| Message ID | 1481528409-5182-1-git-send-email-hofrat@osadl.org (mailing list archive) |
|---|---|
| State | Accepted, archived |
| Delegated to: | Stephen Boyd |
| Headers | show |
On Mon, Dec 12, 2016 at 08:40:09AM +0100, Nicholas Mc Guire wrote: > The delay here is not in atomic context and does not seem critical with > respect to precision, but usleep_range(min,max) with min==max results in > giving the timer subsystem no room to optimize uncritical delays. Fix > this by setting the range to 2000,3000 us. > > Fixes: commit f05259a6ffa4 ("clk: wm831x: Add initial WM831x clock driver") > Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org> > --- Yeah looks fine waiting longer for the FLL to lock won't cause any issues. Acked-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com> Thanks, Charles -- To unsubscribe from this list: send the line "unsubscribe linux-clk" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 12/12, Nicholas Mc Guire wrote: > The delay here is not in atomic context and does not seem critical with > respect to precision, but usleep_range(min,max) with min==max results in > giving the timer subsystem no room to optimize uncritical delays. Fix > this by setting the range to 2000,3000 us. > > Fixes: commit f05259a6ffa4 ("clk: wm831x: Add initial WM831x clock driver") > Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org> > --- Applied to clk-next
diff --git a/drivers/clk/clk-wm831x.c b/drivers/clk/clk-wm831x.c index f4fdac5..fe42d46 100644 --- a/drivers/clk/clk-wm831x.c +++ b/drivers/clk/clk-wm831x.c @@ -97,7 +97,8 @@ static int wm831x_fll_prepare(struct clk_hw *hw) if (ret != 0) dev_crit(wm831x->dev, "Failed to enable FLL: %d\n", ret); - usleep_range(2000, 2000); + /* wait 2-3 ms for new frequency taking effect */ + usleep_range(2000, 3000); return ret; }
The delay here is not in atomic context and does not seem critical with respect to precision, but usleep_range(min,max) with min==max results in giving the timer subsystem no room to optimize uncritical delays. Fix this by setting the range to 2000,3000 us. Fixes: commit f05259a6ffa4 ("clk: wm831x: Add initial WM831x clock driver") Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org> --- problem was located by coccinelle spatch The problem is that usleep_range is calculating the delay by exp = ktime_add_us(ktime_get(), min) delta = (u64)(max - min) * NSEC_PER_USEC so delta is set to 0 and then calls schedule_hrtimeout_range(exp, 0,...) effectively this means that the clock subsystem has no room to optimize and the behavior is no better than using usleep(). As this is not a critical delay it is set to a range of 2 to 3 milliseconds - this change needs a review by someone that knows the details of the device though. Q:It might actually be possible to just use msleep(2) here rather than using a hrtimer, at least I do not see what a hrtimer would be needed here for - a longer delay e.g. on a HZ100 box should not hurt ? Patch was only compile tested with: i386_defconfig + CONFIG_X86_INTEL_QUARK=y CONFIG_MFD_WM831X_I2C=y, COMMON_CLK=y, CONFIG_COMMON_CLK_WM831X=m Patch is against: 4.9.0-rc8 (localversion-next is -next-20161209) drivers/clk/clk-wm831x.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)