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Received: from shell.armlinux.org.uk ([fd8f:7570:feb6:1:5054:ff:fe00:4ec]:45098) by pandora.armlinux.org.uk with esmtpsa (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1kwlm9-0000lV-Up; Tue, 05 Jan 2021 12:49:25 +0000 Received: from linux by shell.armlinux.org.uk with local (Exim 4.92) (envelope-from ) id 1kwlm2-0007jF-52; Tue, 05 Jan 2021 12:49:18 +0000 Date: Tue, 5 Jan 2021 12:49:18 +0000 From: Russell King - ARM Linux admin To: Baruch Siach Subject: Re: [PATCH v5 1/4] gpio: mvebu: fix pwm get_state period calculation Message-ID: <20210105124917.GC1551@shell.armlinux.org.uk> References: <0cd077886d37699bdf0a20295fd8ee422e5285b5.1609849176.git.baruch@tkos.co.il> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <0cd077886d37699bdf0a20295fd8ee422e5285b5.1609849176.git.baruch@tkos.co.il> User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210105_075246_214998_AB8D034E X-CRM114-Status: GOOD ( 19.02 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Andrew Lunn , Sascha Hauer , linux-pwm@vger.kernel.org, Linus Walleij , Chris Packham , linux-gpio@vger.kernel.org, Rob Herring , Bartosz Golaszewski , devicetree@vger.kernel.org, Thierry Reding , Thomas Petazzoni , Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= , Ralph Sennhauser , Lee Jones , Gregory Clement , linux-arm-kernel@lists.infradead.org, Sebastian Hesselbarth Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, Jan 05, 2021 at 02:42:28PM +0200, Baruch Siach wrote: > The period is the sum of on and off values. > > Reported-by: Russell King > Fixes: 757642f9a584e ("gpio: mvebu: Add limited PWM support") > Signed-off-by: Baruch Siach > --- > drivers/gpio/gpio-mvebu.c | 16 ++++++---------- > 1 file changed, 6 insertions(+), 10 deletions(-) > > diff --git a/drivers/gpio/gpio-mvebu.c b/drivers/gpio/gpio-mvebu.c > index 672681a976f5..ac7cb6d3702e 100644 > --- a/drivers/gpio/gpio-mvebu.c > +++ b/drivers/gpio/gpio-mvebu.c > @@ -679,17 +679,13 @@ static void mvebu_pwm_get_state(struct pwm_chip *chip, > regmap_read(mvpwm->regs, mvebu_pwmreg_blink_off_duration(mvpwm), &u); > val = (unsigned long long) u * NSEC_PER_SEC; > do_div(val, mvpwm->clk_rate); > - if (val < state->duty_cycle) { > + val += state->duty_cycle; > + if (val > UINT_MAX) > + state->period = UINT_MAX; > + else if (val) > + state->period = val; > + else > state->period = 1; Are you sure this is the correct solution? Aren't you introducing rounding errors? The hardware will count to (on + off) clock ticks, so the right way to convert that is to add the two together and then convert to nanoseconds, which may result in a single rounding error. If you convert each individually to nanoseconds, then you can end up with two sets of rounding errors. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last! _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel