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Subject: Re: [BUG 4.9] New led trigger usbport gets the kernel to panic
To: =?UTF-8?B?UmFmYcWCIE1pxYJlY2tp?= <zajec5@gmail.com>,
        Pavel Machek <pavel@ucw.cz>
Cc: Ralph Sennhauser <ralph.sennhauser@gmail.com>,
        "open list:LED SUBSYSTEM" <linux-leds@vger.kernel.org>,
        Richard Purdie <rpurdie@rpsys.net>,
        =?UTF-8?B?UmFmYcWCIE1pxYJlY2tp?= <rafal@milecki.pl>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "linux-usb@vger.kernel.org" <linux-usb@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
From: Jacek Anaszewski <j.anaszewski@samsung.com>
Message-id: <6c5ea183-4ef8-7524-034d-69fb388a3a7a@samsung.com>
Date: Thu, 08 Dec 2016 09:40:43 +0100
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Hi Rafał,

On 12/06/2016 06:29 PM, Rafał Miłecki wrote:
> On 6 December 2016 at 18:26, Pavel Machek <pavel@ucw.cz> wrote:
>> On Fri 2016-12-02 09:48:18, Ralph Sennhauser wrote:
>>> On Thu, 1 Dec 2016 17:56:07 +0100
>>> Rafał Miłecki <rafal@milecki.pl> wrote:
>>>
>>>> On 12/01/2016 03:28 PM, Ralph Sennhauser wrote:
>>>>> Below the oops with your debug patch applied.
>>>>>
>>>>> (...)
>>>>>
>>>>> root@wrt1900acs:/# cd sys/class/leds/pca963x\:shelby\:white\:usb2/
>>>>> root@wrt1900acs:/sys/devices/platform/soc/soc:internal-regs/f1011000.i2c/i2c-0/0-0068/leds/pca963x:shelby:white:usb2#
>>>>> echo usbport > trigger [  124.727665] leds
>>>>> pca963x:shelby:white:usb2: [usbport_trig_add_port] port:dd708240
>>>>> [  124.735266] leds pca963x:shelby:white:usb2:
>>>>> [usbport_trig_add_port] port->port_name:usb1-port1
>>>>> port->data:dd708140 [  124.745671] leds pca963x:shelby:white:usb2:
>>>>> [usbport_trig_add_port] port:dd7083c0 [  124.753194] leds
>>>>> pca963x:shelby:white:usb2: [usbport_trig_add_port]
>>>>> port->port_name:usb2-port1 port->data:dd708140 [  124.763594] leds
>>>>> pca963x:shelby:white:usb2: [usbport_trig_add_port] port:dd708300
>>>>> [  124.771114] leds pca963x:shelby:white:usb2:
>>>>> [usbport_trig_add_port] port->port_name:usb3-port1
>>>>> port->data:dd708140
>>>>> root@wrt1900acs:/sys/devices/platform/soc/soc:internal-regs/f1011000.i2c/i2c-0/0-0068/leds/pca963x:shelby:white:usb2#
>>>>> echo 1 > ports/usb2-port1[  171.649751] leds
>>>>> pca963x:shelby:white:usb2: [usbport_trig_port_store] buf:1
>>>>> [  171.649751]  size:2
>>>>>
>>>>> [  171.660160] leds pca963x:shelby:white:usb2:
>>>>> [usbport_trig_port_store] port:dd7083c0 [  171.668103] leds
>>>>> pca963x:shelby:white:usb2: [usbport_trig_port_store]
>>>>> port->port_name:usb2-port1 port->data:dd708140 [  171.678678]
>>>>> [usbport_trig_update_count] usbport_data->count:0 [  171.684457]
>>>>> [usbport_trig_update_count] usbport_data->count:0 [  171.690253]
>>>>> Unable to handle kernel NULL pointer dereference at virtual address
>>>>> 00000000
>>>>
>>>> Oh, so this happens a bit later than I expected or I could read from
>>>> the backtrace. Anyway this debugging was still helpful, I think I can
>>>> see a possible problem.
>>>>
>>>> So most likely the crash happens at the:
>>>> led_cdev->brightness_set(led_cdev, ...);
>>>> call. I'm not sure what I was thinking when writing that code. It
>>>> looks wrong.
>>>>
>>>> The thing is some LEDs (drivers) don't provide brightness_set op.
>>>> It's fine, we should just use brightness_set_blocking op when that
>>>> happens. Of course kernel has proper helpers for that, we don't have
>>>> to worry about the choice of op or scheduling the work. I have no
>>>> idea why I didn't use a proper helper in the first place.
>>>>
>>>> So we should simply replace above call with one of following ones:
>>>> 1) led_set_brightness(led_cdev, ...);
>>>> 2) led_set_brightness_nosleep(led_cdev, ...);
>>>> 3) led_set_brightness_sync(led_cdev, ...);
>>>>
>>>> I still have to check which one is correct. In theory we don't deal
>>>> blinking at this point so we shouldn't need to use led_set_brightness.
>>>>
>>>> led_set_brightness_nosleep looks like the most likely correct choice.
>>>>
>>>> led_set_brightness_sync requires brightness_set_blocking which is not
>>>> always present so most likely we don't want this one.
>>>>
>>>>
>>>> If you have some free time and you want to play with this, please
>>>> replace led_cdev->brightness_set
>>>> with
>>>> led_set_brightness_nosleep
>>>> and give it a try. This should fix crashes for you.
>>>>
>>>> I'll look at this again during next days.
>>>
>>> Hi Rafał
>>>
>>> I just gave 2) led_set_brightness_nosleep a try. The kernel no longer
>>> crashes and the led does work as expected.
>>
>> Do you have any patch that needs to be applied?
>
> Yes, it has been pushed:
> https://git.kernel.org/cgit/linux/kernel/git/gregkh/usb.git/commit/?h=usb-next&id=89778ba335e302a450932ce5b703c1ee6216e949
>
> When sending it I didn't Cc linux-leds as get_maintainer.pl didn't
> pick it. Should we add MAINTAINERS entry for ledtrig-usbport.c maybe?
>

I haven't tested this trigger earlier, probably due to the fact that
it was targeted for usb subsystem, sorry about that. Nonetheless,
I've just tried it on exynos4412-trats2 board and it seems not to
work properly.

I have the board connected through USB (I have an opened ssh session),
I'm doing "echo usbport > trigger", then I can see the "ports"
directory, but it is empty.

Any ideas on the possible reasons? Exynos4412-trats2 uses
Ethernet Gadget (with CDC Ethernet support) USB Gadget Driver
for USB networking.

-- 
Best regards,
Jacek Anaszewski