linux-kernel - Re: [rtc-linux] [PATCH] rtc: OMAP: Add external 32k clock feature

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Date:	Tue, 7 Apr 2015 08:59:41 +0530
From:	Keerthy <a0393675@...com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	<rtc-linux@...glegroups.com>
CC:	Keerthy <j-keerthy@...com>, <a.zummo@...ertech.it>,
	<linux-kernel@...r.kernel.org>, <linux-omap@...r.kernel.org>
Subject: Re: [rtc-linux] [PATCH] rtc: OMAP: Add external 32k clock feature

Hi Andrew,

Apologies for replying late.

On Wednesday 25 March 2015 04:29 AM, Andrew Morton wrote:
> On Tue, 3 Mar 2015 15:12:02 +0530 Keerthy <j-keerthy@...com> wrote:
>
>> Add external 32k clock feature. The internal clock will be gated during suspend.
>> Hence make use of the external 32k clock so that rtc is functional accross
>> suspend/resume.
>>
>> ...
>>
>> @@ -446,6 +449,7 @@ static const struct omap_rtc_device_type omap_rtc_default_type = {
>>
>>   static const struct omap_rtc_device_type omap_rtc_am3352_type = {
>>   	.has_32kclk_en	= true,
>> +	.has_osc_ext_32k = true,
>>   	.has_kicker	= true,
>>   	.has_irqwakeen	= true,
>>   	.has_pmic_mode	= true,
>> @@ -543,7 +547,16 @@ static int __init omap_rtc_probe(struct platform_device *pdev)
>>   	if (rtc->type->has_32kclk_en) {
>>   		reg = rtc_read(rtc, OMAP_RTC_OSC_REG);
>>   		rtc_writel(rtc, OMAP_RTC_OSC_REG,
>> -				reg | OMAP_RTC_OSC_32KCLK_EN);
>> +			   reg | OMAP_RTC_OSC_32KCLK_EN);
>> +	}
>> +
>> +	/* Enable External clock as the source */
>> +
>> +	if (rtc->type->has_osc_ext_32k) {
>> +		rtc_writel(rtc, OMAP_RTC_OSC_REG,
>> +			   (OMAP_RTC_OSC_EXT_32K |
>> +			   rtc_read(rtc, OMAP_RTC_OSC_REG)) &
>> +			   (~OMAP_RTC_OSC_OSC32K_GZ));
>>   	}
>
> How do we know that all systems have this external clock and that it
> works OK?
>

AM335 and AM43X have the external clock feature which we choose using 
RTC_OSC_REG. I verified it works OK by seeing the RTC seconds ticking 
even after switching the source to the external 32k Clock.

Regards,
Keerthy
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