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

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Date:   Thu, 26 Dec 2019 09:22:10 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Jerome Brunet <jbrunet@...libre.com>,
        Michael Turquette <mturquette@...libre.com>
Cc:     Stephen Boyd <sboyd@...nel.org>, linux-clk@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] clk: Don't try to enable critical clocks if prepare
 failed

On 12/26/19 1:51 AM, Jerome Brunet wrote:
> 
> On Wed 25 Dec 2019 at 17:34, Guenter Roeck <linux@...ck-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@...libre.com>
>> Fixes: 99652a469df1 ("clk: migrate the count of orphaned clocks at init")
>> Signed-off-by: Guenter Roeck <linux@...ck-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