clk: meson: mpll: properly handle spread spectrum

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")
Tested-by: Martin Blumenstingl<martin.blumenstingl@googlemail.com>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>

diff --git a/drivers/clk/meson/clk-mpll.c b/drivers/clk/meson/clk-mpll.c
index f76850d99e591b1fb817665519863986356c736c..d3f42e0864313966a0e2b5cad6695d3b3e71984a 100644 (file)
--- a/drivers/clk/meson/clk-mpll.c
+++ b/drivers/clk/meson/clk-mpll.c
@@ -119,9 +119,12 @@ static int mpll_set_rate(struct clk_hw *hw,
        meson_parm_write(clk->map, &mpll->sdm, sdm);
        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);
+       }
 
        /* Set the integer divider part */
        meson_parm_write(clk->map, &mpll->n2, n2);

diff --git a/drivers/clk/meson/clk-mpll.h b/drivers/clk/meson/clk-mpll.h
index cf79340006dd765932690c17f47ef93a27af9a0b..0f948430fed4852b2d4e7657d4ac307bc2755420 100644 (file)
--- a/drivers/clk/meson/clk-mpll.h
+++ b/drivers/clk/meson/clk-mpll.h
@@ -23,6 +23,7 @@ struct meson_clk_mpll_data {
 };
 
 #define CLK_MESON_MPLL_ROUND_CLOSEST   BIT(0)
+#define CLK_MESON_MPLL_SPREAD_SPECTRUM BIT(1)
 
 extern const struct clk_ops meson_clk_mpll_ro_ops;
 extern const struct clk_ops meson_clk_mpll_ops;