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References: <20190824132846.8589-1-u.kleine-koenig@pengutronix.de>
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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Tue, 17 Sep 2019 11:40:25 +0200
Message-ID: <CAMuHMdV+pwoAA0zH_vQf2nKqzrgHP8rcMStyJbnuu2qviFC_qg@mail.gmail.com>
Subject: Re: [PATCH v1 2/2] of: Let of_for_each_phandle fallback to
 non-negative cell_count
To:     Rob Herring <robh@kernel.org>,
        =?UTF-8?Q?Uwe_Kleine=2DK=C3=B6nig?= 
        <u.kleine-koenig@pengutronix.de>
Cc:     "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@vger.kernel.org>, Will Deacon <will@kernel.org>,
        Joerg Roedel <joro@8bytes.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux IOMMU <iommu@lists.linux-foundation.org>,
        linux-mediatek@lists.infradead.org,
        Sascha Hauer <kernel@pengutronix.de>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        Frank Rowand <frowand.list@gmail.com>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Robin Murphy <robin.murphy@arm.com>,
        Wolfram Sang <wsa+renesas@sang-engineering.com>,
        Linux I2C <linux-i2c@vger.kernel.org>,
        Linux-Renesas <linux-renesas-soc@vger.kernel.org>
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Hi Rob, Uwe,

On Fri, Sep 13, 2019 at 11:58 PM Rob Herring <robh@kernel.org> wrote:
> On Sat, 24 Aug 2019 15:28:46 +0200, =?UTF-8?q?Uwe=20Kleine-K=C3=B6nig?=          wrote:
> > Referencing device tree nodes from a property allows to pass arguments.
> > This is for example used for referencing gpios. This looks as follows:
> >
> >       gpio_ctrl: gpio-controller {
> >               #gpio-cells = <2>
> >               ...
> >       }
> >
> >       someothernode {
> >               gpios = <&gpio_ctrl 5 0 &gpio_ctrl 3 0>;
> >               ...
> >       }
> >
> > To know the number of arguments this must be either fixed, or the
> > referenced node is checked for a $cells_name (here: "#gpio-cells")
> > property and with this information the start of the second reference can
> > be determined.
> >
> > Currently regulators are referenced with no additional arguments. To
> > allow some optional arguments without having to change all referenced
> > nodes this change introduces a way to specify a default cell_count. So
> > when a phandle is parsed we check for the $cells_name property and use
> > it as before if present. If it is not present we fall back to
> > cells_count if non-negative and only fail if cells_count is smaller than
> > zero.
> >
> > Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>

This is now commit e42ee61017f58cd9 ("of: Let of_for_each_phandle fallback
to non-negative cell_count") in robh/for-next, which causes a lock-up when
booting a shmobile_defconfig kernel on r8a7791/koelsch:

rcu: INFO: rcu_sched self-detected stall on CPU
rcu:     0-....: (2099 ticks this GP) idle=6fe/1/0x40000002
softirq=29/29 fqs=1050
 (t=2100 jiffies g=-1131 q=0)
NMI backtrace for cpu 0
CPU: 0 PID: 1 Comm: swapper/0 Not tainted
5.3.0-rc2-shmobile-00050-ge42ee61017f58cd9 #376
Hardware name: Generic R-Car Gen2 (Flattened Device Tree)
[<c010f8ac>] (unwind_backtrace) from [<c010b620>] (show_stack+0x10/0x14)
[<c010b620>] (show_stack) from [<c073d038>] (dump_stack+0x7c/0x9c)
[<c073d038>] (dump_stack) from [<c0742e80>] (nmi_cpu_backtrace+0xa0/0xb8)
[<c0742e80>] (nmi_cpu_backtrace) from [<c0742f1c>]
(nmi_trigger_cpumask_backtrace+0x84/0x114)
[<c0742f1c>] (nmi_trigger_cpumask_backtrace) from [<c017d684>]
(rcu_dump_cpu_stacks+0xac/0xc8)
[<c017d684>] (rcu_dump_cpu_stacks) from [<c017a598>]
(rcu_sched_clock_irq+0x2ac/0x6b4)
[<c017a598>] (rcu_sched_clock_irq) from [<c0183980>]
(update_process_times+0x30/0x5c)
[<c0183980>] (update_process_times) from [<c01941a8>]
(tick_nohz_handler+0xcc/0x120)
[<c01941a8>] (tick_nohz_handler) from [<c05b1d40>]
(arch_timer_handler_virt+0x28/0x30)
[<c05b1d40>] (arch_timer_handler_virt) from [<c016c9e0>]
(handle_percpu_devid_irq+0xe8/0x21c)
[<c016c9e0>] (handle_percpu_devid_irq) from [<c0167a8c>]
(generic_handle_irq+0x18/0x28)
[<c0167a8c>] (generic_handle_irq) from [<c0167b3c>]
(__handle_domain_irq+0xa0/0xb4)
[<c0167b3c>] (__handle_domain_irq) from [<c03673ec>] (gic_handle_irq+0x58/0x90)
[<c03673ec>] (gic_handle_irq) from [<c0101a8c>] (__irq_svc+0x6c/0x90)
Exception stack(0xeb08dd30 to 0xeb08dd78)
dd20:                                     c0cc7514 20000013 00000005 00003b27
dd40: eb7c4020 c0cc750c 00000051 00000051 20000013 c0c66b08 eb1cdc00 00000018
dd60: 00000000 eb08dd80 c05c1a38 c0756c00 20000013 ffffffff
[<c0101a8c>] (__irq_svc) from [<c0756c00>]
(_raw_spin_unlock_irqrestore+0x1c/0x20)
[<c0756c00>] (_raw_spin_unlock_irqrestore) from [<c05c1a38>]
(of_find_node_by_phandle+0xcc/0xf0)
[<c05c1a38>] (of_find_node_by_phandle) from [<c05c1bb8>]
(of_phandle_iterator_next+0x68/0x178)
[<c05c1bb8>] (of_phandle_iterator_next) from [<c05c22bc>]
(of_count_phandle_with_args+0x5c/0x7c)
[<c05c22bc>] (of_count_phandle_with_args) from [<c053fc38>]
(i2c_demux_pinctrl_probe+0x24/0x1fc)
[<c053fc38>] (i2c_demux_pinctrl_probe) from [<c04463c4>]
(platform_drv_probe+0x48/0x94)
[<c04463c4>] (platform_drv_probe) from [<c0444a20>] (really_probe+0x1f0/0x2b8)
[<c0444a20>] (really_probe) from [<c0444e68>] (driver_probe_device+0x140/0x158)
[<c0444e68>] (driver_probe_device) from [<c0444ff0>]
(device_driver_attach+0x44/0x5c)
[<c0444ff0>] (device_driver_attach) from [<c04450b4>]
(__driver_attach+0xac/0xb4)
[<c04450b4>] (__driver_attach) from [<c0443178>] (bus_for_each_dev+0x64/0xa0)
[<c0443178>] (bus_for_each_dev) from [<c04438a8>] (bus_add_driver+0x148/0x1a8)
[<c04438a8>] (bus_add_driver) from [<c0445ad0>] (driver_register+0xac/0xf0)
[<c0445ad0>] (driver_register) from [<c0b010b0>] (do_one_initcall+0xa8/0x1d4)
[<c0b010b0>] (do_one_initcall) from [<c0b01448>]
(kernel_init_freeable+0x26c/0x2c8)
[<c0b01448>] (kernel_init_freeable) from [<c0751c70>] (kernel_init+0x8/0x10c)
[<c0751c70>] (kernel_init) from [<c01010e8>] (ret_from_fork+0x14/0x2c)
Exception stack(0xeb08dfb0 to 0xeb08dff8)
dfa0:                                     00000000 00000000 00000000 00000000
dfc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
dfe0: 00000000 00000000 00000000 00000000 00000013 00000000

Presumably it loops forever, due to a conversion of -1 to unsigned
somewhere?

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds