ID: <20230704195451.7gklbmyautuajqtq@CAB-WSD-L081021>
Date:   Tue, 4 Jul 2023 22:54:51 +0300
From:   Dmitry Rokosov <ddrokosov@...rdevices.ru>
To:     Jerome Brunet <jbrunet@...libre.com>
CC:     <neil.armstrong@...aro.org>, <mturquette@...libre.com>,
        <sboyd@...nel.org>, <khilman@...libre.com>,
        <martin.blumenstingl@...glemail.com>, <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

Hello Jerome,

Thank you for the review!

On Tue, Jul 04, 2023 at 09:43:41PM +0200, Jerome Brunet wrote:
> 
> 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
> 

Do you mean a stack trace or reference to clk_core_enable_lock()?

> >    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 
> 

Ack

> >
> > 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
> 

No problem :) Sometimes 2 lines change is produced during 4 hands
debugging :)

> > ---
> >  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)) {
> 

-- 
Thank you,
Dmitry