[v2,0/3] Rate-limit shadow-FB-to-console-update to screen refresh

Message

Thomas Zimmermann Sept. 12, 2019, 6:42 a.m. UTC

A full-screen memcpy() moves the console's shadow buffer to hardware; with
possibly significant runtime overhead. [1]

The console's dirty worker now waits for the vblank to rate limit the
output frequency. Screen output can pile up while waiting and there's a
chance that multiple screen updates can be handled with a single memcpy().
Note that this has no effect on tearing: while the dirty worker updates
the hardware buffer, new data can still arrive in the shadow buffer. This
can create a tearing effcet, even though console output is synchronized
to vblank.

The patchset adds vblank support to mgag200, because the problem was first
reported with Matrox hardware.

v2:
	* remove locking from fbdev patch
	* use constants fro mgag200 register names and fields
	* double-check that VLINE irq is active on mgag200
	* only signal vblank on CRTC 0 of mgag200
	* coding-style fixes

[1] https://lists.freedesktop.org/archives/dri-devel/2019-July/228663.html

Thomas Zimmermann (3):
  drm/fb-helper: Synchronize dirty worker with vblank
  drm/mgag200: Rename constant MGAREG_Status to MGAREG_STATUS
  drm/mgag200: Add vblank support

 drivers/gpu/drm/drm_fb_helper.c        | 10 +++++
 drivers/gpu/drm/mgag200/mgag200_drv.c  |  1 +
 drivers/gpu/drm/mgag200/mgag200_drv.h  |  1 +
 drivers/gpu/drm/mgag200/mgag200_main.c | 40 +++++++++++++++++++
 drivers/gpu/drm/mgag200/mgag200_mode.c | 53 ++++++++++++++++++++++----
 drivers/gpu/drm/mgag200/mgag200_reg.h  |  7 +++-
 6 files changed, 104 insertions(+), 8 deletions(-)

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2.23.0