linux-kernel - Re: [PATCH 1/2] async: async device driver probing

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Message-ID: <20140813221044.GA11620@core.coreip.homeip.net>
Date:	Wed, 13 Aug 2014 15:10:44 -0700
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Greg KH <gregkh@...uxfoundation.org>
Cc:	falcon@...zu.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] async: async device driver probing

On Thu, Aug 14, 2014 at 06:02:23AM +0800, Greg KH wrote:
> On Wed, Aug 13, 2014 at 10:20:33AM -0700, Dmitry Torokhov wrote:
> > Hi Greg,
> > 
> > On Sat, Feb 08, 2014 at 10:27:29AM -0800, Greg KH wrote:
> 
> February?  That's an old thread to dig up...

Well, yes ;)

> 
> 
> > > On Sat, Feb 08, 2014 at 07:05:38PM +0800, falcon@...zu.com wrote:
> > > > From: Wu Zhangjin <wuzhangjin@...il.com>
> > > > 
> > > > [*Note*: NOT applicable, only for comments.]
> > > > 
> > > > To async the slow driver probing function of some devices, the device probing
> > > > support is modified to support async scheduling.
> > > > 
> > > > In order to async your driver probing function, please mask the async_probe
> > > > flag to 1, and to make sure one asynced probing is executed before an specified
> > > > point, please call async_synchronize_full() in that point..
> > > > 
> > > > Usage:
> > > > 
> > > > 	static struct i2c_driver test_driver = {
> > > > 		.driver = {
> > > > 			.name   = TEST_DEV_NAME,
> > > > 			.owner  = THIS_MODULE,
> > > > 	+               .async_probe = 1,
> > > > 		},
> > > 
> > > Why is this needed, we have defered probing and the container stuff, so
> > > what problem is this solving?
> > 
> > Deferred probing only helps if resources are not ready yet, but
> > sometimes we have a slow(ish) device which initialization stalls probing
> > the rest of the system. For example a touchpad can take up to a second
> > to calibrate itself after reset. One could try scheduling reset
> > asynchronously, or try to offload it to open(), but that is not always
> > best:
> > 
> > 1. Manual async: what to do when reset fails? Ideally we do not want to
> > leave driver half-way bound with device not operable, but much rather
> > signal the rest of the system that binding of the device failed and
> > release all resources.
> > 
> > 2. Offload to open: the same issue as with manually doing async reset,
> > plus sometimes we do not know all parameters that we should create input
> > device with until after we reset physical device and queried it for
> > capabilities.
> > 
> > Marking a driver to tell device core to execute probe asynchronously [at
> > boot time] seems like a very appealing feature from driver author POV.
> > 
> > What is the container stuff you mention?
> 
> drivers/base/container.c

I am not sure how that would help in the scenario described above, as it
seems ACPI specific...

Thanks.

-- 
Dmitry
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