Hello, On Friday 02 Dec 2016 18:45:46 Laurent Pinchart wrote: > On Friday 02 Dec 2016 16:08:17 Russell King - ARM Linux wrote: > > 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...) > > Thanks all the more for taking time to reply. > > > 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. > > That's interesting. I'll test the different options on my Renesas platform > (no write, one write, four writes) and see what is needed. Could anyone > perform the same tests on a Rockchip RK3288 system ? Daniel Stone has been nice enough to test HDMI output without the errata workaround on RK3288 and hasn't noticed any issue. I've performed the same test on R-Car H3 and haven't noticed any issue either. The i.MX6DL and i.MX6Q use a DWC HDMI TX version 1.31a and 1.30a respectively, while RK3288 and R-Car H3 uses v2.00a and v2.01a. We could enable the workaround based on the HDMI TX version. -- Regards, Laurent Pinchart
