linux-kernel - Re: [PATCH v4 2/2] drivers: bus: Delete CONFIG_SIMPLE_PM

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Date:   Tue, 26 Oct 2021 23:19:50 +0530
From:   Amit Pundir <amit.pundir@...aro.org>
To:     Saravana Kannan <saravanak@...gle.com>
Cc:     Russell King <linux@...linux.org.uk>,
        Neil Armstrong <narmstrong@...libre.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Magnus Damm <magnus.damm@...il.com>,
        Tony Lindgren <tony@...mide.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Damien Le Moal <damien.lemoal@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Android Kernel Team <kernel-team@...roid.com>,
        linux-arm-kernel@...ts.infradead.org,
        lkml <linux-kernel@...r.kernel.org>, linux-oxnas@...ups.io,
        linux-renesas-soc@...r.kernel.org, linux-omap@...r.kernel.org,
        linux-riscv@...ts.infradead.org,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        John Stultz <john.stultz@...aro.org>
Subject: Re: [PATCH v4 2/2] drivers: bus: Delete CONFIG_SIMPLE_PM_BUS

On Tue, 26 Oct 2021 at 06:00, Saravana Kannan <saravanak@...gle.com> wrote:
>
> On Fri, Oct 22, 2021 at 10:00 AM Amit Pundir <amit.pundir@...aro.org> wrote:
> >
> > On Fri, 22 Oct 2021 at 05:13, Saravana Kannan <saravanak@...gle.com> wrote:
> > >
> > > On Thu, Oct 21, 2021 at 4:21 AM Amit Pundir <amit.pundir@...aro.org> wrote:
> > > >
> > > > Hi Saravana,
> > > >
> > > > This patch broke v5.15-rc6 on RB5 (sm8250 | qcom/qrb5165-rb5.dts).
> > > > I can't boot past this point https://www.irccloud.com/pastebin/raw/Nv6ZwHmW.
> > >
> > > Amit top posting? How did that happen? :)
> > >
> > > The fact you are seeing this issue is super strange though. The driver
> > > literally does nothing other than allowing some sync_state() callbacks
> > > to happen. I also grepped for the occurence of "simple-bus" in
> > > arch/arm64/boot/dts/qcom/ and the only instance for 8250 is for the
> > > soc node.
> > >
> > > The only thing I can think of is that without my patch some
> > > sync_state() callbacks weren't getting called and maybe it was masking
> > > some other issue.
> > >
> > > Can you try to boot with this log (see log patch below) and see if the
> > > device hangs right after a sync_state() callback? Also, looking at the
> > > different sync_state() implementations in upstream, I'm guessing one
> > > of the devices isn't voting for interconnect bandwidth when it should
> > > have.
> > >
> > > Another thing you could do is boot without the simple-bus changes and
> > > then look for all instances of "state_synced" in /sys/devices and then
> > > see if any of them has the value "0" after boot up is complete.
> >
> > Turned out RB5 is not even reaching up to
> > device_links_flush_sync_list() and seem to be stuck somewhere in
> > device_links_driver_bound(). So I added more print logs to narrow down
> > to any specific lock state but those additional prints seem to have
> > added enough delay to unblock that particular driver (Serial:
> > 8250/16550 driver if I understood the logs correctly) and I eventually
> > booted to UI.
>
> Ugh... I think I know what's going on. It popped into my head over the weekend.
>
> Couple of ways to confirm my theory:
> 1. After it finishes booting in both cases, can you compare the output
> of the command below? I'm expecting to see a significant drop in the
> number of device links.
> ls -l /sys/class/devlink | wc -l
>

On a successful boot with debug prints:
rb5:/ $ ls -l /sys/class/devlink | wc -l
245

Booting with this SIMPLE_PM_BUS patch reverted:
rb5:/ $ ls -l /sys/class/devlink | wc -l
248

> 2. Can you try out this terrible hack patch (not final fix, no code
> reviews please) on top of Tot to see if it fixes your issue without
> having to add hacky logs?
>

No luck booting with the following hack patch either.

Regards,
Amit Pundir


> Thanks,
> Saravana
>
> --- a/drivers/bus/simple-pm-bus.c
> +++ b/drivers/bus/simple-pm-bus.c
> @@ -38,10 +38,12 @@ static int simple_pm_bus_probe(struct platform_device *pdev)
>          * a device that has a more specific driver.
>          */
>         if (match && match->data) {
> -               if (of_property_match_string(np, "compatible",
> match->compatible) == 0)
> +               if (of_property_match_string(np, "compatible",
> match->compatible) == 0) {
> +                       of_platform_populate(np, NULL, lookup, &pdev->dev);
>                         return 0;
> -               else
> +               } else {
>                         return -ENODEV;
> +               }
>         }