linux-kernel - Re: [PATCH 2/2] pwm: pca9685: fix prescaler initialization

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Date:   Thu, 19 Jan 2017 17:52:10 +0100
From:   Clemens Gruber <clemens.gruber@...ruber.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Thierry Reding <thierry.reding@...il.com>
Cc:     linux-pwm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Florian Vaussard <florian.vaussard@...g-vd.ch>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>
Subject: Re: [PATCH 2/2] pwm: pca9685: fix prescaler initialization

On Thu, Jan 19, 2017 at 06:10:08PM +0200, Andy Shevchenko wrote:
> Combining with your proposal I would see the best approach is to set
> pca->period_ns accordingly to current prescaler value if you want to.

Yes, I agree.

> In your patch I see no benefit, since it's quite unlikely user will want
> to have 5ms period among all possibilities.

It is the hardware default, but you are right, the user probably does
not care about that.

> So, summarize, I prefer (in order of preference from high to low):
> - enforce default prescaler value based on default period (it's just one
> line to write a register)
> - calculate default period based on actual prescaler value

Let's go with this one. I'll spin up a v2 where I calculate the
period_ns value from the current prescaler value in the probe function.

--

Thierry: I think you could merge v1 of patch 1/2 from my series
independently.

I'll send v2 of patch 2/2 with aforementioned changes in the next days.

Thanks,
Clemens