linux-kernel - Re: [PATCH v10 3/4] pwm: add microchip soft ip corePWM driver

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Date:   Fri, 30 Sep 2022 11:13:16 +0200
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Conor Dooley <conor.dooley@...rochip.com>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Daire McNamara <daire.mcnamara@...rochip.com>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-pwm@...r.kernel.org, linux-riscv@...ts.infradead.org
Subject: Re: [PATCH v10 3/4] pwm: add microchip soft ip corePWM driver

On Mon, Sep 19, 2022 at 03:29:19PM +0100, Conor Dooley wrote:
> Hey Uwe,
> 
> On Mon, Sep 19, 2022 at 03:50:08PM +0200, Uwe Kleine-König wrote:
> > On Mon, Sep 19, 2022 at 01:53:56PM +0100, Conor Dooley wrote:
> > > Because I was running into conflicts between the reporting here and some
> > > of the checks that I have added to prevent the PWM being put into an
> > > invalid state. On boot both negedge and posedge will be zero & this was
> > > preventing me from setting the period at all.
> > 
> > I don't understood that.
> 
> On startup, (negedge == posedge) is true as both are zero, but the reset
> values for prescale and period are actually 0x8. If on reset I try to
> set a small period, say "echo 1000 > period" apply() returns -EINVAL
> because of a check in the pwm core in pwm_apply_state() as I am
> attempting to set the period to lower than the out-of-reset duty cycle.

You're supposed to keep the period for pwm#1 untouched while configuring
pwm#0 only if pwm#1 already has a consumer. So if pwm#1 isn't requested,
you can change the period for pwm#0.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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