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

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Date:   Mon, 18 Nov 2019 15:19:47 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Kars de Jong <jongk@...ux-m68k.org>
Cc:     Alessandro Zummo <a.zummo@...ertech.it>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        linux-rtc@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] rtc: msm6242: Remove unneeded msm6242_set()/msm6242_clear()
 functions

On Sat, Nov 16, 2019 at 12:46 PM Kars de Jong <jongk@...ux-m68k.org> 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>

Reviewed-by: Geert Uytterhoeven <geert@...ux-m68k.org>

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds