From mboxrd@z Thu Jan 1 00:00:00 1970 From: thierry.reding@avionic-design.de (Thierry Reding) Date: Fri, 14 Dec 2012 07:48:05 +0100 Subject: clock_enable mismatches in pwm-backlight/pwm_enable In-Reply-To: <1355428233.2159.15.camel@gitbox> References: <1355428233.2159.15.camel@gitbox> Message-ID: <20121214064805.GA24094@avionic-0098.adnet.avionic-design.de> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Fri, Dec 14, 2012 at 08:50:33AM +1300, Tony Prisk wrote: > Hi Thierry, > > This works out quite well with you looking after pwm and pwm-backlight. > > I noticed while troubleshooting pwm on arch-vt8500 last night that the > clk_enable count was getting huge for no obvious reason, and I narrowed > it down to the pwm-backlight driver. > > in pwm-bl.c::pwm_backlight_update_status() > > if (brightness == 0) { > pwm_config(pb->pwm, 0, pb->period); > pwm_disable(pb->pwm); > } else { > ... > pwm_config(pb->pwm, duty_cycle, pb->period); > pwm_enable(pb->pwm); > } > > Which looks fine on its own, except that in pwm_enable() it's not > uncommon to have clk_enable calls. > > What happens is everytime the backlight level is changed to anything > except 0, pwm_enable() is called, which calls clk_enable() and the > counter goes up. Only when brightness=0 does pwm_disable() get called > and the accompanying clk_disable(). > > If you change brightness 3-4 times, then set brightness=0, the clock is > enable 3-4 times, but only disabled 1. > > At first I thought it was my bad, but it seems Tegra and IMX suffer from > this problem as well - they both do clk_ calls in pwm_enable - which > doesn't seem unreasonable. > > Any thoughts on how this could be rectified? What you describe above should not happen. If you look at the core code, you'll see that pwm_enable() and pwm_disable() keep track of the enable status of PWM devices and only call the driver's .enable() or .disable() if it is actually needed. I've just checked the pwm-vt8500 driver and it looks like clk_enable() and clk_disable() are properly balanced everywhere, so I can't explain why this would happen. Thierry -------------- next part -------------- A non-text attachment was scrubbed... Name: not available Type: application/pgp-signature Size: 836 bytes Desc: not available URL: