linux-kernel - Re: [PATCH v2 1/3] drivers/bus: Add Legacy PM OPS usage check and warning to bus

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Date:	Mon, 06 Jan 2014 14:44:18 -0700
From:	Shuah Khan <shuah.kh@...sung.com>
To:	Greg KH <gregkh@...uxfoundation.org>
Cc:	rjw@...ysocki.net, shuahkhan@...il.com,
	linux-kernel@...r.kernel.org, Shuah Khan <shuah.kh@...sung.com>
Subject: Re: [PATCH v2 1/3] drivers/bus: Add Legacy PM OPS usage check and
 warning to bus_register()

On 01/06/2014 02:29 PM, Greg KH wrote:
> On Mon, Jan 06, 2014 at 01:30:31PM -0700, Shuah Khan wrote:
>> On 01/06/2014 01:17 PM, Greg KH wrote:
>>> On Mon, Jan 06, 2014 at 01:03:21PM -0700, Shuah Khan wrote:
>>>> Add Legacy PM OPS usage checks to bus_register() function. If Legacy PM OPS
>>>> usage is found, print warning message to indicate that the driver code needs
>>>> updating to use Dev PM OPS interfaces. This will help serve as a way to track
>>>> drivers that still use Legacy PM OPS and fix them.
>>>>
>>>> The Legacy PM OPS check looks for suspend(struct device *, pm_message_t) or
>>>> resume(struct device *) bus level interfaces.
>>>>
>>>> Signed-off-by: Shuah Khan <shuah.kh@...sung.com>
>>>> ---
>>>>   drivers/base/bus.c | 3 +++
>>>>   1 file changed, 3 insertions(+)
>>>>
>>>> diff --git a/drivers/base/bus.c b/drivers/base/bus.c
>>>> index 73f6c29..e8753a7 100644
>>>> --- a/drivers/base/bus.c
>>>> +++ b/drivers/base/bus.c
>>>> @@ -916,6 +916,9 @@ int bus_register(struct bus_type *bus)
>>>>   		goto bus_groups_fail;
>>>>
>>>>   	pr_debug("bus: '%s': registered\n", bus->name);
>>>> +	if (bus->suspend || bus->resume)
>>>> +		pr_warn("bus '%s' needs updating - use pm pointer.\n",
>>>> +			bus->name);
>>>
>>> Why can't we just sweep the tree for all of these now, fix them up, and
>>> then delete these fields and be done with it?
>>>
>>> Same for the other ones, putting warnings in the kernel log files
>>> doesn't work at all for getting people to fix up their code (see
>>> examples of scsi log messages being there for _years_ about obsolete
>>> driver interfaces being used.)
>>
>> This change is not a simple case of replacing legacy with pm ops. I have
>> been working on changing drivers that use legacy, in some cases it is an
>> easy change, however in some cases it requires adding new interfaces to port
>> over from legacy to pm ops. Legacy suspend/resume is more course grain and
>> pm ops offer fine grain control over suspend, hibernate etc. Also it has
>> been a challenge without the hardware to test.
>>
>> My thinking is adding warning might get the attention of individual driver
>> owners.
>
> If it's not a trivial change, and takes a lot of work by someone who
> knows this type of thing (i.e. you), then I wouldn't start making kernel
> log warnings about this, it's just going to annoy a bunch of people :)

ok I will continue fixing the drivers. :)

>
> Again, see the SCSI log warnings for examples of this, people just tune
> them out, assuming someone else is going to fix the issue, someday.  And
> that someday never comes...
>

Yeah. Warnings could just get ignored.

-- Shuah

-- 
Shuah Khan
Senior Linux Kernel Developer - Open Source Group
Samsung Research America(Silicon Valley)
shuah.kh@...sung.com | (970) 672-0658
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