Messages in this thread | | | From | Martin Blumenstingl <> | Date | Fri, 29 Mar 2019 20:39:59 +0100 | Subject | Re: [PATCH 1/3] clk: meson: mpll: properly handle spread spectrum |
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Hi Jerome,
On Fri, Mar 29, 2019 at 4:34 PM Jerome Brunet <jbrunet@baylibre.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@baylibre.com> > --- > drivers/clk/meson/clk-mpll.c | 9 ++++++--- > drivers/clk/meson/clk-mpll.h | 1 + > 2 files changed, 7 insertions(+), 3 deletions(-) > > diff --git a/drivers/clk/meson/clk-mpll.c b/drivers/clk/meson/clk-mpll.c > index 64d31c8ba3d0..2d39a8bc367c 100644 > --- a/drivers/clk/meson/clk-mpll.c > +++ b/drivers/clk/meson/clk-mpll.c > @@ -141,9 +141,12 @@ static void mpll_init(struct clk_hw *hw) > /* Enable the fractional part */ > meson_parm_write(clk->map, &mpll->sdm_en, 1); > > - /* Set additional fractional part enable if required */ > - if (MESON_PARM_APPLICABLE(&mpll->ssen)) > - meson_parm_write(clk->map, &mpll->ssen, 1); > + /* Set spread spectrum if possible */ > + if (MESON_PARM_APPLICABLE(&mpll->ssen)) { > + unsigned int ss = > + mpll->flags & CLK_MESON_MPLL_SPREAD_SPECTRUM ? 1 : 0; > + meson_parm_write(clk->map, &mpll->ssen, ss); > + } this changes the "ssen" flag on all supported clocks from 1 (before this patch) to 0 (after this patch). is this on purpose and how does it affect existing clocks?
based on the original commit 1f737ffa13ef ("clk: meson: mpll: fix mpll0 fractional part ignored") it seems that CLK_MESON_MPLL_SPREAD_SPECTRUM should be set for mpll0 (at least on GXBB and Meson8b)
Martin
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