linux-kernel - Re: [PATCH v2 1/7] clk: meson: mpll: properly handle spread spectrum

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Message-ID: <CAFBinCBOtsSCg40L+PovAwN2dvLpDO7KMhJpcftpSiv+moBDSA@mail.gmail.com>
Date:   Tue, 14 May 2019 20:16:28 +0200
From:   Martin Blumenstingl <martin.blumenstingl@...glemail.com>
To:     Jerome Brunet <jbrunet@...libre.com>
Cc:     Neil Armstrong <narmstrong@...libre.com>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Kevin Hilman <khilman@...libre.com>,
        linux-amlogic@...ts.infradead.org, linux-clk@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/7] clk: meson: mpll: properly handle spread spectrum

On Mon, May 13, 2019 at 2:31 PM Jerome Brunet <jbrunet@...libre.com> wrote:
>
> The bit 'SSEN' available on some MPLL DSS outputs is not related to the
> fractional part of the divider but to the function called
> 'Spread Spectrum'.
>
> This function might be used to solve EM issues by adding a jitter on
> clock signal. This widens the signal spectrum and weakens the peaks in it.
>
> While spread spectrum might be useful for some application, it is
> problematic for others, such as audio.
>
> This patch introduce a new flag to the MPLL driver to enable (or not) the
> spread spectrum function.
>
> Fixes: 1f737ffa13ef ("clk: meson: mpll: fix mpll0 fractional part ignored")
> Signed-off-by: Jerome Brunet <jbrunet@...libre.com>
in v1 [0] I checked that Ethernet is still working on my Odroid-C1.
I didn't repeat this test with v2 but since the logic has not changed
you can still add my:
Tested-by: Martin Blumenstingl<martin.blumenstingl@...glemail.com>


[0] https://patchwork.kernel.org/patch/10877431/