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SubjectRe: [PATCH] clk: Don't try to enable critical clocks if prepare failed
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On 12/26/19 1:51 AM, Jerome Brunet wrote:
>
> On Wed 25 Dec 2019 at 17:34, Guenter Roeck <linux@roeck-us.net> 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@baylibre.com>
>> Fixes: 99652a469df1 ("clk: migrate the count of orphaned clocks at init")
>> Signed-off-by: Guenter Roeck <linux@roeck-us.net>
>> ---
>> 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

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