From mboxrd@z Thu Jan 1 00:00:00 1970 From: Lothar =?UTF-8?B?V2HDn21hbm4=?= Subject: Re: [PATCH] ARM: dts: imx53: add support for Ka-Ro TX53 modules Date: Fri, 13 Dec 2013 14:10:01 +0100 Message-ID: <20131213141001.389a178e@ipc1.ka-ro> References: <1386852128-32220-1-git-send-email-LW@KARO-electronics.de> <20131213081744.GR18380@S2101-09.ap.freescale.net> <20131213105417.71a42133@ipc1.ka-ro> <20131213121646.GU18380@S2101-09.ap.freescale.net> <20131213134240.595d27ae@ipc1.ka-ro> <20131213125719.GM24559@pengutronix.de> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <20131213125719.GM24559-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org> Sender: devicetree-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Sascha Hauer Cc: Shawn Guo , linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Rob Herring , Pawel Moll , Mark Rutland , Ian Campbell , Kumar Gala List-Id: devicetree@vger.kernel.org Hi, Sascha Hauer wrote: > On Fri, Dec 13, 2013 at 01:42:40PM +0100, Lothar Wa=C3=9Fmann wrote: > > Hi, > >=20 > > Shawn Guo wrote: > > > On Fri, Dec 13, 2013 at 10:54:17AM +0100, Lothar Wa=C3=9Fmann wro= te: > > > > > > + compatible =3D "pwm-backlight"; > > > > > > + pwms =3D <&pwm2 0 500000>; > > > > > > + power-supply =3D <®_3v3>; > > > > > > + brightness-levels =3D < > > > > > > + 100 99 98 97 96 95 94 93 92 91 > > > > > > + 90 89 88 87 86 85 84 83 82 81 > > > > > > + 80 79 78 77 76 75 74 73 72 71 > > > > > > + 70 69 68 67 66 65 64 63 62 61 > > > > > > + 60 59 58 57 56 55 54 53 52 51 > > > > > > + 50 49 48 47 46 45 44 43 42 41 > > > > > > + 40 39 38 37 36 35 34 33 32 31 > > > > > > + 30 29 28 27 26 25 24 23 22 21 > > > > > > + 20 19 18 17 16 15 14 13 12 11 > > > > > > + 10 9 8 7 6 5 4 3 2 1 > > > > > > + 0 > > > > >=20 > > > > > Why is it so unique to start with 100 and end with 0? Does i= t even > > > > > work? Here is what I read from bindings doc. > > > > >=20 > > > > Yes, it works. The backlight control of the displays we typical= ly use > > > > is active low. This is a poor man's way to get an inverted PWM = output! > > > > (And one in which the number written to the sysfs file correspo= nds to > > > > the actual duty cycle of the PWM output) > > >=20 > > > I think Linux pwm driver should be improved for this case rather = than > > > manipulate device tree in a way that violate the defined bindings= =2E > > > > > I admit I would be happier with a 'polarity' flag like other PWM > > drivers provide it. I tried to add polarity support in the generic = PWM > > layer, so that all HW drivers that do not support inversion in HW c= an > > make use of it, but this gives problems with client drivers that do= n't > > know about the inversion and disable the PWM when the duty cycle is= set > > to 0. > > Maybe I'll find some time to find a proper solution for this issue. >=20 > Actually the i.MX supports inversion in hardware. It's bit 18 in the > PWMCR register. >=20 I totally missed this up to now. :( Is it true for all i.MX SoCs? Or do we need to distinguish between SoCs that can do the inversion and those that cannot? I could provide a patch to utilize this feature, but probably not before the new year. There is something called 'vacation' in the way. ;= ) Lothar Wa=C3=9Fmann --=20 ___________________________________________________________ Ka-Ro electronics GmbH | Pascalstra=C3=9Fe 22 | D - 52076 Aachen Phone: +49 2408 1402-0 | Fax: +49 2408 1402-10 Gesch=C3=A4ftsf=C3=BChrer: Matthias Kaussen Handelsregistereintrag: Amtsgericht Aachen, HRB 4996 www.karo-electronics.de | info-AvR2QvxeiV7DiMYJYoSAnRvVK+yQ3ZXh@public.gmane.org ___________________________________________________________ -- To unsubscribe from this list: send the line "unsubscribe devicetree" i= n the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html