On Fri, Dec 02, 2016 at 05:43:43PM +0200, Laurent Pinchart wrote: > DW_HDMI_QUIRK_FC_INVIDCONF is indeed a bad name, I'll fix that. > > Do you know why this function needs to write to the HDMI_FC_INVIDCONF > register four times in the normal case, and once only for IMX6DL ? (I don't have much time at present, I'm buried in ARM64 crud trying to get a platform to boot, and working out how to debug an ARM64 platform that even earlycon doesn't work on... no printascii() types of easy debug facilities on ARM64 make this job several orders of magnitude harder than it needs to be...) It prevents a magenta line down the left hand side of the screen, which is caused when the frame composer in the HDMI Tx gets confused - according to the errata, it does a load of maths when you write to the frame composer registers, and sometimes it doesn't update properly. So, the four writes (and the number is critical) is there to persuade the IP to do the maths with the right values so the internal timings are correct. The rather confusing thing is - it's actually IMX6Q which has the more severe errata, not IMX6DL - the workaround of four writes is applied in the 6Q case. It's covered by ERR004308 in the IMX6Q Errata document (search for IMX6DQCE). It isn't mentioned in the IMX6DL documentation, but it seems that similar workaround of one write is necessary there. Some of this was determined by experimentation in conjunction with the errata documentation - I remember it took a while to get it right so that we didn't ever see the magenta line. -- RMK's Patch system: http://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up according to speedtest.net. _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
