On Mon, Mar 27, 2017 at 12:11:12PM +0100, Martyn Welch wrote: > On Fri, Mar 24, 2017 at 11:42:53AM +0100, Philipp Zabel wrote: > > On Fri, 2017-03-24 at 10:24 +0000, Martyn Welch wrote: > > [...] > > > > Could you move to v4.9 or v4.10 and check if the four patches in > > > > https://git.pengutronix.de/cgit/pza/linux/tag/?id=v4.9-ipu-dp-plane-fix > > > > or > > > > https://git.pengutronix.de/cgit/pza/linux/tag/?id=v4.10-ipu-dp-plane-fix-2 > > > > help? > > > > > > > > > > I've updated to v4.10, the patches from v4.10-ipu-dp-plane-fix-2 resolve > > > the error, though we are unfortunately still experiencing the loss of > > > output on LVDS display. Time to look elsewhere for the cause of that I > > > guess. :-) > > > > Is the LVDS serial clock derived from the video PLL on that board? > > (What is the output of /sys/kernel/debug/clk/clk_summary?) > > > > I beleive so. I've included a few dumps from clk_summary below. > After looking at the dumps in more detail, I think I know what's happening: Problem appears to be a clocking issue. When we have a display connected to the HDMI port pre-boot, it uses the following chain to drive IPU2 (which is used for this display): PLL5(756000000) -> PLL5_POST_DIV(756000000/2) -> PLL5_VIDEO_DIV(378000000/1) -> LDB_DI1_IPU_DIV(378000000/3.5) -> LDB_DI1(108000000) -> IPU2_DI0(108000000) If the display connected via the LVDS interface is connected either before or after boot, we end up with IPU1 being drive thus: PLL2_PFD2(432000000) -> IPU2_DI1_PRE_CLK(432000000) -> IPU2DI1_PODF(432000000/4) -> IPU1_DI0(108000000) On the other hand, if only the LVDS is connected at boot, instead it is sets up IPU1 as follows: PLL5(756000000) -> PLL5_POST_DIV(756000000/2) -> PLL5_VIDEO_DIV(378000000/1) -> LDB_DI1_IPU_DIV(378000000/3.5) -> LDB_DI1(108000000) -> IPU1_DI0(108000000) Which interestingly matches how IPU2 is configured previously. When the HDMI interface is then connected it does this to configure IPU2: PLL5(864000000) -> PLL5_POST_DIV(756000000/4) -> PLL5_VIDEO_DIV(216000000/2) -> IPU2DI0_PODF(108000000/1) -> IPU2_DI0(108000000) But as the path "PLL5 -> PLL5_POST_DIV -> PLL5_VIDEO_DIV" is shared with IPU1 the change in frequency and divider values results in: PLL5(864000000) -> PLL5_POST_DIV(756000000/4) -> PLL5_VIDEO_DIV(216000000/2) -> LDB_DI1_IPU_DIV(108000000/3.5) -> LDB_DI1(30857142) -> IPU1_DI0(30857142) So the LVDS Bridge and IPU1 are now underclocked by 3.5 times. I suspect that (theoretically) as IPU1_DI0 is already configured at the required frequency via LDB_DI1, it might have been sufficient for the IPU2_DI0_SEL MUX to select LDB_DI1 as its source? Martyn _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
