On Thu, 8 Dec 2011 13:41:53 -0200, przanoni at gmail.com wrote: > From: Paulo Zanoni <paulo.r.zanoni at intel.com> > > We use struct intel_sdvo_dtd for that too. > > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=15766 > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=42174 > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=43333 > > Signed-off-by: Paulo Zanoni <paulo.r.zanoni at intel.com> I think the patch this is sort-of-reverting was wrong. Here's what I found: It was non-obvious to me what vblank high/low would mean on a digital link. It turns out that there are 3 magic characters sent down instead of pixel data: blank, hsync, and vsync (and syncs can overlap). The sync polarity field for SDVOB in the PRM (looking at G35 here) says: "Indicates the polarity of Hsync and Vsync. Inverted polarity is transmitted as SYNC-BLANK-SYNC and standard polarity is transmitted as BLANK-SYNC-BLANK. For example, if Vsync is not inverted and Hsync is inverted, an Hsync period transmitted during Vsync would be transmitted as BLANK+VS+HS ? BLANK+VS ? BLANK+VS+HS." Looking at my SDVO EDS, there's an example of "Invalid HSync Blank Periods", which includes a sample sequence of "active blank+ hsync blank hsync blank+ active" being invalid, which matches that description for hsync low. The valid hsync examples all match "active blank+ hsync+ blank+ active". (+ here is the regexp meaning of "at least one of the character"). I don't see equivalent examples banning vertical low, but I'd expect so (the valid vertical example is vertical high). However, I think setting these flags pre-gen4 is also wrong -- bit 4 is reserved and bit 3 is RO and has a different meaning. I think the pure revert is the right answer, instead. A couple of interesting notes for people debugging SDVO that aren't reflected in our code: vblank must be at least 3 lines vsync must be at least one line. hblank must be at least hsync characters hsync must be at least 16 characters. -------------- next part -------------- A non-text attachment was scrubbed... Name: not available Type: application/pgp-signature Size: 197 bytes Desc: not available URL: <http://lists.freedesktop.org/archives/intel-gfx/attachments/20111208/3bbb0d59/attachment.pgp>
