linux-kernel - Re: [PATCH v2] leds: USB: Add support for MSI GT683R led panels

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Date:	Mon, 9 Jun 2014 13:42:22 +0200
From:	Johan Hovold <johan@...nel.org>
To:	Janne Kanniainen <janne.kanniainen@...il.com>
Cc:	Johan Hovold <johan@...nel.org>, Bryan Wu <cooloney@...il.com>,
	rpurdie@...ys.net, linux-kernel@...r.kernel.org,
	linux-leds@...r.kernel.org, linux-usb@...r.kernel.org,
	Jiri Kosina <jkosina@...e.cz>, linux-input@...r.kernel.org
Subject: Re: [PATCH v2] leds: USB: Add support for MSI GT683R led panels

On Sat, Jun 07, 2014 at 01:12:39PM +0300, Janne Kanniainen wrote:
> > First of all, please reply to the original thread and make sure to not
> > drop people or lists from CC.
> 
> Sorry this is my first patch and i didn't know that. Now I know.
> 
> > For arrays you can use the ARRAY_SIZE() macro if that was the reason for
> > this change. I should have mentioned that when I pointed out that you
> > cannot use strlen().
> 
> That wasn't the reason. I just thought it might be better to use u64
> than char[8]. I know why I can't use strlen and that was only careless
> error. And there was lot of them :( I will be more careful next time.

No problem, that's what review is for, and the second version was much
cleaner even if there were still a few issues (some hard to know about,
such as the DMA from stack issue, which is also a very common error).

> > Where did you get these (HID report) values from by the way?
> 
> I got them by reverse engineering.

Traffic sniffing?

> >> +
> >> +static void gt683r_brightness_set(struct led_classdev *led_cdev,
> >> +                               enum led_brightness brightness)
> >> +{
> >> +     struct gt683r_led *led =
> >> +                     container_of(led_cdev, struct gt683r_led, led_dev);
> >> +
> >> +     mutex_lock(&led->lock);
> >
> > You cannot grab a mutex here since this function can be called from
> > interrupt context (if I remember correctly). Either way, you shouldn't
> > be holding the lock until the work task has finished...
> 
> I thought use asked me to put some lock there:
> 
> >> +
> >> +static void gt683r_brightness_set(struct led_classdev *led_cdev,
> >> +                               enum led_brightness brightness)
> >> +{
> >> +     struct gt683r_led *led =
> >> +                     container_of(led_cdev, struct gt683r_led, led_dev);
> >> +
> >> +     led->brightness = brightness;
> >
> > Missing locking?

I asked if locking was missing and did not specify how you should be
adding it. ;)

In fact, it seems you can get away with not adding any locking here.
Just do the (mutex) locking in gt683r_led_set (or gt683r_led_work).

Johan
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