linux-kernel - Re: [PATCH V4] PWM: Add SPEAr PWM chip driver support

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Message-ID: <20121024054333.GB9787@avionic-0098.mockup.avionic-design.de>
Date:	Wed, 24 Oct 2012 07:43:34 +0200
From:	Thierry Reding <thierry.reding@...onic-design.de>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	Shiraz Hashim <shiraz.hashim@...com>, linux-kernel@...r.kernel.org,
	spear-devel@...t.st.com
Subject: Re: [PATCH V4] PWM: Add SPEAr PWM chip driver support

On Mon, Oct 22, 2012 at 07:25:45PM +0530, Viresh Kumar wrote:
> On 22 October 2012 16:36, Shiraz Hashim <shiraz.hashim@...com> wrote:
> > Add support for PWM chips present on SPEAr platforms. These PWM
> > chips support 4 channel output with programmable duty cycle and
> > frequency.
> >
> > More details on these PWM chips can be obtained from relevant
> > chapter of reference manual, present at following[1] location.
> >
> > 1. http://www.st.com/internet/mcu/product/251211.jsp
> >
> > Cc: Thierry Reding <thierry.reding@...onic-design.de>
> > Signed-off-by: Shiraz Hashim <shiraz.hashim@...com>
> > Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
> > Reviewed-by: Vipin Kumar <vipin.kumar@...com>
> 
> Acked-by: Viresh Kumar <viresh.kumar@...aro.org>
> 
> > diff --git a/drivers/pwm/pwm-spear.c b/drivers/pwm/pwm-spear.c
> > +static int spear_pwm_probe(struct platform_device *pdev)
> > +{
> 
> > +       ret = pwmchip_add(&pc->chip);
> > +       if (ret < 0) {
> > +               dev_err(&pdev->dev, "pwmchip_add() failed: %d\n", ret);
> > +               return ret;
> > +       }
> 
> Sorry couldn't think of this complex situation earlier :(
> 
> Can it happen that we get a request for a pwm here and its config or enable
> gets called...?
> 
> If yes, then we must call clk_prepare() before doing pwmchip_add?? Otherwise
> you will see a crash :)
> 
> @Thierry: Can this happen?

Yeah, it's very unlikely to happen, but it could. See my reply to the
patch.

Thierry

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