linux-kernel - Re: [PATCH] rtc: msm6242: Remove unneeded msm6242_set()/msm6242

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Message-ID: <20191118141909.GF3632@piout.net>
Date:   Mon, 18 Nov 2019 15:19:09 +0100
From:   Alexandre Belloni <alexandre.belloni@...tlin.com>
To:     Kars de Jong <jongk@...ux-m68k.org>
Cc:     Alessandro Zummo <a.zummo@...ertech.it>, linux-rtc@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Geert Uytterhoeven <geert@...ux-m68k.org>
Subject: Re: [PATCH] rtc: msm6242: Remove unneeded
 msm6242_set()/msm6242_clear() functions

On 16/11/2019 12:46:20+0100, Kars de Jong wrote:
> The msm6242_set()/msm6242_clear() functions are used when writing to Control
> Register D to set or clear the HOLD bit when reading the current time from
> the RTC.
> 
> Doing this with a read-modify-write cycle will potentially clear an
> interrupt condition which occurs between the read and the write.
> 
> The datasheet states the following about this:
> 
>   When writing the HOLD or 30 second adjust bits of register D, it is
>   necessary to write the IRQ FLAG bit to a "1".
> 
> Since the only other bits in the register are the 30 second adjust bit
> (which is not used) and the BUSY bit (which is read-only), the
> read-modify-write cycle can be replaced by a simple write with the IRQ FLAG
> bit set to 1 and the other bits (except HOLD) set to 0.
> 
> Cc: Geert Uytterhoeven <geert@...ux-m68k.org>
> Tested-by: Kars de Jong <jongk@...ux-m68k.org>
> Signed-off-by: Kars de Jong <jongk@...ux-m68k.org>
> ---
>  drivers/rtc/rtc-msm6242.c | 20 ++++----------------
>  1 file changed, 4 insertions(+), 16 deletions(-)
> 
Applied, thanks.

-- 
Alexandre Belloni, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com