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From: Peter Mamonov <pmamonov@gmail.com>
To: Alexander Aring <alex.aring@gmail.com>
Cc: barebox <barebox@lists.infradead.org>
Subject: Re: [RFC] device probe order
Date: Thu, 24 Dec 2015 16:42:25 +0300	[thread overview]
Message-ID: <20151224164225.25665d7f@berta> (raw)
In-Reply-To: <20151224124837.0fcc6fce@berta>

On Thu, 24 Dec 2015 12:48:37 +0300
Peter Mamonov <pmamonov@gmail.com> wrote:

> On Wed, 23 Dec 2015 18:04:43 +0100
> Alexander Aring <alex.aring@gmail.com> wrote:
> 
> > On Wed, Dec 23, 2015 at 07:56:44PM +0300, Peter Mamonov wrote:
> > > On Wed, 23 Dec 2015 17:35:51 +0100
> > > Alexander Aring <alex.aring@gmail.com> wrote:
> > > 
> > > > On Wed, Dec 23, 2015 at 07:10:58PM +0300, Peter Mamonov wrote:
> > > > > Dear All,
> > > > > 
> > > > > I've ported an UHCI driver from the u-boot to the barebox
> > > > > (WIP). To interoperate with the EHCI driver, the UHCI driver
> > > > > should be probed ater the EHCI driver. Both drivers are binded
> > > > > via the device tree mechanism. How can i achieve the correct
> > > > > probe order?
> > > > > 
> > > > 
> > > > Normally this should done by returning "-EPROBE_DEFER" inside
> > > > the probe function. There was some RFC last years for supporting
> > > > EPROBE_DEFER [0] and it seems these are mainline.
> > > > 
> > > > However you need some bool which indicates that the EHCI driver
> > > > is probed.
> > > 
> > > Thanks, Alex. As i understand, this is the linux-way solution.
> > > 
> > > Sasha, is it ok to add a global variable to indicate the EHCI
> > > presence? Or should we follow the way proposed by the mentioned
> > > RFCs, i.e. introduce dependencies between drivers?
> > > 
> > 
> > mhhh, maybe a simple "get_device_by_name" works here.
> > 
> > If returning NULL then return -EPROBE_DEFER. Don't know if this is a
> > good solution, name need to be unique then.
> > 
> > 
> > btw:
> > Just found that "of_find_device_by_node" returns -EPROBE_DEFER when
> > nothing was found. This was introduced by the patch series.
> 
> I like this approach better, than introducing a global variable.
> Will look further into it.

Unfortunately of_find_device_by_node() returns a valid pointer to
the device before the device probe function is called. I guess
get_device_by_name() behaves in the same way.

> 
> > 
> > Maybe it helps to look how the current use-cases deals with
> > -EPROBE_DEFER or get_device_by_name is enough.
> > 
> > - Alex
> > 
> 


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  reply	other threads:[~2015-12-24 13:39 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-12-23 16:10 Peter Mamonov
2015-12-23 16:35 ` Alexander Aring
2015-12-23 16:56   ` Peter Mamonov
2015-12-23 17:04     ` Alexander Aring
2015-12-24  9:48       ` Peter Mamonov
2015-12-24 13:42         ` Peter Mamonov [this message]
2016-01-04  8:56           ` Sascha Hauer
2015-12-23 19:46 ` Sascha Hauer
2015-12-24 10:46   ` Peter Mamonov
2015-12-24 14:35     ` Alexander Aring
2015-12-24 16:10       ` Peter Mamonov
2015-12-25 10:21         ` Alexander Aring

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