linux-kernel - Re: [PATCH 4/5] rtc: at91sam9: retain slow clock and check its rate

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Date:	Mon, 8 Sep 2014 21:22:18 +0200
From:	Boris BREZILLON <boris.brezillon@...e-electrons.com>
To:	Alexandre Belloni <alexandre.belloni@...e-electrons.com>
Cc:	Nicolas Ferre <nicolas.ferre@...el.com>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	Andrew Victor <linux@...im.org.za>,
	Alessandro Zummo <a.zummo@...ertech.it>,
	rtc-linux@...glegroups.com, Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>, devicetree@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/5] rtc: at91sam9: retain slow clock and check its rate

On Mon, 8 Sep 2014 19:33:38 +0200
Alexandre Belloni <alexandre.belloni@...e-electrons.com> wrote:

> On 03/09/2014 at 10:45:33 +0200, Boris Brezillon wrote :
> > The RTT block is using the slow clock and expect it to run at 32KHz.
> > Now that we moved to the CCF it's better to retain the clk reference so
> > that the CCF can't disable the slow clock considering it is unused.
> > 
> > Signed-off-by: Boris BREZILLON <boris.brezillon@...e-electrons.com>
> > ---
> >  drivers/rtc/rtc-at91sam9.c | 24 ++++++++++++++++++++++++
> >  1 file changed, 24 insertions(+)
> > 
> > diff --git a/drivers/rtc/rtc-at91sam9.c b/drivers/rtc/rtc-at91sam9.c
> > index 57014b7..5c5093b 100644
> > --- a/drivers/rtc/rtc-at91sam9.c
> > +++ b/drivers/rtc/rtc-at91sam9.c
> > @@ -21,6 +21,7 @@
> >  #include <linux/slab.h>
> >  #include <linux/platform_data/atmel.h>
> >  #include <linux/io.h>
> > +#include <linux/clk.h>
> >  
> >  /*
> >   * This driver uses two configurable hardware resources that live in the
> > @@ -74,6 +75,7 @@ struct sam9_rtc {
> >  	u32			imr;
> >  	void __iomem		*gpbr;
> >  	int 			irq;
> > +	struct clk		*sclk;
> >  };
> >  
> >  #define rtt_readl(rtc, field) \
> > @@ -373,6 +375,25 @@ static int at91_rtc_probe(struct platform_device *pdev)
> >  		return ret;
> >  	}
> >  
> > +	/* Retain slow clk if it is specified in the DT.
> > +	 * Do not complain if slow clk is missing, but check its rate
> > +	 * if it is available.
> > +	 */
> > +	rtc->sclk = devm_clk_get(&pdev->dev, NULL);
> > +	if (!IS_ERR(rtc->sclk)) {
> > +		if (clk_get_rate(rtc->sclk) != AT91_SLOW_CLOCK) {
> 
> I would not bother doing that check but use the value for MR instead of
> AT91_SLOW_CLOCK (see my previous mail).

Unfortunately, we can't get rid of this macro without modifying the
clk_lookup table in several arch/arm/mach-at91/<soc-name>.c files in
order to handle non DT/CCF cases (which will remain until all non DT
boards are moved to DT).
But I agree that this should be removed as soon as possible (AFAIR, all
SoCs have already been moved to the CCF).
How about adding a TODO comment ?

> 
> > +			dev_err(&pdev->dev,
> > +				"Invalid slow clock rate (expecting %lu got %lu)",
> > +				(unsigned long)AT91_SLOW_CLOCK,
> > +				clk_get_rate(rtc->sclk));
> > +			return -EINVAL;
> > +		}
> > +
> > +		ret = clk_prepare_enable(rtc->sclk);
> > +		if (ret)
> > +			return ret;
> > +	}
> > +
> >  	/* NOTE:  sam9260 rev A silicon has a ROM bug which resets the
> >  	 * RTT on at least some reboots.  If you have that chip, you must
> >  	 * initialize the time from some external source like a GPS, wall
> > @@ -397,6 +418,9 @@ static int at91_rtc_remove(struct platform_device *pdev)
> >  	/* disable all interrupts */
> >  	rtt_writel(rtc, MR, mr & ~(AT91_RTT_ALMIEN | AT91_RTT_RTTINCIEN));
> >  
> > +	if (!IS_ERR(rtc->sclk))
> > +		clk_disable_unprepare(rtc->sclk);
> > +
> >  	return 0;
> >  }
> >  
> > -- 
> > 1.9.1
> > 
> 



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