linux-kernel - Re: [PATCH RESEND] pwm: berlin: Don't use broken prescaler values

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Message-ID: <20180605091002.GB20649@ulmo>
Date:   Tue, 5 Jun 2018 11:10:02 +0200
From:   Thierry Reding <thierry.reding@...il.com>
To:     Thomas Hebb <tommyhebb@...il.com>
Cc:     linux-arm-kernel@...r.kernel.org,
        Antoine Tenart <antoine.tenart@...e-electrons.com>,
        sebastian.hesselbarth@...il.com, jszhang@...vell.com,
        "open list:PWM SUBSYSTEM" <linux-pwm@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RESEND] pwm: berlin: Don't use broken prescaler values

On Mon, Jun 04, 2018 at 02:32:41PM -0400, Thomas Hebb wrote:
> Six of the eight prescaler values available for Berlin PWM are not true
> prescalers but rather internal shifts that throw away the high bits of
> TCNT. Currently, we attempt to use those high bits, leading to erratic
> behavior. Restrict the prescaler configurations we select to only the
> two that respect the full range of TCNT.
> 
> Tested on BG2CD.
> 
> Signed-off-by: Thomas Hebb <tommyhebb@...il.com>
> ---
>  drivers/pwm/pwm-berlin.c | 45 ++++++++++++++++++++++------------------
>  1 file changed, 25 insertions(+), 20 deletions(-)

Antoine, Jisheng,

can you guys review this patch? I'm personally on the fence about this,
even if we can technically do the shift in software, I don't necessarily
see a reason why we can't "offload" to the hardware.

Thierry

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