linux-kernel - Re: [PATCH v2 2/5] firmware: annotate thou shalt not request fw on init or probe

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Date:   Sat, 3 Sep 2016 01:59:16 +0200
From:   "Luis R. Rodriguez" <mcgrof@...nel.org>
To:     "Luis R. Rodriguez" <mcgrof@...nel.org>
Cc:     Daniel Vetter <daniel.vetter@...ll.ch>,
        Felix Fietkau <nbd@....name>,
        David Woodhouse <dwmw2@...radead.org>,
        Jörg Rödel <jroedel@...e.de>,
        Joerg Roedel <joro@...tes.org>,
        Roman Pen <r.peniaev@...il.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Ming Lei <ming.lei@...onical.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Marek <mmarek@...e.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Vikram Mulukutla <markivx@...eaurora.org>,
        Stephen Boyd <stephen.boyd@...aro.org>,
        zohar@...ux.vnet.ibm.com, Mark Brown <broonie@...nel.org>,
        Takashi Iwai <tiwai@...e.de>,
        Johannes Berg <johannes@...solutions.net>,
        Christian Lamparter <chunkeey@...glemail.com>,
        hauke@...ke-m.de, Josh Boyer <jwboyer@...oraproject.org>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>, jslaby@...e.com,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andy Lutomirski <luto@...capital.net>,
        Wu Fengguang <fengguang.wu@...el.com>, rpurdie@...ys.net,
        j.anaszewski@...sung.com, Abhay_Salunke@...l.com,
        Julia Lawall <Julia.Lawall@...6.fr>, Gilles.Muller@...6.fr,
        nicolas.palix@...g.fr, Tom Gundersen <teg@...m.no>,
        David Howells <dhowells@...hat.com>,
        Alessandro Rubini <rubini@...dd.com>,
        Kevin Cernekee <cernekee@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Jonathan Corbet <corbet@....net>,
        Thierry Martinez <martinez@...p.org>, cocci@...teme.lip6.fr,
        linux-serial@...r.kernel.org, linux-doc@...r.kernel.org,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH v2 2/5] firmware: annotate thou shalt not request fw on
 init or probe

On Thu, Aug 25, 2016 at 09:41:33PM +0200, Luis R. Rodriguez wrote:
> On Thu, Aug 25, 2016 at 01:05:44PM +0200, Daniel Vetter wrote:
> > On Wed, Aug 24, 2016 at 10:39 PM, Luis R. Rodriguez <mcgrof@...nel.org> wrote:
> > Some users want a fully running gfx stack 2s after power-on. There's
> > not even enough time to load an uefi or vga driver first. i915
> > directly initializes the gpu from power-on state on those.
> 
> I see.. thanks.
> 
> > >> I think what would work is loading the different subsystems of the
> > >> driver in parallel (we already do that largely)
> > >
> > > Init level stuff is actually pretty synchronous, and in fact both
> > > init and probe are called serially. There are a few subsystems which
> > > have been doing things a bit differently, but these are exceptions.
> > >
> > > When you say we already do this largely, can you describe a bit more
> > > precisely what you mean ?
> > 
> > Oh, this isn't subsystems as in linux device/driver model, but
> > different parts within the driver. We fire up a bunch of struct work
> > to get various bits done asynchronously.
> 
> Thanks for the clarification.

<-- snip -->

> > One of the proposals which would have worked for us died a while back:
> > 
> > https://lkml.org/lkml/2014/6/15/47
> 
> Interesting, the problem stated here, which comes from the fact (as clarified
> above) the rootfs comes up only *after* we run do_initcalls() as such there are
> possible theoretical races even with request_firmware_nowait() -- as such that
> justifies even more the SmPL grammar rule to include even request_firmware_nowait()
> on probe / init as this patch has.
> 
> Anyway yeah that patch has good intentions but its wrong for a slew of reasons.
> The problem is the same as discussed with Bjorn recently. The solution
> discussed is that since only userspace knows when the *real* rootfs is ready
> (because of slew of reasons) the best we can do is have an event issued by
> userspace to inform us of that.

OK I have something I think we can build upon for this. Will send RFC.

  Luis