Re: [PATCH] clk: Don't try to enable critical clocks if prepare failed

[Guenter Roeck]

On 12/26/19 1:51 AM, Jerome Brunet wrote:
> On Wed 25 Dec 2019 at 17:34, Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
>
> > The following traceback is seen if a critical clock fails to prepare.
> >
> > bcm2835-clk 3f101000.cprman: plld: couldn't lock PLL
> > ------------[ cut here ]------------
> > Enabling unprepared plld_per
> > WARNING: CPU: 1 PID: 1 at drivers/clk/clk.c:1014 clk_core_enable+0xcc/0x2c0
> > ...
> > Call trace:
> >   clk_core_enable+0xcc/0x2c0
> >   __clk_register+0x5c4/0x788
> >   devm_clk_hw_register+0x4c/0xb0
> >   bcm2835_register_pll_divider+0xc0/0x150
> >   bcm2835_clk_probe+0x134/0x1e8
> >   platform_drv_probe+0x50/0xa0
> >   really_probe+0xd4/0x308
> >   driver_probe_device+0x54/0xe8
> >   device_driver_attach+0x6c/0x78
> >   __driver_attach+0x54/0xd8
> > ...
> >
> > Check return values from clk_core_prepare() and clk_core_enable() and
> > bail out if any of those functions returns an error.
> >
> > Cc: Jerome Brunet <jbrunet@xxxxxxxxxxxx>
> > Fixes: 99652a469df1 ("clk: migrate the count of orphaned clocks at init")
> > Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx>
> > ---
> >   drivers/clk/clk.c | 10 ++++++++--
> >   1 file changed, 8 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> > index 6a11239ccde3..772258de2d1f 100644
> > --- a/drivers/clk/clk.c
> > +++ b/drivers/clk/clk.c
> > @@ -3426,11 +3426,17 @@ static int __clk_core_init(struct clk_core *core)
> >   	if (core->flags & CLK_IS_CRITICAL) {
> >   		unsigned long flags;
> >   
> > -		clk_core_prepare(core);
> > +		ret = clk_core_prepare(core);
> > +		if (ret)
> > +			goto out;
> >   
> >   		flags = clk_enable_lock();
> > -		clk_core_enable(core);
> > +		ret = clk_core_enable(core);
> >   		clk_enable_unlock(flags);
> > +		if (ret) {
> > +			clk_core_unprepare(core);
> > +			goto out;
> > +		}
>
> Hi Guenter,
>
> It looks like it was a mistake to discard the possibility of a failure
> here. Thanks for correcting this.
>
> However, we would not want a critical clock to silently fail to
> enable. This might lead to unexpected behavior which are generally hard
> (and annoying) to debug.
>
> Would you mind adding some kind of warning trace in case this fails ?

The really relevant information is:

bcm2835-clk 3f101000.cprman: plld: couldn't lock PLL

which is already displayed (and not surprising since cprman isn't implemented
in qemu). While I agree that an error message might be useful, replacing
one traceback with another doesn't really make sense to me, and I am not
really a friend of spreading tracebacks throughout the kernel. Please feel
free to consider this patch to be a bug report, and feel free to ignore it
and suggest something else.

Thanks,
Guenter