On Fri, 30 Sep 2011 18:32:35 +0200, Daniel Vetter <daniel@xxxxxxxx> wrote: > Ok, this is way over my head, just checked whether the patch does what it > claims to - nice exercise in reading dp modeset code ;-) Yeah, it's purely heuristic -- the VBT contains a mode which was originally for the LVDS. It's unclear whether it should ever be applied to an eDP panel, but absent other information, it seems like we should at least consider it. Many LVDS panels don't bother to include an EDID rom, or the vendor didn't bother to hook up the DDC wire; presumably it's cheaper for them to stick more data in the VBIOS than add hardware. However, there are some LVDS panels with EDID roms which contain *incorrect* mode data for the panel (amazing, I know), and so the driver prefers to use the VBT data when both are present. eDP, on the other hand, doesn't require any additional wiring (at least) to connect up the DDC channel, and eDP panels are required to provide EDID data. So far, in my (very small) sample set, I've got one machine which provides accurate VBT *and* EDID data (an HP 2540p) and one machine which provides inaccurate VBT data but accurate EDID data (a MacBook air). So, I just decided to prefer the EDID data. One option would be to extract the current mode from the hardware when the driver starts and use that if present. But, that might mean that you'd get different modes depending on whether the machine booted with the lid closed or open, which seems like a bad plan. -- keith.packard@xxxxxxxxx
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