On Fri, Mar 04, 2016 at 11:27:36AM -0500, David Rivshin (Allworx) wrote: > On Fri, 4 Mar 2016 16:19:48 +0100 > Thierry Reding <thierry.reding@xxxxxxxxx> wrote: > > > On Fri, Feb 26, 2016 at 08:31:00PM -0500, David Rivshin (Allworx) wrote: > > > On Fri, 29 Jan 2016 23:26:50 -0500 > > > "David Rivshin (Allworx)" <drivshin.allworx@xxxxxxxxx> wrote: > > > > > > > From: David Rivshin <drivshin@xxxxxxxxxxx> > > > > > > > > When using a short PWM period (approaching the min of 2/clk_rate), > > > > pwm-omap-dmtimer does not produce accurate results. In the worst case a > > > > requested period of 2/clk_rate would result in a real period of 4/clk_rate > > > > instead. This is a series includes a fix for that problem, as well as > > > > other related improvements, and is based on the current linux-pwm/for-next > > > > tip. > > > > > > > > I have tested on a Sitara AM335x platform, using a scope to verify the > > > > output with a variety of periods and duty cycles. This includes a PWM > > > > rate up clk_rate/2 with 50% duty cycle (e.g. generating fclk/2) with > > > > both 32768Hz and 24MHz fclks. I do not have an OMAP4 board to test with, > > > > although appropriate sections in the the reference manuals appear > > > > substantially the same, so I believe the changes are equally correct > > > > there. > > > > > > > > Note that the OMAP4 TRMs do effectively state that the maximum PWM > > > > rate is clk_rate/4, so at very fast PWM rates the behavior may not be > > > > as reliable as I observed with Sitara. Although I suspect that it's > > > > the same module and will also work, at least under some circumstances. > > > > If anyone with OMAP4 hardware and a scope is so inclined, I would be > > > > curious to know the results. > > > > > > > > David Rivshin (4): > > > > pwm: omap-dmtimer: fix inaccurate period/duty_cycle calculation > > > > pwm: omap-dmtimer: add sanity checking for load and match values > > > > pwm: omap-dmtimer: round load and match values rather than truncate > > > > pwm: omap-dmtimer: add dev_dbg() message for effective period and duty > > > > cycle > > > > > > > > drivers/pwm/pwm-omap-dmtimer.c | 71 ++++++++++++++++++++++++++++++++---------- > > > > 1 file changed, 55 insertions(+), 16 deletions(-) > > > > > > > > > > Hi Thierry, > > > > > > Gentle ping. It does not look like you've taken this series, and I > > > wanted to make sure you're not waiting on something from me. It would > > > be nice to get at least the first patch into 4.5, if possible. > > > > I've applied patches 1 and 3, and I'm planning on sending out a pull > > request for inclusion in v4.5-rc7 later on. > > Thanks! > > > Patches 2 and 4 didn't seem ready/critical, so let's finish those up > > for v4.6-rc1. > > I know there was a lot of discussion on 4, but I'm not sure what the > concern is on patch 2. Is there something specific you're thinking of? Patch 2 sounded like some optional sanity checking which we didn't hit anyway in the current code. Hence I didn't consider it a fix. > FYI, I know that Adam Ford is using this driver as the backend for > a pwm-backlight control. Without patch 2 this driver will not configure > the HW in a legal way at 0 or 100% duty cycle. However, I forget what > the practical effect of that is, and Adam seemed to indicate it was OK > for his purposes. Okay, I'll hold back a little longer to give you some time to test. Thierry
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