Message-ID: <20150902232249.GK8051@wotan.suse.de>
Date:	Thu, 3 Sep 2015 01:22:49 +0200
From:	"Luis R. Rodriguez" <mcgrof@...e.com>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	Arend van Spriel <arend@...adcom.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Ming Lei <ming.lei@...onical.com>,
	Takashi Iwai <tiwai@...e.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Liam Girdwood <liam.r.girdwood@...ux.intel.com>,
	"Jie, Yang" <yang.jie@...el.com>,
	"joonas.lahtinen@...ux.intel.com" <joonas.lahtinen@...ux.intel.com>,
	Tom Gundersen <teg@...m.no>, Al Viro <viro@...iv.linux.org.uk>,
	Kay Sievers <kay@...y.org>,
	David Woodhouse <dwmw2@...radead.org>,
	Luis Rodriguez <mcgrof@...not-panic.com>,
	lkml <linux-kernel@...r.kernel.org>,
	yalin wang <yalin.wang2010@...il.com>
Subject: Re: Problems loading firmware using built-in drivers with kernels
 that use initramfs.

On Wed, Sep 02, 2015 at 04:13:51PM -0700, Dmitry Torokhov wrote:
> On Wed, Sep 2, 2015 at 2:03 PM, Arend van Spriel <arend@...adcom.com> wrote:
> > On 09/02/2015 08:58 PM, Luis R. Rodriguez wrote:
> >>
> >> On Wed, Sep 02, 2015 at 02:13:49PM +0200, Arend van Spriel wrote:
> >>>
> >>> On 09/02/2015 02:09 PM, Arend van Spriel wrote:
> >>>>
> >>>> On 09/02/2015 03:19 AM, Luis R. Rodriguez wrote:
> >>>>>
> >>>>> On Mon, Aug 31, 2015 at 10:21:34PM +0800, Ming Lei wrote:
> >>>>>>
> >>>>>> On Sun, Aug 30, 2015 at 4:25 PM, Arend van Spriel
> >>>>>> <arend@...adcom.com> wrote:
> >>>>>>>
> >>>>>>> Does this mean a built-in driver can not get firmware from initramfs
> >>>>>>> or
> >>>>>>> built in the kernel early. Seems a bit too aggressive. The problem
> >>>>>>> stated in
> >>>>>>> this thread is when the firmware is not on initramfs but only on the
> >>>>>>> rootfs.
> >>>>>>
> >>>>>>
> >>>>>> Yes, strictly speaking, user mode request can't be handled with defer
> >>>>>> probe
> >>>>>> during booting because we don't know how the user helper handles the
> >>>>>> request,
> >>>>>
> >>>>>
> >>>>> FWIW I have a strategy in mind to help us compartamentalize the user
> >>>>> mode
> >>>>> helper only to the dell-rbu driver, and as such phase out that code
> >>>>> eventually
> >>>>> completely. Its part of the goals I have with the extensible firmware
> >>>>> API I've
> >>>>> been proposing.
> >>>>>
> >>>>>> that said even checking if the firmware exists in current path doesn't
> >>>>>> make sense for user mode request.
> >>>>>>
> >>>>>> So the patch should have used defer proble for direct load only
> >>>>>> during booting.
> >>>>>
> >>>>>
> >>>>> What exact guarantees would we be giving to callers if they follow up
> >>>>> on probe
> >>>>> with -EDEFER_PROBE ? I'd much prefer to try to avoid such uses in init
> >>>>> / probe
> >>>>> (note that unless you're using async probe since we batch both so it
> >>>>> doesn't really
> >>>>> matter where you place your code) all together and then for the few
> >>>>> remaining
> >>>>> stragglers understand the requirements and provide an interface that
> >>>>> lets them
> >>>>> claim their requirements and try to meets them.
> >>>>>
> >>>>> A grammatical hunt for drivers who call fw API on init / probe can be
> >>>>> completed, although I know the hunt needs a bit more fine tuning it
> >>>>> surely can
> >>>>> be completed. If we don't have many callers the compexity added for
> >>>>> only a
> >>>>> few callers with rather loose criteria seems rather unnecessary,
> >>>>> specially if
> >>>>> we can change the drivers and make these driver sthe exception rather
> >>>>> than
> >>>>> a norm.
> >>>>>
> >>>>> Then as for drivers *needing* the fw at probe why not have a proper
> >>>>> interface
> >>>>> that does guarantee they get the requirements they ask for first ? For
> >>>>> instance
> >>>>> a new probe type specified by the driver could enable the core to wait
> >>>>> for say
> >>>>> an event and then tirgger a probe, kind of how we ended up defining
> >>>>> the async
> >>>>> probe type preference:
> >>>>>
> >>>>> static struct some_bus_driver some_driver = {
> >>>>>          .probe = some_probe,
> >>>>>          .id_table = some_id,
> >>>>>          .driver = {
> >>>>>                  .name = DEVICE_NAME,
> >>>>>                  .pm = &some_pm_ops,
> >>>>>                  .probe_type = PROBE_PREFER_POST_FOO,
> >>>>>          },
> >>>>> };
> >>>>>
> >>>>> Then we just don't try just hoping for completion but rather can do
> >>>>> something
> >>>>> about the criteria passed.
> >>>
> >>>
> >>> So should the probe type indicate some event or should it just
> >>> indicate what the driver needs, ie. .probe_type =
> >>> PROBE_TYPE_NEED_FW.
> >>
> >>
> >> Right so this is an open question. I suggested something like the above
> >> since the deferred probe documentation on drivers/base/dd.c states:
> >>
> >>   * Sometimes driver probe order matters, but the kernel doesn't always
> >> have
> >>   * dependency information
> >>
> >> I'm alluding that we consider *avoiding* -EPROBE_DEFER for areas of the
> >> kernel where some work can be done to not only list the dependency
> >> the information from the driver but also we know we can get it from
> >> the kernel. In this case I do believe we could not only express the
> >> requirement but also wait for it in the kernel. Before we do that
> >> though I think it'd be good to do a grammar hunt to determine exactly
> >> how popular all this fw on probe needed really is.
> >
> >
> > Ok. So some background why we need it in brcm80211 drivers. So as a wireless
> > network device driver the answer we got when asking for an event to load
> > firware is upon IF_UP for a registered net device. Because we try to do
> > things smart we query the firmware running on the device for capabilities
> > before we can register the net device hence we request the firmware during
> > probe. This may be specific to wireless drivers (Intel has same approach if
> > not mistaken) but I suspect there may be more.
> 
> We have the same issue with input devices: before we can register one
> we need to set their capabilities and to know their capabilities we
> quite often need to load their firmware/config and query the device.

Should Arend's driver use async probe then?

IMHO its just as hacky as using -EPROBE_DEFER too, but its at least
preemptively hacky. Sadly I can't think of clear and clever way for the kernel
to know when firmware will be ready either...  Would userspace know? Should the
kernel learn this from userspace ?

For instance, if init is going to use initramfs it can pivot_root() and later
send us a smoke signal when done, and it it doesn't it can also send us a smoke
signal. In the absence of such a hint being implemented I suppose -EPROBE_DEFER,
async probe or a notifier on pivot_root() is best effort we can do, but again
*eh*.

  Luis
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