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From: Geert Uytterhoeven <>
To: Simon Horman <>
Cc: Geert Uytterhoeven <>,
	Magnus Damm <>,
	Linux-Renesas <>,
	linux-clk <>,
	Fabrizio Castro <>,
	Biju Das <>,
	Andrew Morton <>,
	Linux Kernel Mailing List <>
Subject: Re: [PATCH v4 3/5] clk: renesas: rcar-gen3: Support Z and Z2 clocks with high frequency parents
Date: Thu, 7 Feb 2019 16:05:58 +0100
Message-ID: <> (raw)
In-Reply-To: <>

Hi Simon,

On Thu, Feb 7, 2019 at 2:36 PM Simon Horman <> wrote:
> Support Z and Z2 clocks with parent frequencies greater than UINT32_MAX Hz
> (~4.29GHz).
> The DIV_ROUND_CLOSEST_ULL() macro accepts a 64bit dividend and 32bit
> divisor. This leads to truncation of the dividend, which is the Z or Z2

truncation of the divisor.

> parent clock frequency in HZ, on platforms where frequency of that clock is
> greater than UINT32_MAX Hz.
> To resolve this problem the DIV64_U64_ROUND_CLOSEST() macro, which an

which takes an

> unsigned 32bit dividend and divisor, is introduced.


> An earlier version of this patch made use of the existing
> DIV_ROUND_CLOSEST() macro, which accepts the prevailing type of the
> dividend and divisor. However, this does not compile on 32bit systems, such
> as i386 and mips, when called with the types used at this callsite, an
> unsigned long long dividend and unsigned long divisor.

Thanks for fixing this!

> This work is in preparation for supporting the Z2 cloco on the R-Car Gen3
> E3 (r8a77990) SoC which has a 4.8GHz parent clock.
> Signed-off-by: Simon Horman <>

With the above fixed:
Reviewed-by: Geert Uytterhoeven <>

> ---
> v4: Add and use DIV64_U64_ROUND_CLOSEST
> v2: New patch
> ---
>  drivers/clk/renesas/rcar-gen3-cpg.c |  4 ++--
>  include/linux/math64.h              | 13 +++++++++++++

While I have no issue taking this change through the clk-renesas tree if
Andrew provides his Acked-by, I think the introduction of
DIV64_U64_ROUND_CLOSEST() should be a separate patch.

However, given commit 68600f623d69da42 ("mm: don't miss the last page
because of round-off error") added both DIV64_U64_ROUND_UP() and its
user under mm/, there's precedence for not splitting it off...



Geert Uytterhoeven -- There's lots of Linux beyond ia32 --

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

  reply index

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-02-07 13:35 [PATCH v4 0/5] clk: renesas: r8a77990, r8a774c0: Add Z2 clock Simon Horman
2019-02-07 13:35 ` [PATCH v4 1/5] clk: renesas: rcar-gen3: Parameterise Z and Z2 clock fixed divisor Simon Horman
2019-02-07 13:35 ` [PATCH v4 2/5] clk: renesas: rcar-gen3: Parameterise Z and Z2 clock offset Simon Horman
2019-02-07 13:35 ` [PATCH v4 3/5] clk: renesas: rcar-gen3: Support Z and Z2 clocks with high frequency parents Simon Horman
2019-02-07 15:05   ` Geert Uytterhoeven [this message]
2019-02-07 15:22     ` Simon Horman
2019-02-07 13:35 ` [PATCH v4 4/5] clk: renesas: r8a77990: Add Z2 clock Simon Horman
2019-02-07 13:35 ` [PATCH v4 5/5] clk: renesas: r8a774c0: " Simon Horman

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