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

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Date:	Tue, 9 Sep 2014 10:36:39 +0200
From:	Nicolas Ferre <nicolas.ferre@...el.com>
To:	Boris BREZILLON <boris.brezillon@...e-electrons.com>
CC:	Alexandre Belloni <alexandre.belloni@...e-electrons.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 08/09/2014 21:37, Boris BREZILLON :
> On Mon, 8 Sep 2014 21:22:18 +0200
> Boris BREZILLON <boris.brezillon@...e-electrons.com> wrote:
> 
>> 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).
> 
> After taking a closer look at what should be modified, I think it's
> worth it: there's only 5 impacted files (at91sam9260.c, at91sam9261.c,
> at91sam9263.c, at91sam9rl.c and at91sam9g45.c) and adding a clk_lookup
> entry is pretty easy.
> 
> Moreover we'll end up with a clean driver and won't have to bother
> about cleaning it up when dropping non DT boards support.

I vote for this => +1 ;-)

Bye,
-- 
Nicolas Ferre
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