From: Neil Armstrong <narmstrong@baylibre.com> To: David Rivshin <drivshin@awxrd.com> Cc: "Matthijs van Duin" <matthijsvanduin@gmail.com>, "H. Nikolaus Schaller" <hns@goldelico.com>, "Benoît Cousson" <bcousson@baylibre.com>, "Tony Lindgren" <tony@atomide.com>, "Rob Herring" <robh+dt@kernel.org>, "Mark Rutland" <mark.rutland@arm.com>, "Russell King" <linux@armlinux.org.uk>, marek@goldelico.com, linux-omap@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, letux-kernel@openphoenux.org Subject: Re: [PATCH] ARM: dts: omap3-gta04: reduce panel backlight PWM frequency to 83Hz Date: Mon, 12 Sep 2016 17:03:32 +0200 [thread overview] Message-ID: <a7975f8d-e2e2-6554-4bab-af8c00dc9252@baylibre.com> (raw) In-Reply-To: <20160912104155.267876a2.drivshin@awxrd.com> On 09/12/2016 04:41 PM, David Rivshin wrote: > On Sat, 10 Sep 2016 15:48:28 +0200 > Neil Armstrong <narmstrong@baylibre.com> wrote: > >> Le 10/09/2016 05:17, Matthijs van Duin a écrit : >>> On Mon, Sep 05, 2016 at 11:16:38AM +0200, H. Nikolaus Schaller wrote: >>>> This helps to get 100% intensity closer to "always on". [...] >>> } >>> >>> At the time I used a scope to check the exact behaviour of dmtimer pwm >>> on a dm814x. My notes mention (when pwm enabled): >>> match < reload output on continuous >>> match == reload output on 1 cycle, off period-1 cycles >>> match == -2 output on period-1 cycles, off 1 cycle >>> match == -1 output freezes >>> >>> Hope this helps >> >> Hi, >> >> I think these corner cases should definitely be handled in the dmtimer driver. > > Do you mean to modify the dmtimer driver itself, or the pwm-omap-dmtimer > driver? > > IIRC from the last time I was in the pwm-omap-dmtimer driver, it seemed to > me that the 0% and 100% cases could/should be handled as simple special > cases there. I think the dmtimer driver itself has the necessary API to the > HW, but I'd need to re-familiarize myself with it to remember the details > of what I was thinking. > > Actually, I did mention some thoughts on this a previous thread where > Adam Ford was using pwm-omap-dmtimer for a backlight: > http://www.spinics.net/lists/linux-omap/msg126006.html > So it may be as simple as using PWM_OMAP_DMTIMER_TRIGGER_NONE and passing > def_on according to whether 0 or 100% duty were requested (and polarity). Yes it's exactly what I was talking about. > > >> >> I'll try to post a fix to handle these, thanks for the original code dump. >> >>> >>> Matthijs >>> >> >> Neil Thanks, Neil
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From: Neil Armstrong <narmstrong-rdvid1DuHRBWk0Htik3J/w@public.gmane.org> To: David Rivshin <drivshin-WHIoityCHfoAvxtiuMwx3w@public.gmane.org> Cc: "Matthijs van Duin" <matthijsvanduin-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, "H. Nikolaus Schaller" <hns-xXXSsgcRVICgSpxsJD1C4w@public.gmane.org>, "Benoît Cousson" <bcousson-rdvid1DuHRBWk0Htik3J/w@public.gmane.org>, "Tony Lindgren" <tony-4v6yS6AI5VpBDgjK7y7TUQ@public.gmane.org>, "Rob Herring" <robh+dt-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, "Mark Rutland" <mark.rutland-5wv7dgnIgG8@public.gmane.org>, "Russell King" <linux-I+IVW8TIWO2tmTQ+vhA3Yw@public.gmane.org>, marek-xXXSsgcRVICgSpxsJD1C4w@public.gmane.org, linux-omap-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, letux-kernel-S0jZdbWzriLCfDggNXIi3w@public.gmane.org Subject: Re: [PATCH] ARM: dts: omap3-gta04: reduce panel backlight PWM frequency to 83Hz Date: Mon, 12 Sep 2016 17:03:32 +0200 [thread overview] Message-ID: <a7975f8d-e2e2-6554-4bab-af8c00dc9252@baylibre.com> (raw) In-Reply-To: <20160912104155.267876a2.drivshin-WHIoityCHfoAvxtiuMwx3w@public.gmane.org> On 09/12/2016 04:41 PM, David Rivshin wrote: > On Sat, 10 Sep 2016 15:48:28 +0200 > Neil Armstrong <narmstrong-rdvid1DuHRBWk0Htik3J/w@public.gmane.org> wrote: > >> Le 10/09/2016 05:17, Matthijs van Duin a écrit : >>> On Mon, Sep 05, 2016 at 11:16:38AM +0200, H. Nikolaus Schaller wrote: >>>> This helps to get 100% intensity closer to "always on". [...] >>> } >>> >>> At the time I used a scope to check the exact behaviour of dmtimer pwm >>> on a dm814x. My notes mention (when pwm enabled): >>> match < reload output on continuous >>> match == reload output on 1 cycle, off period-1 cycles >>> match == -2 output on period-1 cycles, off 1 cycle >>> match == -1 output freezes >>> >>> Hope this helps >> >> Hi, >> >> I think these corner cases should definitely be handled in the dmtimer driver. > > Do you mean to modify the dmtimer driver itself, or the pwm-omap-dmtimer > driver? > > IIRC from the last time I was in the pwm-omap-dmtimer driver, it seemed to > me that the 0% and 100% cases could/should be handled as simple special > cases there. I think the dmtimer driver itself has the necessary API to the > HW, but I'd need to re-familiarize myself with it to remember the details > of what I was thinking. > > Actually, I did mention some thoughts on this a previous thread where > Adam Ford was using pwm-omap-dmtimer for a backlight: > http://www.spinics.net/lists/linux-omap/msg126006.html > So it may be as simple as using PWM_OMAP_DMTIMER_TRIGGER_NONE and passing > def_on according to whether 0 or 100% duty were requested (and polarity). Yes it's exactly what I was talking about. > > >> >> I'll try to post a fix to handle these, thanks for the original code dump. >> >>> >>> Matthijs >>> >> >> Neil Thanks, Neil -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html
next prev parent reply other threads:[~2016-09-12 15:03 UTC|newest] Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top 2016-09-05 9:16 [PATCH] ARM: dts: omap3-gta04: reduce panel backlight PWM frequency to 83Hz H. Nikolaus Schaller 2016-09-10 3:17 ` Matthijs van Duin 2016-09-10 7:08 ` H. Nikolaus Schaller 2016-09-10 7:14 ` [Letux-kernel] " H. Nikolaus Schaller 2016-09-10 7:14 ` H. Nikolaus Schaller 2016-09-10 8:20 ` Matthijs van Duin 2016-09-10 8:20 ` Matthijs van Duin 2016-09-10 9:10 ` H. Nikolaus Schaller 2016-09-13 22:07 ` Tony Lindgren 2016-09-13 22:07 ` Tony Lindgren 2016-09-14 4:28 ` H. Nikolaus Schaller 2016-09-14 4:28 ` H. Nikolaus Schaller 2016-09-14 18:12 ` Tony Lindgren 2016-09-14 18:12 ` Tony Lindgren 2016-09-10 13:48 ` Neil Armstrong 2016-09-10 13:48 ` Neil Armstrong 2016-09-12 14:41 ` David Rivshin 2016-09-12 15:03 ` Neil Armstrong [this message] 2016-09-12 15:03 ` Neil Armstrong
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