Precise vblank timestamping is implemented via the
usual scanout position based method. On VC4 the
pixelvalves PV do not have a scanout position
register. Only the hardware video scaler HVS has a
similar register which describes which scanline for
the output is currently composited and stored in the
HVS fifo for later consumption by the PV.
This causes a problem in that the HVS runs at a much
faster clock (system clock / audio gate) than the PV
which runs at video mode dot clock, so the unless the
fifo between HVS and PV is full, the HVS will progress
faster in its observable read line position than video
scan rate, so the HVS position reading can't be directly
translated into a scanout position for timestamp correction.
Additionally when the PV is in vblank, it doesn't consume
from the fifo, so the fifo gets full very quickly and then
the HVS stops compositing until the PV enters active scanout
and starts consuming scanlines from the fifo again, making
new space for the HVS to composite.
Therefore a simple translation of HVS read position into
elapsed time since (or to) start of active scanout does
not work, but for the most interesting cases we can still
get useful and sufficiently accurate results:
1. The PV enters active scanout of a new frame with the
fifo of the HVS completely full, and the HVS can refill
any fifo line which gets consumed and thereby freed up by
the PV during active scanout very quickly. Therefore the
PV and HVS work effectively in lock-step during active
scanout with the fifo never having more than 1 scanline
freed up by the PV before it gets refilled. The PV's
real scanout position is therefore trailing the HVS
compositing position as scanoutpos = hvspos - fifosize
and we can get the true scanoutpos as HVS readpos minus
fifo size, so precise timestamping works while in active
scanout, except for the last few scanlines of the frame,
when the HVS reaches end of frame, stops compositing and
the PV catches up and drains the fifo. This special case
would only introduce minor errors though.
2. If we are in vblank, then we can only guess something
reasonable. If called from vblank irq, we assume the irq is
usually dispatched with minimum delay, so we can take a
timestamp taken at entry into the vblank irq handler as a
baseline and then add a full vblank duration until the
guessed start of active scanout. As irq dispatch is usually
pretty low latency this works with relatively low jitter and
good results.
If we aren't called from vblank then we could be anywhere
within the vblank interval, so we return a neutral result,
simply the current system timestamp, and hope for the best.
Measurement shows the generated timestamps to be rather precise,
and at least never off more than 1 vblank duration worst-case.
Limitations: Doesn't work well yet for interlaced video modes,
therefore disabled in interlaced mode for now.
v2: Use the DISPBASE registers to determine the FIFO size (changes
by anholt)
Signed-off-by: Mario Kleiner <mario.kleiner.de@gmail.com>
Signed-off-by: Eric Anholt <eric@anholt.net>
Reviewed-and-tested-by: Mario Kleiner <mario.kleiner.de@gmail.com> (v2)
Protect both the setup of the pageflip event and the
latching of the new requested displaylist head pointer
by the event lock, so we can't get into a situation
where vc4_atomic_flush latches the new display list via
HVS_WRITE, then immediately gets preempted before queueing
the pageflip event, then the page-flip completes in hw and
the vc4_crtc_handle_page_flip() runs and no-ops due to
lack of a pending pageflip event, then vc4_atomic_flush
continues and only then queues the pageflip event - after
the page flip handling already no-oped. This would cause
flip completion handling only at the next vblank - one
frame too late.
In vc4_crtc_handle_page_flip() check the actual DL head
pointer in SCALER_DISPLACTX against the requested pointer
for page flip to make sure that the flip actually really
completed in the current vblank and doesn't get deferred
to the next one because the DL head pointer was written
a bit too late into SCALER_DISPLISTX, after start of
vblank, and missed the boat. This avoids handling a
pageflip completion too early - one frame too early.
According to Eric, DL head pointer updates which were
written into the HVS DISPLISTX reg get committed to hardware
at the last pixel of active scanout. Our vblank interrupt
handler, as triggered by PV_INT_VFP_START irq, gets to run
earliest at the first pixel of HBLANK at the end of the
last scanline of active scanout, ie. vblank irq handling
runs at least 1 pixel duration after a potential pageflip
completion happened in hardware.
This ordering of events in the hardware, together with the
lock protection and SCALER_DISPLACTX sampling of this patch,
guarantees that pageflip completion handling only runs at
exactly the vblank irq of actual pageflip completion in all
cases.
Background info from Eric about the relative timing of
HVS, PV's and trigger points for interrupts, DL updates:
https://lists.freedesktop.org/archives/dri-devel/2016-May/107510.html
Tested on RPi 2B with hardware timing measurement equipment
and shown to no longer complete flips too early or too late.
Signed-off-by: Mario Kleiner <mario.kleiner.de@gmail.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
We could possibly save a bit of power by not requesting gamma
conversion when the ramp happens to be 1:1, but at least if all the
CRTCs are off the SRAM will be disabled.
This should fix brightness sliders in a lot of fullscreen games.
Signed-off-by: Eric Anholt <eric@anholt.net>
This pull request fixes the major VC4 HDMI modesetting bugs found when
the first wave of users showed up in Raspbian.
* tag 'drm-vc4-fixes-2016-03-03' of github.com:anholt/linux:
drm/vc4: Initialize scaler DISPBKGND on modeset.
drm/vc4: Fix setting of vertical timings in the CRTC.
drm/vc4: Fix the name of the VSYNCD_EVEN register.
drm/vc4: Add another reg to HDMI debug dumping.
drm/vc4: Bring HDMI up from power off if necessary.
drm/vc4: Fix a framebuffer reference leak on async flip interrupt.
We weren't updating the interlaced bit, so we'd scan out incorrectly
if the firmware had brought up the TV encoder and we were switching to
HDMI.
Signed-off-by: Eric Anholt <eric@anholt.net>
If the firmware hadn't brought up HDMI for us, we need to do its
power-on reset sequence (reset HD and and clear its STANDBY bits,
reset HDMI, and leave the PHY disabled).
Signed-off-by: Eric Anholt <eric@anholt.net>
This supports 420 and 422 subsampling with 2 or 3 planes, tested with
modetest. It doesn't set up chroma subsampling position (which it
appears KMS doesn't deal with yet).
The LBM memory is overallocated in many cases, but apparently the docs
aren't quite correct and I'll probably need to look at the hardware
source to really figure it out.
Signed-off-by: Eric Anholt <eric@anholt.net>
This implements a simple policy for choosing scaling modes
(trapezoidal for decimation, PPF for magnification), and a single PPF
filter (Mitchell/Netravali's recommendation).
Signed-off-by: Eric Anholt <eric@anholt.net>
This is enough for fbcon and bringing up X using
xf86-video-modesetting. It doesn't support the 3D accelerator or
power management yet.
v2: Drop FB_HELPER select thanks to Archit's patches. Do manual init
ordering instead of using the .load hook. Structure registration
more like tegra's, but still using the typical "component" code.
Drop no-op hooks for atomic_begin and mode_fixup() now that
they're optional. Drop sentinel in Makefile. Fix minor style
nits I noticed on another reread.
v3: Use the new bcm2835 clk driver to manage pixel/HSM clocks instead
of having a fixed video mode. Use exynos-style component driver
matching instead of devicetree nodes to list the component driver
instances. Rename compatibility strings to say bcm2835, and
distinguish pv0/1/2. Clean up some h/vsync code, and add in
interlaced mode setup. Fix up probe/bind error paths. Use
bitops.h macros for vc4_regs.h
v4: Include i2c.h, allow building under COMPILE_TEST, drop msleep now
that other bugs have been fixed, add timeouts to cpu_relax()
loops, rename hpd-gpio to hpd-gpios.
Signed-off-by: Eric Anholt <eric@anholt.net>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
