[PATCH v2 0/3] A DRM API for adaptive sync and variable refresh rate support

Wed Oct 3 08:25:42 UTC 2018

Hi

I'm curious to know whether this will/could work over PRIME

If the discrete card is rendering slower than the display's frequency could
the frequency be dropped on integrated display? I think there are laptops
that have freesync now

Cheers

Mike

On Mon, 1 Oct 2018 at 08:15 Daniel Vetter <daniel at ffwll.ch> wrote:

> On Mon, Sep 24, 2018 at 02:15:34PM -0400, Nicholas Kazlauskas wrote:
> > These patches are part of a proposed new interface for supporting
> variable refresh rate via DRM properties.
> >
> > === Changes from v1 ===
> >
> > For drm:
> >
> > * The variable_refresh_capable property is now flagged as
> DRM_MODE_PROP_IMMUTABLE
> >
> > For drm/gpu/amd/display:
> >
> > * Patches no longer pull in IOCTL/FreeSync refactoring code
> > * FreeSync enable/disable behavior has been modified to reflect changes
> in userspace behavior from xf86-video-amdgpu and mesa
> >
> > === Adaptive sync and variable refresh rate ===
> >
> > Adaptive sync is part of the DisplayPort spec and allows for graphics
> adapters to drive displays with varying frame timings.
> >
> > Variable refresh rate (VRR) is essentially the same, but defined for
> HDMI.
> >
> > === Use cases for variable refresh rate ===
> >
> > Variable frame (flip) timings don't align well with fixed refresh rate
> displays. This results in stuttering, tearing and/or input lag. By
> adjusting the display refresh rate dynamically these issues can be reduced
> or eliminated.
> >
> > However, not all content is suitable for dynamic refresh adaptation.
> Content that is flipped infrequently or at random intervals tends to fair
> poorly. Multiple clients trying to flip under the same screen can similarly
> interfere with prediction.
> >
> > Userland needs a way to let the driver know when the content on the
> screen is suitable for variable refresh rate and if the user wishes to have
> the feature enabled.
> >
> > === DRM API to support variable refresh rates ===
> >
> > This patch introduces a new API via atomic properties on the DRM
> connector and CRTC.
> >
> > The connector has two new optional properties:
> >
> > * bool variable_refresh_capable - set by the driver if the hardware is
> capable of supporting variable refresh tech
> >
> > * bool variable_refresh_enabled - set by the user to enable variable
> refresh adjustment over the connector
> >
> > The CRTC has one additional default property:
> >
> > * bool variable_refresh - a content hint to the driver specifying that
> the CRTC contents are suitable for variable refresh adjustment
> >
> > == Overview for DRM driver developers ===
> >
> > Driver developers can attach the optional connector properties via
> drm_connector_attach_variable_refresh_properties on connectors that support
> variable refresh (typically DP or HDMI).
> >
> > The variable_refresh_capable property should be managed as the output on
> the connector changes. The property is read only from userspace.
> >
> > The variable_refresh_enabled property is intended to be a property
> controlled by userland as a global on/off switch for variable refresh
> technology. It should be checked before enabling variable refresh rate.
> >
> > === Overview for Userland developers ==
> >
> > The variable_refresh property on the CRTC should be set to true when the
> CRTCs are suitable for variable refresh rate. In practice this is probably
> an application like a game - a single window that covers the whole CRTC
> surface and is the only client issuing flips.
> >
> > To demonstrate the suitability of the API for variable refresh and
> dynamic adaptation there are additional patches using this API that
> implement adaptive variable refresh across kernel and userland projects:
> >
> > * DRM (dri-devel)
> > * amdgpu DRM kernel driver (amd-gfx)
> > * xf86-video-amdgpu (amd-gfx)
> > * mesa (mesa-dev)
> >
> > These patches enable adaptive variable refresh on X for AMD hardware
> provided that the user sets the variable_refresh_enabled property to true
> on supported connectors (ie. using xrandr --set-prop).
> >
> > The patches have been tested as working on upstream userland with the
> GNOME desktop environment under a single monitor setup. They also work on
> KDE in single monitor setup if the compositor is disabled.
> >
> > The patches require that the application window can issue screen flips
> via the Present extension to xf86-video-amdgpu. Due to Present extension
> limitations some desktop environments and multi-monitor setups are
> currently not compatible.
> >
> > Full implementation details for these changes can be reviewed in their
> respective mailing lists.
> >
> > === Previous discussions ===
> >
> > These patches are based upon feedback from patches and feedback from two
> previous threads on the subject which are linked below for reference:
> >
> > https://lists.freedesktop.org/archives/amd-gfx/2018-April/021047.html
> >
> https://lists.freedesktop.org/archives/dri-devel/2017-October/155207.html
> >
> https://lists.freedesktop.org/archives/dri-devel/2018-September/189404.html
> >
> > Nicholas Kazlauskas
> >
> > Nicholas Kazlauskas (3):
> >   drm: Add variable refresh rate properties to connector
> >   drm: Add variable refresh property to DRM CRTC
> >   drm/amd/display: Set FreeSync state using DRM VRR properties
>
> Please include Manasi manasi.d.navare at intel.com when resending, she's
> working on this from our side.
>
> Also some overview kernel-docs that document the uapi aspect of how the
> prorties are driven should be included. Probably best if you add a new
> "Variable Refresh Rate" section under
>
> https://dri.freedesktop.org/docs/drm/gpu/drm-kms.html#kms-properties
>
> with links to functions drivers should call to set up and everything. Best
> practice is to stuff all that into a DOC: comment.
>
> An igt testcase would be neat too.
>
> Cheers, Daniel
>
> >
> >  .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 232 +++++++++---------
> >  .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.h |   6 +-
> >  drivers/gpu/drm/drm_atomic_helper.c           |   1 +
> >  drivers/gpu/drm/drm_atomic_uapi.c             |  12 +
> >  drivers/gpu/drm/drm_connector.c               |  35 +++
> >  drivers/gpu/drm/drm_crtc.c                    |   2 +
> >  drivers/gpu/drm/drm_mode_config.c             |   6 +
> >  include/drm/drm_connector.h                   |  27 ++
> >  include/drm/drm_crtc.h                        |  13 +
> >  include/drm/drm_mode_config.h                 |   8 +
> >  10 files changed, 225 insertions(+), 117 deletions(-)
> >
> > --
> > 2.19.0
> >
>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch
> _______________________________________________
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> dri-devel at lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel
>
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