netdev - Re: [PATCH v2 2/4] driver core: enable drivers to use deferred probe from init

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Date:	Mon, 28 Jul 2014 16:46:44 -0700
From:	Greg KH <gregkh@...uxfoundation.org>
To:	"Luis R. Rodriguez" <mcgrof@...not-panic.com>
Cc:	Santosh Rastapur <santosh@...lsio.com>,
	Hariprasad S <hariprasad@...lsio.com>,
	Takashi Iwai <tiwai@...e.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
	Joseph Salisbury <joseph.salisbury@...onical.com>,
	Kay Sievers <kay@...y.org>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	Tim Gardner <tim.gardner@...onical.com>,
	Pierre Fersing <pierre-fersing@...rref.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Benjamin Poirier <bpoirier@...e.de>,
	Nagalakshmi Nandigama <nagalakshmi.nandigama@...gotech.com>,
	Praveen Krishnamoorthy <praveen.krishnamoorthy@...gotech.com>,
	Sreekanth Reddy <sreekanth.reddy@...gotech.com>,
	Abhijit Mahajan <abhijit.mahajan@...gotech.com>,
	MPT-FusionLinux.pdl@...gotech.com,
	Linux SCSI List <linux-scsi@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH v2 2/4] driver core: enable drivers to use deferred probe
 from init

On Mon, Jul 28, 2014 at 12:48:32PM -0700, Luis R. Rodriguez wrote:
> On Mon, Jul 28, 2014 at 12:04 PM, Luis R. Rodriguez
> <mcgrof@...not-panic.com> wrote:
> > On Mon, Jul 28, 2014 at 11:55 AM, Greg KH <gregkh@...uxfoundation.org> wrote:
> >> So, what drivers are having problems in their init sequence, and why
> >> aren't they using async firmware loading?
> >
> > Fixing drivers is one thing, fixing drivers *now* because *now*
> > drivers are failing due to a regression is another thing and that's
> > what we have now so lets just be clear on that. The 30 second rule is
> > a major driver requirement change and it should not be taken slightly,
> > all of a sudden this is a new requirement but you won't know that
> > unless you're reading these threads or hit an issue. That's an issue
> > in itself.

That "regression" is something that userspace has decided to do, not
anything the kernel changed, so perhaps you should just patch your
modprobe and be done with it until you can fix up those drivers?

And putting a horrid hack in the driver core, just because of some
really bad drivers, is not ok, that's an interface _I_ will have to
support for the next few decades.

And it's going to take you a while to get something like this ever
merged in anyway, odds are you can fix up the driver faster...

> > The cxgb4: driver is an example where although I did propose patches
> > to use asynch firmware loading the entire registration of the
> > netdevice would need to be changed as well in order to get this right.
> > In short we have to scramble now to first identify drivers that have
> > long init sequences and then fix. There's an assumption that we can
> > easily fix drivers, this can take time. This series, although does
> > take advantage of a kernel interface for other uses, lets us identify
> > these drivers on the kernel ring buffer, so we can go and address
> > fixing them with time.
> 
> Another thing that came up during asynch firmware review / integration
> on cxgb4 was that it would not be the only thing that would need to be
> fixed, the driver also has a ton of ports and at least as per my
> review the proper fix would be to use platform regiister stuff. It is
> a major rewrite of the driver but an example of a driver that needs
> quite a bit of work to meet this new 30 second driver requirement.

It shouldn't be using any platform driver stuff, it's a pci device, not
a platform device.

Why not just put the initial "register the device" in a single-shot
workqueue or thread or something like that so that modprobe returns
instantly back with a success and all is fine?

Again, trying to hack the "deferred init" logic for PCI drivers isn't
ok, I'm not going to take that into the driver core if at all possible,
sorry.

greg k-h
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