linux-kernel - Re: [PATCH 03/14] ASoC: sun4i-i2s: Add apb reset

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Date:   Tue, 4 Oct 2016 17:42:18 +0200
From:   Maxime Ripard <maxime.ripard@...e-electrons.com>
To:     Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
Cc:     Mylène Josserand 
        <mylene.josserand@...e-electrons.com>, mark.rutland@....com,
        devicetree@...r.kernel.org, alsa-devel@...a-project.org,
        linux-sunxi@...glegroups.com, vinod.koul@...el.com,
        linux-kernel@...r.kernel.org, mturquette@...libre.com,
        tiwai@...e.com, sboyd@...eaurora.org, lgirdwood@...il.com,
        robh+dt@...nel.org, perex@...ex.cz, wens@...e.org,
        broonie@...nel.org, alexandre.belloni@...e-electrons.com,
        dmaengine@...r.kernel.org, lee.jones@...aro.org,
        linux-clk@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 03/14] ASoC: sun4i-i2s: Add apb reset

Hi,

On Tue, Oct 04, 2016 at 02:15:16PM +0200, Thomas Petazzoni wrote:
> Hello,
> 
> On Tue,  4 Oct 2016 11:46:16 +0200, Mylène Josserand wrote:
> 
> >  #include <sound/dmaengine_pcm.h>
> >  #include <sound/pcm_params.h>
> > @@ -589,6 +590,7 @@ static int sun4i_i2s_probe(struct platform_device *pdev)
> >  {
> >  	struct sun4i_i2s *i2s;
> >  	struct resource *res;
> > +	struct reset_control *reset_apb;
> >  	void __iomem *regs;
> >  	int irq, ret;
> >  
> > @@ -626,7 +628,19 @@ static int sun4i_i2s_probe(struct platform_device *pdev)
> >  		dev_err(&pdev->dev, "Can't get our mod clock\n");
> >  		return PTR_ERR(i2s->mod_clk);
> >  	}
> > -	
> > +
> > +	reset_apb = devm_reset_control_get(&pdev->dev, "apb_reset");
> 
> I believe this is a change in the Device Tree binding, since you're
> adding support for a new resource. Perhaps the Device Tree binding
> documentation should be updated accordingly?

Indeed.

You have two solutions to do that:
  - Either mark it as optional and use reset_control_get_optional
    (because here, you broke the other SoCs that have that controller
    but no reset line)
  - Or introduce a new compatible, and make the reset property
    mandatory for that new compatible.

I prefer the latter, since you get a stricter error check, and you
cannot end up in a situation where your driver probes but is
useless. But you'll find both in our drivers.

> > +	}
> > +
> > +	ret = reset_control_deassert(reset_apb);
> > +	if (ret < 0) {
> > +		dev_err(&pdev->dev, "Can't deassert apb reset (%d)\n", ret);
> > +		return ret;
> > +	}
> 
> Do you need to re-assert the reset line in the ->remove() hook?

Even better, you can add it to the runtime_pm hooks! :)

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

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