Re: [PATCH] clk: scpi: error when clock fails to register

[Sudeep Holla <sudeep.holla@arm.com>]

Hi Jerome,

On 29/06/17 09:50, Jerome Brunet wrote:
> On Wed, 2017-06-28 at 18:07 +0100, Sudeep Holla wrote:
>>
>> On 28/06/17 17:46, Jerome Brunet wrote:
>>> On Wed, 2017-06-28 at 16:52 +0100, Sudeep Holla wrote:
>>
>> [..]
>>
>>>>
>>>> Thanks for this stack. I just worked out the same path now. I did come
>>>> up with the patch as below. That should work if my understanding is
>>>> correct.
>>>
>>> I tried.
>>
>> Thanks.
>>
>>> It does not work unfortunately. Still crashes but somewhere else:
>>> [    2.301482] [<ffff00000849e67c>] scpi_of_clk_src_get+0x14/0x58
>>> [    2.307261] [<ffff000008495f40>] __of_clk_get_by_name+0x100/0x118
>>> [    2.313297] [<ffff000008495fac>] clk_get+0x2c/0x78
>>> [    2.318044] [<ffff00000856f4d0>] dev_pm_opp_get_opp_table+0xb0/0x118
>>> [    2.324338] [<ffff00000856fd00>] dev_pm_opp_add+0x20/0x68
>>> [    2.329687] [<ffff0000087a04f8>] scpi_init_opp_table+0xa8/0x188
>>> [    2.335550] [<ffff00000879fb20>]
>>> _get_cluster_clk_and_freq_table+0x80/0x180
>>> [    2.342450] [<ffff0000087a0010>] bL_cpufreq_init+0x3f0/0x480
>>> [    2.348056] [<ffff00000879e4a0>] cpufreq_online+0xc0/0x658
>>> [    2.353490] [<ffff00000879eac8>] cpufreq_add_dev+0x78/0x88
>>> [    2.358924] [<ffff00000855b684>] subsys_interface_register+0x84/0xc8
>>> [    2.365220] [<ffff00000879d8f8>] cpufreq_register_driver+0x138/0x1b8
>>> [    2.371516] [<ffff0000087a0114>] bL_cpufreq_register+0x74/0x120
>>> [    2.377381] [<ffff0000087a0600>] scpi_cpufreq_probe+0x28/0x38
>>> [    2.383076] [<ffff00000855efb0>] platform_drv_probe+0x50/0xb8
>>> [    2.388766] [<ffff00000855d144>] driver_probe_device+0x21c/0x2d8
>>>
>>
>> Looks like a different route and I know why. I have added an extra check
>> now which should work if I have not missed anything more.
>>
>>> I have not looked at ALL the clock providers, but I have seen a few and I
>>> don't
>>> remember seeing any which fails, at some point, to register a clocks and
>>> still
>>> register successfully. 
>>>
>>
>> No problem, as I said I am fine with the patch you sent as a fix for now
>> but just curious to know what are the issues to be fixed to continue
>> supporting that feature. Please bear with me.
> 
> I am :) and I understand what you are trying to do, having a degraded clock
> provider is better than nothing according to you, correct?
> 
> I'm wondering whether this is correct or not, that why I'm challenging this a
> bit.
> 

Fair enough. But the situation I had on my platform is that it provides
DVFS support for 2 CPU clusters and 1 GPU domain. I didn't want to block
using CPUFreq until GPU DVFS was properly supported in the firmware.
I had similar situation with the clock and hence I allowed it to continue.

> If you failed to register an scpi clock it is probably because the communication
> with the FW is not working, or at least 'not that good', right ?
> 

Not exactly, what if the error is for that particular clock. That's my
point. If we have reached so far means the communication is fine. Just a
fault piece of hardware which may not be critical.

> If for some reason, you manage to register some other clocks from the same FW,
> how confident can you be that communication will be ok for them ? that the
> settings you request will be applied correctly ?
> 

Not sure, I am not registering the clock. Think SCPI as a single clock
provider with multiple clock outputs. You don't want to disable it
entirely if one of the clock outputs have problem. That's my counter
argument.

> Is it possible that you may be causing more harm/damage playing with a broken HW
> ?
> 
Not sure how if we are not registering that clock output from the h/w
clock provider perspective.

>>
>>> It seems strange to continue with a broken controller.
>>>
>>
>> I would have agreed if it was single driver or h/w controlled by Linux.
>> Since it's in the firmware, we should allow the working clocks/opps to
>> work though few are broken. It's not good if we had to disable
>> everything if some piece of firmware is not yet ready or broken.
>> But again, we can get it working later, for now, I am fine with you patch.
> 
> I tried your last version, and it does not Oops, at least not for me.
> 
> The end result still looks odd to me:
> [    1.115219] scpi_clocks scpi:clocks: failed to register clock 'vcpu'
> [    1.159490] cpu cpu0: _get_cluster_clk_and_freq_table: Failed to get clk for
> cpu: 0, cluster: 0
> [    1.162986] cpu cpu0: _get_cluster_clk_and_freq_table: Failed to get data for
> cluster: 0
> [    1.170945] cpu cpu1: _get_cluster_clk_and_freq_table: Failed to get clk for
> cpu: 1, cluster: 0
> [    1.179634] cpu cpu1: _get_cluster_clk_and_freq_table: Failed to get data for
> cluster: 0
> [    1.187654] cpu cpu2: _get_cluster_clk_and_freq_table: Failed to get clk for
> cpu: 2, cluster: 0
> [    1.196284] cpu cpu2: _get_cluster_clk_and_freq_table: Failed to get data for
> cluster: 0
> [    1.204375] cpu cpu3: _get_cluster_clk_and_freq_table: Failed to get clk for
> cpu: 3, cluster: 0
> [    1.212911] cpu cpu3: _get_cluster_clk_and_freq_table: Failed to get data for
> cluster: 0
> [    1.220612] arm_big_little: bL_cpufreq_register: Registered platform driver:
> scpi
> 
> So now, I have an scpi clock provider which registers successfully but fails to
> register its only clock. As a consequence, I also have a cpufreq driver which
> manages to register but has no clock cpu clock to drive ...
> 

Yes, I agree the above is not entirely acceptable situation.

-- 
Regards,
Sudeep