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From: Geert Uytterhoeven <geert@linux-m68k.org>
To: Simon Horman <horms+renesas@verge.net.au>
Cc: Geert Uytterhoeven <geert+renesas@glider.be>,
	Magnus Damm <magnus.damm@gmail.com>,
	Linux-Renesas <linux-renesas-soc@vger.kernel.org>,
	linux-clk <linux-clk@vger.kernel.org>,
	Fabrizio Castro <fabrizio.castro@bp.renesas.com>,
	Biju Das <biju.das@bp.renesas.com>
Subject: Re: [PATCH v3 3/5] clk: renesas: rcar-gen3: Support Z and Z2 clocks with high frequency parents
Date: Tue, 5 Feb 2019 10:18:26 +0100
Message-ID: <CAMuHMdWX8j9W3wc5Xias+tK0ztQb89ngOw9uV2we2HMd__u_Xg@mail.gmail.com> (raw)
In-Reply-To: <20190131094021.3092-4-horms+renesas@verge.net.au>

On Thu, Jan 31, 2019 at 10:40 AM Simon Horman
<horms+renesas@verge.net.au> 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 numerator and 32bit
> denominator. This leads to truncation of the numerator, which is the Z or
> Z2 parent clock frequency in HZ, on platforms where frequency of that clock
> is greater than UINT32_MAX Hz.
>
> To resolve this problem the DIV_ROUND_CLOSEST() macro, which accepts the
> prevailing types of the numerator and denominator, is used. In this case
> the type of the numerator is unsigned long long (64 bit) and the type of
> the denominator is unsigned long (64bit on 64bit platforms and 32bit on
> 32bit platforms). This allows parents whose frequency is greater than
> UINT32_MAX Hz on 64bit platforms.
>
> This appears to be sufficient as this driver is only intended for use
> on 64bit systems. And in particular, the motivation for this change is
> to allow a 4.8GHz clock on the R-Car Gen3 E3 (r8a77990) SoC which is
> a 64bit platform.
>
> Signed-off-by: Simon Horman <horms+renesas@verge.net.au>

Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-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

  reply index

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-01-31  9:40 [PATCH v3 0/5] clk: renesas: r8a77990: Add Z2 clock Simon Horman
2019-01-31  9:40 ` [PATCH v3 1/5] clk: renesas: rcar-gen3: Parameterise Z and Z2 clock fixed divisor Simon Horman
2019-02-05  9:28   ` Geert Uytterhoeven
2019-01-31  9:40 ` [PATCH v3 2/5] clk: renesas: rcar-gen3: Parameterise Z and Z2 clock offset Simon Horman
2019-02-05  9:28   ` Geert Uytterhoeven
2019-02-05 10:48   ` Geert Uytterhoeven
2019-02-05 14:35     ` Simon Horman
2019-02-05 14:55       ` Geert Uytterhoeven
2019-02-05 15:14         ` Simon Horman
2019-01-31  9:40 ` [PATCH v3 3/5] clk: renesas: rcar-gen3: Support Z and Z2 clocks with high frequency parents Simon Horman
2019-02-05  9:18   ` Geert Uytterhoeven [this message]
2019-01-31  9:40 ` [PATCH v3 4/5] clk: renesas: r8a77990: Add Z2 clock Simon Horman
2019-02-05  9:27   ` Geert Uytterhoeven
2019-01-31  9:40 ` [PATCH/RFT v3 5/5] clk: renesas: r8a774c0: " Simon Horman
2019-01-31 11:01   ` Fabrizio Castro
2019-02-05  9:27   ` Geert Uytterhoeven
2019-02-05  9:30 ` [PATCH v3 0/5] clk: renesas: r8a77990: " Geert Uytterhoeven

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