Is "perfectly equal monitors" really required to reclock MCLK

[Alex Deucher]

On Fri, Jan 13, 2023 at 10:05 AM Braiam <braiamp at gmail.com> wrote:
>
> AMD RX 590. Forgot to include it. How do I know the blanking period?

OK polaris falls into the first bucket.  Look at the full modelines.
E.g., xrandr --verbose.

> Would variable refresh rate mess up with that?

Probably.

Alex

>
> On Fri, Jan 13, 2023 at 10:57 AM Alex Deucher <alexdeucher at gmail.com> wrote:
> >
> > On Fri, Jan 13, 2023 at 9:47 AM Braiam <braiamp at gmail.com> wrote:
> > >
> > > Hi,
> > >
> > > I have two monitors with the current following configuration:
> > >
> > > Screen 0: minimum 320 x 200, current 5120 x 1440, maximum 16384 x 16384
> > > DisplayPort-0 connected primary 2560x1440+0+0 (normal left inverted
> > > right x axis y axis) 597mm x 336mm
> > >    2560x1440    164.83 +  59.95 + 120.05*   96.01    72.01    60.01
> > > 143.97   120.00    74.97
> > > [snip]
> > > DisplayPort-1 connected 2560x1440+2560+0 (normal left inverted right x
> > > axis y axis) 597mm x 336mm
> > >    2560x1440    165.00 +  59.95 + 120.06*   96.04    72.01    60.01
> > > 50.01    48.01   144.00   119.99    99.99
> > > [snip]
> > > HDMI-A-0 disconnected (normal left inverted right x axis y axis)
> > > HDMI-A-1 disconnected (normal left inverted right x axis y axis)
> > > DVI-D-0 disconnected (normal left inverted right x axis y axis)
> > >
> > > The pp_profile_mode:
> > >
> > > NUM        MODE_NAME     SCLK_UP_HYST   SCLK_DOWN_HYST
> > > SCLK_ACTIVE_LEVEL     MCLK_UP_HYST   MCLK_DOWN_HYST MCLK_ACTIVE_LEVEL
> > >   0   BOOTUP_DEFAULT:        -                -                -
> > >          -                -                -
> > >   1 3D_FULL_SCREEN *:        0              100               30
> > >         10               60               25
> > >   2     POWER_SAVING:       10                0               30
> > >          -                -                -
> > >   3            VIDEO:        -                -                -
> > >         10               16               31
> > >   4               VR:        0               11               50
> > >          0              100               10
> > >   5          COMPUTE:        0                5               30
> > >          -                -                -
> > >   6           CUSTOM:        -                -                -
> > >          -                -                -
> > >
> > > I have set their refresh rate to 72.01 which is a mode equal for both,
> > > and the MCLK wasn't downclocked either. They are branded HP and
> > > Scepter. Using a vtty doesn't help either.
> > >
> > > Is having the exact same monitor really required? If not, how can I
> > > check what is causing
> > > the memory clock to be pegged that high?
> >
> > It depends what GPU you have.  Older ones can only reclock memory
> > during the vertical blanking period assuming it's long enough as the
> > whole reclocking process takes a certain amount of time.  If it
> > doesn't happen during the blanking period you will get visible
> > glitches on the screen when the reclock happens.  If the vertical
> > blanking period is not long enough or if the vblank periods are not
> > aligned when using multiple monitors, the driver doesn't reclock.  The
> > mode lines (not just the refresh rate) have to be the exact same for
> > the vblanks to line up when using multiple monitors.  Your best bet is
> > to take the mode line you want to use from one monitor and apply it to
> > the other monitor.  Newer GPUs have more flexibility and can reclock
> > memory in more situations, but there are still some monitors where the
> > timing may not work out.
> >
> > What GPU do you have?
> >
> > Alex
>
>
>
> --
> Braiam