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Date: Tue, 8 Apr 2014 07:02:59 +0200 From: Lothar Waßmann <LW@...O-electronics.de> To: Thierry Reding <thierry.reding@...il.com> Cc: Sascha Hauer <s.hauer@...gutronix.de>, linux-kernel@...r.kernel.org, linux-pwm@...r.kernel.org, Shawn Guo <shawn.guo@...aro.org>, Sascha Hauer <kernel@...gutronix.de>, Arnd Bergmann <arnd@...db.de> Subject: Re: [PATCHv3 1/3] pwm: make the PWM_POLARITY flag in DTB optional Hi, Thierry Reding wrote: > On Wed, Apr 02, 2014 at 07:53:50AM +0200, Sascha Hauer wrote: > > On Fri, Mar 28, 2014 at 09:48:58AM +0100, Lothar Waßmann wrote: > [...] > > > @@ -183,8 +173,11 @@ static void of_pwmchip_add(struct pwm_chip *chip) > > > return; > > > > > > if (!chip->of_xlate) { > > > - chip->of_xlate = of_pwm_simple_xlate; > > > - chip->of_pwm_n_cells = 2; > > > + chip->of_xlate = of_pwm_xlate; > > > + if (chip->ops->set_polarity) > > > + chip->of_pwm_n_cells = 3; > > > + else > > > + chip->of_pwm_n_cells = 2; > > > > I think the presence of the set_polarity callback shouldn't influence > > the number of cells the parser expects. As commented on 2/2 this doesn't > > actually mean the device actually support polarity inversion. > > How so? A driver should only implement .set_polarity() if it supports > changing the polarity. > > That said, I agree that the presence of .set_polarity() shouldn't > determine the number of cells. You could have any number of other flags > set via the third cell. > > > Also, polarity inversion could still be done in software for hardware > > that doesn't support it. > > No. You cannot emulate polarity inversion in software. > Why not? duty_ns = period_ns - duty_ns; Lothar Waßmann -- ___________________________________________________________ Ka-Ro electronics GmbH | Pascalstraße 22 | D - 52076 Aachen Phone: +49 2408 1402-0 | Fax: +49 2408 1402-10 Geschäftsführer: Matthias Kaussen Handelsregistereintrag: Amtsgericht Aachen, HRB 4996 www.karo-electronics.de | info@...o-electronics.de ___________________________________________________________ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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