[0/3] clk: meson: fix mpll jitter

Message

Jerome Brunet March 29, 2019, 3:33 p.m. UTC

As reported on this [0] mpll series, We are observing a lot of jitter
on the MPLL outputs of the g12a. No such jitter is seen on gx family.
On the axg family, only MPLL2 seems affected.

The jitter can be as high as +/- 4%.

This is a problem for audio application. This may cause distortion on
i2s and completely break SPDIF.

After exchanging with Amlogic, it seems he have activated (by mistake)
the 'spread spectrum' feature.

This patchset properly set the bit responsible for the spread spectrum
in the mpll driver and add the required correction in the related clock
controllers.

Jerome Brunet (3):
  clk: meson: mpll: properly handle spread spectrum
  clk: meson: gxbb: no spread spectrum on mpll0
  clk: meson: axg: spread spectrum is on mpll2

 drivers/clk/meson/axg.c      | 10 +++++-----
 drivers/clk/meson/clk-mpll.c |  9 ++++++---
 drivers/clk/meson/clk-mpll.h |  1 +
 drivers/clk/meson/gxbb.c     |  5 -----
 4 files changed, 12 insertions(+), 13 deletions(-)

Comments

Martin Blumenstingl March 30, 2019, 3:58 p.m. UTC | #1

On Fri, Mar 29, 2019 at 4:34 PM Jerome Brunet <[e-mail]> wrote:
>
> As reported on this [0] mpll series, We are observing a lot of jitter
> on the MPLL outputs of the g12a. No such jitter is seen on gx family.
> On the axg family, only MPLL2 seems affected.
>
> The jitter can be as high as +/- 4%.
>
> This is a problem for audio application. This may cause distortion on
> i2s and completely break SPDIF.
>
> After exchanging with Amlogic, it seems he have activated (by mistake)
> the 'spread spectrum' feature.
>
> This patchset properly set the bit responsible for the spread spectrum
> in the mpll driver and add the required correction in the related clock
> controllers.
>
> Jerome Brunet (3):
>   clk: meson: mpll: properly handle spread spectrum
this depends on a patch from your other series "clk: meson: fixup g12a
mpll": [0]
personally I would base the other series on this one because this one
contains a "Fixes" that (meaning that the patch will get backported
and that's easier if there aren't any conflicts)


Regards
Martin


[0] https://patchwork.kernel.org/patch/10868837/

Jerome Brunet April 1, 2019, 8:40 a.m. UTC | #2

On Sat, 2019-03-30 at 16:58 +0100, Martin Blumenstingl wrote:
> On Fri, Mar 29, 2019 at 4:34 PM Jerome Brunet <[e-mail]> wrote:
> > As reported on this [0] mpll series, We are observing a lot of jitter
> > on the MPLL outputs of the g12a. No such jitter is seen on gx family.
> > On the axg family, only MPLL2 seems affected.
> > 
> > The jitter can be as high as +/- 4%.
> > 
> > This is a problem for audio application. This may cause distortion on
> > i2s and completely break SPDIF.
> > 
> > After exchanging with Amlogic, it seems he have activated (by mistake)
> > the 'spread spectrum' feature.
> > 
> > This patchset properly set the bit responsible for the spread spectrum
> > in the mpll driver and add the required correction in the related clock
> > controllers.
> > 
> > Jerome Brunet (3):
> >   clk: meson: mpll: properly handle spread spectrum
> this depends on a patch from your other series "clk: meson: fixup g12a
> mpll": [0]
> personally I would base the other series on this one because this one
> contains a "Fixes" that (meaning that the patch will get backported
> and that's easier if there aren't any conflicts)

1) The other series [0] had been submitted before we knew about the fix which
is why this one is based on it.
2) Considering the amount of work that went through since the fixed commit, I
doubt it makes much of a difference.

I might do it if both series require a resend.

> 
> 
> Regards
> Martin
> 
> 
> [0] https://patchwork.kernel.org/patch/10868837/