Thanks Ville! Learned from you guys. :)
于 09/06/15 19:50, Ville Syrjälä 写道:
On Sun, Sep 06, 2015 at 07:30:26PM +0800, Zhi Wang wrote:
Hi William:
There is a kind of display register marked as double-buffered. It
means that HW will *not* latch the value in the register all the time.
HW will only latch the value on the start of the vertical blank, or the
time when pipe/plane are enabling.
So you will see some code pieces are waiting for frame count change
after updating a register.
For WM registers, it should be double-buffered with armed attribute I
believe.
Only since SKL. Before that WM registers weren't double buffered.
It means after writing the WM registers, you have to write
another register to let the WM register become into "armed" state. After
the register is "armed", HW will latch the value on the time point
mentioned above.
So you should see in some code pieces, they write another register after
updating the target register, then waits for the frame count change.
i.e update WM register -> update PLANE SURF register -> wait for frame
count change
于 09/03/15 06:42, Xie, William 写道:
Hi all,
Can anyone educate me if water mark update need to wait for next VSYNC?
In other words, if we flip a frame to overlay for the first time,
it will be showed in the next VBlank as water mark update needs to wait
for that?
Is this true or a bug?
Thanks
William
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