Bug 19236

Summary: Radeon r300 overlay resolution and pixel clock
Product: xorg Reporter: Tobias Diedrich <ranma+freedesktop>
Component: Driver/RadeonAssignee: xf86-video-ati maintainers <xorg-driver-ati>
Status: RESOLVED NOTABUG QA Contact: Xorg Project Team <xorg-team>
Severity: normal    
Priority: medium    
Version: git   
Hardware: All   
OS: All   
Whiteboard:
i915 platform: i915 features:

Description Tobias Diedrich 2008-12-22 07:57:47 UTC 
For pixel clocks above 175MHz the backend scaler overlay resolution is halved.
I suspect maybe a hardware limitation of older chips only.
On my r300, after patching radeon_video.c so that ecp_div is always 0, the overlay looks much better now (Using a custom 1680x1050@72 modeline, which unfortunately has a pixel clock above 175MHz).
Now I'm not sure if this means I'm overclocking the backend scaler.
But the scaler seems to work just fine at this setting, so maybe this is only required for older chips?

My custom modeline:
Modeline "1680x1050@72" 198.36 1680 1712 2464 2496 1050 1070 1082 1103

Default monitor modeline:
(II) RADEON(0): Modeline "1680x1050"x0.0  146.25  1680 1784 1960 2240  1050 1053 1059 1089 -hsync +vsync (65.3 kHz)

The custom modeline was generated with xtiming.sf.net, I wanted a 72Hz modeline because I usually watch 24Hz videos and expect that a refresh rate of 72Hz is a better match than 60Hz for this.
Comment 1 Roland Scheidegger 2008-12-22 08:30:25 UTC 
Even r300 docs mention that ecp divider should be set above 175Mhz, though I guess newer chips are more likely to succeed overclocking the scaler than older ones (or it could just be in the docs because it was not updated).
Though in your case I guess you could generate a modeline with reduced blanking, I think even at 72 hz it would be below 175Mhz. I don't think reduced blanking is actually specified for anything else than 60Hz, but the monitor might still accept it.

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