linux-kernel - Re: [PATCH v4 6/6] hwmon: use smp_call_on

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Date:	Mon, 9 May 2016 16:37:01 +0200
From:	Juergen Gross <jgross@...e.com>
To:	Pali Rohár <pali.rohar@...il.com>
Cc:	Guenter Roeck <linux@...ck-us.net>, linux-kernel@...r.kernel.org,
	xen-devel@...ts.xenproject.org, boris.ostrovsky@...cle.com,
	david.vrabel@...rix.com, mingo@...hat.com, peterz@...radead.org,
	Douglas_Warzecha@...l.com, jdelvare@...e.com, tglx@...utronix.de,
	hpa@...or.com, jeremy@...p.org, chrisw@...s-sol.org,
	akataria@...are.com, rusty@...tcorp.com.au,
	virtualization@...ts.linux-foundation.org, x86@...nel.org
Subject: Re: [PATCH v4 6/6] hwmon: use smp_call_on_cpu() for dell-smm i8k

On 21/04/16 15:27, Pali Rohár wrote:
> On Thursday 21 April 2016 15:12:52 Juergen Gross wrote:
>> On 21/04/16 12:57, Pali Rohár wrote:
>>> On Tuesday 05 April 2016 21:31:52 Pali Rohár wrote:
>>>> On Tuesday 05 April 2016 16:54:14 Guenter Roeck wrote:
>>>>> On Tue, Apr 05, 2016 at 07:10:07AM +0200, Juergen Gross wrote:
>>>>>> Use the smp_call_on_cpu() function to call system management
>>>>>> mode on cpu 0.
>>>>>> Make call secure by adding get_online_cpus() to avoid e.g. suspend
>>>>>> resume cycles in between.
>>>>>>
>>>>>> Signed-off-by: Juergen Gross <jgross@...e.com>
>>>>>> ---
>>>>>> V4: add call to get_online_cpus()
>>>>>
>>>>> Pali, any chance to test this ?
>>>>
>>>> I can test it, but just on machine where (probably) smm calls can be 
>>>> send from any cpu... Need some time for testing and I believe I can do 
>>>> that at the end of the week.
>>>
>>> Sorry I had absolutely no more free time last weekend :-( And same
>>> prediction is for this weekend and also next one...
>>
>> Pali, I've got a Dell laptop (Latitude E6440) here. Would this device be
>> okay for a test?
> 
> Hi!
> 
> Proper regression test should check if this patch does not break any
> function or drivers dependent on dcdbas.ko. And should be done on both
> notebook devices: which needs to issue that smm call on cpu 0 and also
> on which it is not needed.

Hmm, couldn't get one which needs smm to be called on cpu 0.
OTOH I've done various tests and added a printk() in raise_smm()
and i8k_smm_func() issuing the cpu number it was called on.

> Some notebooks which needs smm call to issued from cpu 0 can be found in
> git commit messages of i8k, dell-laptop or dcdbas kernel drivers.
> 
>> What would you do for testing? In case you can give me
>> some hints how to do a sensible test I'd do it.
> 
> Test e.g. dell-laptop.ko driver. It provides /sys interface for changing
> keyboard backlight or changing rfkill switches (bluetooth wifi).

Done.

> Also test tools from libsmbios (userspace) package.

Done.

> There must be no difference in output/functionality with or without your
> patches.

Verified.

>> I've verified by adding a printk() to smp_call_on_cpu() that at least
>> one of the modified drivers has been used during system boot.
> 
> Also you can patch i8k/dcdbas smm function to print cpu number on which
> is code running (to verify that it was really called on cpu 0 as
> needed).

Done.

I tested suspend/resume, too, as adding get_online_cpus() might have
changed behavior. Worked like a charm. :-)


Juergen