linux-kernel - Re: [PATCH 1/2] rtc: omap: Fix selecting external osc

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Date:   Sat, 5 Nov 2016 03:35:41 +0100
From:   Alexandre Belloni <alexandre.belloni@...e-electrons.com>
To:     Keerthy <j-keerthy@...com>
Cc:     a.zummo@...ertech.it, rtc-linux@...glegroups.com,
        linux-omap@...r.kernel.org, linux-kernel@...r.kernel.org,
        lokeshvutla@...com, t-kristo@...com
Subject: Re: [PATCH 1/2] rtc: omap: Fix selecting external osc

On 27/10/2016 at 11:27:25 +0530, Keerthy wrote :
> From: Lokesh Vutla <lokeshvutla@...com>
> 
> 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: 399cf0f63f6f2 ("rtc: omap: Add external clock enabling support")
> Signed-off-by: Keerthy <j-keerthy@...com>
> Signed-off-by: Lokesh Vutla <lokeshvutla@...com>
> Signed-off-by: Dave Gerlach <d-gerlach@...com>
> ---
> 
> Boot tested and checked for rtc ticking on am335x-boneblack, am335x-bone
> am437x-gp-evm, dra7-evm, dra72-evm.
> 
>  drivers/rtc/rtc-omap.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
Both applied, thanks.

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