linux-kernel - Re: Alternative approach to solve the deferred probe

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Date:	Wed, 21 Oct 2015 08:36:23 -0700
From:	Frank Rowand <frowand.list@...il.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
CC:	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Tomeu Vizoso <tomeu.vizoso@...labora.com>,
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Subject: Re: Alternative approach to solve the deferred probe

On 10/21/2015 1:18 AM, Russell King - ARM Linux wrote:
> On Tue, Oct 20, 2015 at 08:58:19PM -0700, Frank Rowand wrote:
>> On 10/20/2015 8:46 AM, Russell King - ARM Linux wrote:

< snip >

>>> +
>>>  static bool driver_deferred_probe_enable = false;
>>> +
>>>  /**
>>>   * driver_deferred_probe_trigger() - Kick off re-probing deferred devices
>>>   *
>>> @@ -188,6 +210,13 @@ static int deferred_probe_initcall(void)
>>>  	driver_deferred_probe_trigger();
>>
>> Couldn't you put the "driver_deferred_probe_report = true" here?  And then
>> not add another round of probes.
> 
> The idea is not to report anything for drivers that were deferred
> during the normal bootup.  The above is part of the normal bootup,
> and the deferred activity should not be warned about.

The above is currently the last point for probe to succeed or defer
(until possibly, as you mentioned, module loading resolves the defer).
If a probe defers above, it will defer again below.  The set of defers
should be exactly the same above and below.

> 
> If we have any devices still deferring after _this_ round, that must
> indicate that some resource they want is not available, and that
> should be warned about.
> 
> Of course, modules can defer too - and I made some suggestions in my
> waffle above the patch about that.
> 

< adding back trimmed, for fuller context >

>>>  	/* Sort as many dependencies as possible before exiting initcalls */
>>>  	flush_workqueue(deferred_wq);
>>> +
>>> +	/* Now one final round, reporting any devices that remain deferred */
>>> +	driver_deferred_probe_report = true;
>>> +	driver_deferred_probe_trigger();
>>> +	/* Sort as many dependencies as possible before exiting initcalls */
>>> +	flush_workqueue(deferred_wq);
>>> +
>>>  	return 0;
>>>  }
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