What's the difference if double-buffered with armed attribute? William -----Original Message----- From: Ville Syrjälä [mailto:ville.syrjala@xxxxxxxxxxxxxxx] Sent: Sunday, September 06, 2015 7:50 PM To: Wang, Zhi A Cc: Xie, William; intel-gfx@xxxxxxxxxxxxxxxxxxxxx Subject: Re: Water mark update need to wait for next VSYNC? 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 > > > > > > > > _______________________________________________ > > Intel-gfx mailing list > > Intel-gfx@xxxxxxxxxxxxxxxxxxxxx > > http://lists.freedesktop.org/mailman/listinfo/intel-gfx > > > _______________________________________________ > Intel-gfx mailing list > Intel-gfx@xxxxxxxxxxxxxxxxxxxxx > http://lists.freedesktop.org/mailman/listinfo/intel-gfx -- Ville Syrjälä Intel OTC _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/intel-gfx
