On Tue, Aug 18, 2015 at 01:53:27PM +0200, Sebastian Hesselbarth wrote: > On 08/18/2015 01:38 PM, Antoine Tenart wrote: > >+ val = berlin_pwm_readl(pwm, pwm_dev->hwpwm, BERLIN_PWM_CONTROL); > >+ val &= ~BERLIN_PWM_PRESCALE_MASK; > >+ val |= prescale; > >+ berlin_pwm_writel(val, pwm, pwm_dev->hwpwm, BERLIN_PWM_CONTROL); > >+ > >+ berlin_pwm_writel(duty, pwm, pwm_dev->hwpwm, BERLIN_PWM_DUTY); > >+ berlin_pwm_writel(period, pwm, pwm_dev->hwpwm, BERLIN_PWM_TCNT); > > The reason why I usually tend to _not_ use _relaxed() in low-performance > setup code is that you'll have to think about reordering issues when > using _relaxed ones.
If that is your concern, then you should read Documentation/memory-barriers.txt, specifically the section on "ACQUIRES VS I/O ACCESSES". Using the non- relaxed accessors doesn't save you in every circumstance. > The question here is: Is it _guaranteed_ that above writel_relaxed() > will be issued _before_ actually releasing the spin_lock? There is no guarantee on all hardware that writel() will be seen by the hardware before other accesses within a separate spinlocked region using the same lock. -- FTTC broadband for 0.8mile line: currently at 10.5Mbps down 400kbps up according to speedtest.net. -- To unsubscribe from this list: send the line "unsubscribe linux-pwm" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
