[PATCH 30/31] ARM: shmobile: r8a7791: add USB-DMAC device nodes

[Geert Uytterhoeven]

Hi Shimoda-san,

On Wed, Sep 30, 2015 at 11:06 AM, Yoshihiro Shimoda
<yoshihiro.shimoda.uh at renesas.com> wrote:
>> Sent: Wednesday, September 30, 2015 7:35 AM
>>     When the USB-DMAC driver is enabled, this causes kernel oops on at least
>> the R8A7791 Henninger/Porter boards (haven't checked the others yet) with
>> renesas-devel-20150928-v4.3-rc3 and even earlier tag. The oops can only be
>> seen with the earlyprintk=serial kernel parameter, otherwise the kernel just
>> hangs with a blank console.
>>
>> Unable to handle kernel NULL pointer dereference at virtual address 00000014

>> [<c027f0cc>] (usb_dmac_chan_halt) from [<c027f1c8>] (usb_dmac_runtime_suspend+0)
>>   r5:eebdaf50 r4:00000001
>> [<c027f19c>] (usb_dmac_runtime_suspend) from [<c02d60e0>] (pm_generic_runtime_s)
>>   r6:00000000 r5:c02ddfc4 r4:ee93d810 r3:c027f19c

> I'm not sure but I am guessing this issue related runtime PM? (suspend)
> I checked the usb-dmac driver roughly, and if the usb_dmac_runtime_suspend()
> is called before usb_dmac_chan_probe() runs, it might happen because dmac->iomem is NULL.

That's exactly what's happening. Reproduced with CONFIG_PREEMPT=y (thanks
Sergei), and patch sent.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at 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