Commit 3984903a authored Oct 27, 2016 by Lokesh Vutla Committed by Alexandre Belloni Nov 04, 2016

rtc: omap: Fix selecting external osc



RTC can be clocked from an external 32KHz oscillator, or from the
Peripheral PLL. The RTC has an internal oscillator buffer to support
direct operation with a crystal.

            ----------------------------------------
            |       Device          ---------       |
            |                       |       |       |
            |                       | RTCSS |       |
            |       ---------       |       |       |
    OSC     |<------| RTC   |       |       |       |
            |------>| OSC   |---    |       |       |
            |       --------   |    |       |       |
            |                   ----|clk    |       |
            |       --------   |    |       |       |
            |       | PRCM  |---    |       |       |
            |       --------        --------        |
            ----------------------------------------

The RTC functional clock is sourced by default from the clock derived
from the Peripheral PLL. In order to select source as external osc clk
the following changes needs to be done:
- Enable the RTC OSC (RTC_OSC_REG[4]OSC32K_GZ = 0)
- Enable the clock mux(RTC_OSC_REG[6]K32CLK_EN = 1)
- Select the external clock source (RTC_OSC_REG[3]32KCLK_SEL = 1)

Fixes: 399cf0f6 ("rtc: omap: Add external clock enabling support")
Signed-off-by: Keerthy <j-keerthy@ti.com>
Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
Signed-off-by: Dave Gerlach <d-gerlach@ti.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>

parent 368e21ae

drivers/rtc/rtc-omap.c

+4 −2

Original line number	Diff line number	Diff line
		@@ -113,6 +113,7 @@
		/* OMAP_RTC_OSC_REG bit fields: */
		#define OMAP_RTC_OSC_32KCLK_EN BIT(6)
		#define OMAP_RTC_OSC_SEL_32KCLK_SRC BIT(3)
		#define OMAP_RTC_OSC_OSC32K_GZ_DISABLE BIT(4)

		/* OMAP_RTC_IRQWAKEEN bit fields: */
		#define OMAP_RTC_IRQWAKEEN_ALARM_WAKEEN BIT(1)
		@@ -786,8 +787,9 @@ static int omap_rtc_probe(struct platform_device *pdev)
		*/
		if (rtc->has_ext_clk) {
		reg = rtc_read(rtc, OMAP_RTC_OSC_REG);
		rtc_write(rtc, OMAP_RTC_OSC_REG,
		reg \| OMAP_RTC_OSC_SEL_32KCLK_SRC);
		reg &= ~OMAP_RTC_OSC_OSC32K_GZ_DISABLE;
		reg \|= OMAP_RTC_OSC_32KCLK_EN \| OMAP_RTC_OSC_SEL_32KCLK_SRC;
		rtc_writel(rtc, OMAP_RTC_OSC_REG, reg);
		}

		rtc->type->lock(rtc);

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