Hi 2012/12/8 Damien Lespiau <damien.lespiau at intel.com>: > On Sat, Dec 1, 2012 at 2:04 PM, Paulo Zanoni <przanoni at gmail.com> wrote: >> From: Paulo Zanoni <paulo.r.zanoni at intel.com> >> >> If we fail to set the bit when needed we get some nice FDI link >> training failures (AKA "black screen on VGA output"). >> >> While we don't really know how to properly choose whether we need to >> set the bit or not (VBT?), just read the initial value set by the BIOS >> and store it for later usage. >> >> Signed-off-by: Paulo Zanoni <paulo.r.zanoni at intel.com> > > Sad that we did not catch that before. It's not just the polarity > (support for exchanging the - and + wires on a differential pair), but > also the FDI lane reversal (0 becomes 3, 1 becomes 2) setting that we > need to preserve. There's a fused bit for the DMI lane reversal and > FDI defaults to following that DMI lane reversal configuration, but we > also have a bit to override that behaviour in the FDI RX register, we > need to preserve this bit as well. They're different problems and require different patches. This one fixes the "FDI RX polarity" problem, not "lane reversal". > > I think this is the same story for DDI_BUF_CTL, DDI ports support lane reversal. > > I could not find either where these settings are stored, preserving > what the BIOS does for those seems the best option so far. > > -- > Damien -- Paulo Zanoni
