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Date:   Thu, 6 Aug 2020 20:02:18 -0700
From:   Saravana Kannan <saravanak@...gle.com>
To:     John Stultz <john.stultz@...aro.org>
Cc:     Bjorn Andersson <bjorn.andersson@...aro.org>,
        Steev Klimaszewski <steev@...i.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Marc Zyngier <maz@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Andy Gross <agross@...nel.org>,
        Android Kernel Team <kernel-team@...roid.com>,
        lkml <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Hanks Chen <hanks.chen@...iatek.com>,
        CC Hwang <cc.hwang@...iatek.com>,
        Loda Chou <loda.chou@...iatek.com>,
        Thierry Reding <thierry.reding@...il.com>
Subject: Re: [PATCH v3 2/4] irqchip/qcom-pdc: Switch to using
 IRQCHIP_PLATFORM_DRIVER helper macros

On Thu, Aug 6, 2020 at 7:49 PM John Stultz <john.stultz@...aro.org> wrote:
>
> On Thu, Aug 6, 2020 at 6:42 PM Bjorn Andersson
> <bjorn.andersson@...aro.org> wrote:
> > On Thu 06 Aug 18:22 PDT 2020, John Stultz wrote:
> > > On Thu, Aug 6, 2020 at 5:43 PM Bjorn Andersson
> > > <bjorn.andersson@...aro.org> wrote:
> > > > On Wed 05 Aug 14:57 PDT 2020, John Stultz wrote:
> > > > > On Wed, Aug 5, 2020 at 2:47 PM Steev Klimaszewski <steev@...i.org> wrote:
> > > > > > On 8/5/20 4:16 PM, Steev Klimaszewski wrote:
> > > > > > > On 8/5/20 3:19 PM, Saravana Kannan wrote:
> > > > > > >> On Wed, Aug 5, 2020 at 12:44 AM John Stultz <john.stultz@...aro.org> wrote:
> > > > > > >>> <sigh>
> > > > > > >>> So this is where I bashfully admit I didn't get a chance to try this
> > > > > > >>> patch series out, as I had success with a much older version of
> > > > > > >>> Saravana's macro magic.
> > > > > > >>>
> > > > > > >>> But unfortunately, now that this has landed in mainline, I'm seeing
> > > > > > >>> boot regressions on db845c. :( This is in the non-modular case,
> > > > > > >>> building the driver in.
> > > > > > >> Does that mean the modular version is working? Or you haven't tried
> > > > > > >> that yet? I'll wait for your reply before I try to fix it. I don't
> > > > > > >> have the hardware, but it should be easy to guess this issue looking
> > > > > > >> at the code delta.
> > > > > > > For what it's worth, I saw this too on the Lenovo C630 (started on -next
> > > > > > > around 20200727, but I didn't track it down as, well, there's less way
> > > > > > > to get debug output on the C630.
> > > > > > >
> > > > > > > In my testing, module or built-in doesn't matter, but reverting does
> > > > > > > allow me to boot again.
> > > > > > >
> > > > > > Actually - I spoke too soon - QCOM_PDC built-in with the commit reverted
> > > > > > boots, however, module (on the c630 at least) doesn't boot whether it's
> > > > > > a module or built-in.
> > > > >
> > > > > You may need to set deferred_probe_timeout=30 to give things a bit
> > > > > more grace time to load.
> > > >
> > > > With the risk of me reading more into this than what you're saying,
> > > > please don't upstream anything that depend this parameter to be
> > > > increased.
> > > >
> > > > Compiling any of these drivers as module should not require the user to
> > > > pass additional kernel command line parameters in order to get their
> > > > device to boot.
> > >
> > > So, ideally I agree, and Saravana's fw_devlink work should allow us to
> > > avoid it. But the reality is that it is already required (at least in
> > > configurations heavily using modules) to give more time for modules
> > > loaded to resolve missing dependencies after init begins (due to
> > > changes in the driver core to fail loading after init so that optional
> > > dt links aren't eternally looked for). This was seen when trying to
> > > enable the qualcom clk drivers to modules.
> > >
> >
> > So to clarify what you're saying, any system that boots successfully
> > with the default options is a sign of pure luck - regardless of being
> > builtin or modules.
> >
> >
> > And there you have my exact argument against the deferred timeout magic
> > going on in the driver core. But as you know people insist that it's
> > more important to be able to boot some defunct system from NFS than a
> > properly configured one reliably.
>
> I'd agree, but the NFS case was in use before, and when the original
> deferred timeout/optional link handling stuff landed no one complained
> they were broken by it (at least at the point where it landed). Only
> later when we started enabling more lower-level core drivers as
> modules did the shortened dependency resolution time start to bite
> folks.  My attempt to set the default to be 30 seconds helped there,
> but caused trouble and delays for the NFS case, and "don't break
> existing users" seemed to rule, so I set the default timeout back to
> 0.
>
> > > It doesn't seem necessary in this case, but I suggested it here as
> > > I've got it enabled by default in my AOSP builds so that the
> > > module-heavy configs for GKI boot properly (even if Saravana's
> > > fw_devlink work is disabled).
> > >
> >
> > With all due respect, that's your downstream kernel, the upstream kernel
> > should not rely on luck, out-of-tree patches or kernel parameters.
>
> I agree that would be preferred. But kernel parameters are often there
> for these sorts of cases where we can't always do the right thing.  As
> for out-of-tree patches, broken things don't get fixed until
> out-of-tree patches are developed and upstreamed, and I know Saravana
> is doing exactly that, and I hope his fw_devlink work helps fix it so
> the module loading is not just a matter of luck.

Btw, the only downstream fw_devlink change is setting itto =on (vs
=permissive in upstream).

> Also I think Thierry's comments in the other thread today are also
> good ideas for ways to better handle the optional dt link handling
> (rather than using a timeout).

Could you please give me a lore link to this thread? Just curious.

-Saravana

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