| Message ID | 20190513123115.18145-2-jbrunet@baylibre.com (mailing list archive) |
|---|---|
| State | Not Applicable |
| Delegated to: | Neil Armstrong |
| Headers | show |
| Series | clk: meson: fix mpll jitter | expand |
On Mon, May 13, 2019 at 2:31 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> 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@googlemail.com> [0] https://patchwork.kernel.org/patch/10877431/
diff --git a/drivers/clk/meson/clk-mpll.c b/drivers/clk/meson/clk-mpll.c index f76850d99e59..d3f42e086431 100644 --- 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 cf79340006dd..0f948430fed4 100644 --- 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;
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(-)