On Fri, Mar 4, 2016 at 2:01 PM, David Rivshin (Allworx) <drivshin.allworx@xxxxxxxxx> wrote: > On Fri, 4 Mar 2016 10:29:07 -0600 > Adam Ford <aford173@xxxxxxxxx> wrote: > >> I am OK with it. 0% vs 1% is not perceivable and neither is 99% vs 100%. > > IIRC, you tested with none of these patches, and with all of them. You > might want to double check the behavior with just patch 1 and 3, since > that's what Thierry applied. I'm just concerned that the behavior now > might be worse at one extreme or the other, compared to your previous > tests. > I will give them a try this afternoon and see how they are perceived. I am offsite, so I don't have an oscilloscope to actually observe the waveform. adam >> >> Thanks! >> >> Adam >> On Mar 4, 2016 10:27 AM, "David Rivshin (Allworx)" < >> drivshin.allworx@xxxxxxxxx> 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? >> > >> > 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. >> > >> > > -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
