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

[Jerome Brunet <jbrunet@baylibre.com>]

On Tue 04 Jul 2023 at 22:54, Dmitry Rokosov <ddrokosov@sberdevices.ru> wrote:

> 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@sberdevices.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()?

The comment about clk_core_enable_lock.
The stack trace is useful, it may help people googling the warning

>
>> >    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@sberdevices.ru>
>> > Signed-off-by: Dmitry Rokosov <ddrokosov@sberdevices.ru>
>> > Signed-off-by: Jan Dakinevich <yvdakinevich@sberdevices.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)) {
>> 


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