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Date: Fri, 16 Jul 2021 09:22:22 +0000 From: Billy Tsai <billy_tsai@...eedtech.com> To: Uwe Kleine-König <u.kleine-koenig@...gutronix.de> CC: "lee.jones@...aro.org" <lee.jones@...aro.org>, "robh+dt@...nel.org" <robh+dt@...nel.org>, "joel@....id.au" <joel@....id.au>, "andrew@...id.au" <andrew@...id.au>, "thierry.reding@...il.com" <thierry.reding@...il.com>, "p.zabel@...gutronix.de" <p.zabel@...gutronix.de>, "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>, "linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>, "linux-aspeed@...ts.ozlabs.org" <linux-aspeed@...ts.ozlabs.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "linux-pwm@...r.kernel.org" <linux-pwm@...r.kernel.org>, BMC-SW <BMC-SW@...eedtech.com> Subject: Re: [v9 2/2] pwm: Add Aspeed ast2600 PWM support Hello Uwe, On 2021/7/16, 3:10 PM, "Uwe Kleine-König" <u.kleine-koenig@...gutronix.de> wrote: Hello Billy, On Fri, Jul 16, 2021 at 01:48:20AM +0000, Billy Tsai wrote: >> On 2021/7/15, 11:06 PM, "Uwe Kleine-König" <u.kleine-koenig@...gutronix.de>> wrote: >> > Another is: The PWM doesn't support duty_cycle 0, on such a request the >> > PWM is disabled which results in a constant inactive level. >> >> > (This is correct, is it? Or does it yield a constant 0 level?) >> >> Our pwm can support duty_cycle 0 by unset CLK_ENABLE. > This has a slightly different semantic though. Some consumer might > expect that the following sequence: > pwm_apply(mypwm, { .period = 10000, .duty_cycle = 10000, .enabled = true }) > pwm_apply(mypwm, { .period = 10000, .duty_cycle = 0, .enabled = true }) > pwm_apply(mypwm, { .period = 10000, .duty_cycle = 10000, .enabled = true }) > results in the output being low for an integer multiple of 10 µs. This > isn't given with setting CLK_ENABLE to zero, is it? (I didn't recheck, > if the PWM doesn't complete periods on reconfiguration this doesn't > matter much though.) Thanks for the explanation. Our hardware actually can only support duty from 1/256 to 256/256. For this situation I can do possible solution: We can though change polarity to meet this requirement. Inverse the pin and use duty_cycle 100. But I think this is not a good solution for this problem right?
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