Pin configuration conflict and NULL pointer dereference on RPi 3

[Eric Anholt]

Stefan Wahren <stefan.wahren at i2se.com> writes:

> Hi Gerd,
>
>> Gerd Hoffmann <kraxel at redhat.com> hat am 2. Juni 2016 um 18:07 geschrieben:
>> 
>> 
>> On Do, 2016-06-02 at 11:31 +0200, Gerd Hoffmann wrote:
>> >   Hi,
>> > 
>> > > > Patches 20-32 are for the wifi.  Mostly from Eric's bcm2837-wireless
>> > > > branch.  They clearly need some more love, but do the job for now.
>> > > 
>> > > I just came up with a fix that should replace patch #29, which means
>> > > I'll trust the expander stuff a lot more.  With the expander working,
>> > > you should be able to use pin 4 on it for HDMI hotplug detect, at which
>> > > point graphics should work.
>> > 
>> > Tried that.  i2c not working.  There seems to be a disagreement who owns
>> > gpio pin 45:
>> > 
>> > [root at pi-three linux]# dmesg | grep i2c
>> > [    2.354380] i2c /dev entries driver
>> > [    3.496734] pinctrl-bcm2835 3f200000.gpio: pin gpio45 already
>> > requested by 3f20c000.pwm; cannot claim for 3f205000.i2c
>> > [    3.512506] pinctrl-bcm2835 3f200000.gpio: pin-45 (3f205000.i2c)
>> > status -22
>> > [    3.540488] i2c-bcm2835 3f205000.i2c: Error applying setting, reverse
>> > things back
>> > [    4.551683] i2c-bcm2835 3f205000.i2c: i2c transfer timed out
>> > [    4.574599] i2c-bcm2835 3f805000.i2c: Could not read clock-frequency
>> > property
>> 
>> Tried to disable pwm in dt:
>> 
>>    -       status = "okay";
>>    +       status = "disabled";
>> 
>> Now i2c is happy, and fxl6408 seems to work too:
>> 
>>    [root at pi-two ~]# dmesg | grep -i FXL6408
>>    [    3.580660] fxl6408 0-0043: FXL6408 probe returned DID: 0x87
>> 
>
> i stumbled yesterday on this patch [1] which is related to this (still open) issue. I wrote to the patch author and he said that sometimes the i2c-bcm2835 on his RPi 3 (Aarch64 Kernel) crashed with a NULL pointer dereference. He also said that the random I2C timeouts like above
>
> i2c-bcm2835 3f805000.i2c: i2c transfer timed out
>
> still occurs. Also reported here [2].
>
> Can you confirm any of these issues (requires PWM_BCM2835 and I2C_BCM2835 enabled)?
>
> I've the suspicion that the unexpected interrupts are triggered by the pin muxing conflict at pin 45. Please refer to the firmware DT blob [3].
>
> In order to fix the NULL pointer dereference i suggest the following:

Just a reminder: This FXL6408 driver will not be usable on the Raspberry
Pi.  On Pi3, the firmware is looping hitting the only I2C controller
that can talk to the pins attached to the FXL6408 (for its undervoltage
detection).  If Linux tries to drive that controller on its own,
everything will go wrong.
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