I have a large CRT monitor with a maximum resolution (as claimed by EDID) of 1600x1200. If I try to start X with an xorg.conf that requests 1600x1200 as the initial resolution (or if I start it without an xorg.conf), then the server crashes with > (II) CHROME(0): Required bandwidth is not available. (576000000 > 553000000) > (II) CHROME(0): ViaDisplayDisableCRT > (EE) > Fatal server error: > (EE) AddScreen/ScreenInit failed for driver 0 However, if I start X with an xorg.conf that requests a lower resolution (e.g. 1280x1024), and if I later request 1600x1200 with > $ xrandr --output VGA-1 --mode "1600x1200" then the server accepts and switches to the higher resolution without complaint. Openchrome 0.3.3 (as packaged in Debian testing) Xorg server 1.16.2 RC 1 (also from Debian) Logs and example attachments comming.
Created attachment 110522 [details] maxres.Xorg.log Attaching Xorg.log from the X server's failed attempt to startup with a xorg.conf that requests 1600x1200 as the inital resolution. I also get the same result (and almost exactly the same log) when starting X with no xorg.conf.
Created attachment 110523 [details] maxres.xorg.conf The xorg.conf used to generate maxres.Xorg.log.
Created attachment 110524 [details] workaround.Xorg.log The Xorg.log from a successful X server start with an xorg.conf requesting 1280x1024 as the inital resolution, followed by a successful switch to 1600x1200 via xrandr.
Created attachment 110525 [details] workaround.xorg.conf The xorg.conf used to generate workaround.Xorg.log
I think what happens is the following : the initial resolution is set to 1600x1200@75Hz, which exceed the memory bandwidth limit. When xrandr set the resolution, it set the mode to 1600x1200 @60Hz, which does not exceed the bandwidth. The 1600x1200@75 mode is validated in iga1_crtc_mode_fixup by ViaFirstCRTCModeValid, but then rejected by the later bandwidth check. One would expect it then fallback to the next available mode in the EDID, that is 1600x1200@60, but it seems that doesn't happen. I'll try to dig more to understand what happens, but I'm stuck for now.
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