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

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Message-ID: <20140814041834.GA7727@kroah.com>
Date:	Thu, 14 Aug 2014 12:18:34 +0800
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	falcon@...zu.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] async: async device driver probing

On Wed, Aug 13, 2014 at 03:10:44PM -0700, Dmitry Torokhov wrote:
> 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...

It is?  I thought the drm people were using it on ARM.  I really don't
know, sorry, don't have the chance to check it right now...

greg k-h
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