Re: [patch 5/6] Convert to use mutexes instead of semaphores

[Richard Purdie <rpurdie@rpsys.net>]

On Fri, 2006-08-11 at 08:58 -0400, Dmitry Torokhov wrote:
> On 8/11/06, Dmitry Torokhov <dtor@insightbb.com> wrote:
> > Backlight: convert to use mutexes instead of semaphores
> >
> 
> Apparently I missed that several drivers also use bd->sem so they need
> to be converted too... But what is it with the drivers:
> 
> static void aty128_bl_set_power(struct fb_info *info, int power)
> {
>         mutex_lock(&info->bl_mutex);
>         up(&info->bl_dev->sem);
>         info->bl_dev->props->power = power;
>         __aty128_bl_update_status(info->bl_dev);
>         down(&info->bl_dev->sem);
>         mutex_unlock(&info->bl_mutex);
> }
> 
> Why we are doing up() before down()??? And it is in almost every
> driver that uses backlight... Do I need more coffee? [CC-ing bunch of
> people trying to get an answer...]

It looks totally wrong.

In the archives, there are a number of comments from me questioning
whether that driver needs to touch bl_dev->sem anyway (esp. given the
mutex as well). I never did find out what it was trying to protect
against...

Richard