drm/xen-zcopy: Add Xen zero-copy helper DRM driver

From: Oleksandr Andrushchenko <[email protected]>

Hello!

When using Xen PV DRM frontend driver then on backend side one will need to do copying of display buffers' contents (filled by the frontend's user-space) into buffers allocated at the backend side. Taking into account the size of display buffers and frames per seconds it may result in unneeded huge data bus occupation and performance loss.

This helper driver allows implementing zero-copying use-cases when using Xen para-virtualized frontend display driver by implementing a DRM/KMS helper driver running on backend's side. It utilizes PRIME buffers API to share frontend's buffers with physical device drivers on backend's side:

- a dumb buffer created on backend's side can be shared with the Xen PV frontend driver, so it directly writes into backend's domain memory (into the buffer exported from DRM/KMS driver of a physical display device)
- a dumb buffer allocated by the frontend can be imported into physical device DRM/KMS driver, thus allowing to achieve no copying as well

For that reason number of IOCTLs are introduced:
- DRM_XEN_ZCOPY_DUMB_FROM_REFS
This will create a DRM dumb buffer from grant references provided by the frontend
- DRM_XEN_ZCOPY_DUMB_TO_REFS
This will grant references to a dumb/display buffer's memory provided by the backend
- DRM_XEN_ZCOPY_DUMB_WAIT_FREE
This will block until the dumb buffer with the wait handle provided be freed

With this helper driver I was able to drop CPU usage from 17% to 3% on Renesas R-Car M3 board.

This was tested with Renesas' Wayland-KMS and backend running as DRM master.

Thank you,
Oleksandr

Oleksandr Andrushchenko (1):
drm/xen-zcopy: Add Xen zero-copy helper DRM driver

 Documentation/gpu/drivers.rst               |   1 +
 Documentation/gpu/xen-zcopy.rst             |  32 +
 drivers/gpu/drm/xen/Kconfig                 |  25 +
 drivers/gpu/drm/xen/Makefile                |   5 +
 drivers/gpu/drm/xen/xen_drm_zcopy.c         | 880 ++++++++++++++++++++++++++++
 drivers/gpu/drm/xen/xen_drm_zcopy_balloon.c | 154 +++++
 drivers/gpu/drm/xen/xen_drm_zcopy_balloon.h |  38 ++
 include/uapi/drm/xen_zcopy_drm.h            | 129 ++++
 8 files changed, 1264 insertions(+)
 create mode 100644 Documentation/gpu/xen-zcopy.rst
 create mode 100644 drivers/gpu/drm/xen/xen_drm_zcopy.c
 create mode 100644 drivers/gpu/drm/xen/xen_drm_zcopy_balloon.c
 create mode 100644 drivers/gpu/drm/xen/xen_drm_zcopy_balloon.h
 create mode 100644 include/uapi/drm/xen_zcopy_drm.h

2.16.2

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