I've run into a problem setting display modes. I'm attempting to output
3840x2160 @ 60Hz to a hardware recorder but the standard modes for 60Hz and
59.94Hz actually come out to 60.02Hz and 59.98Hz. EDID data has 1080p@60 as
it's preferred mode, and scaling the numbers up leads to the same rounding
error (60.02Hz) as the predefined modes have.
Here's the modeline that has the incorrect refresh rate:
"3840x2160" 594.18 3840 4016 4104 4400 2160 2168 2178 2250
Here's how it's defined in kernel_source/drivers/video/modedb.c:
{.refresh = 60, .xres = 3840, .yres = 2160, .pixclock = 1683,
.left_margin = 296, .right_margin = 176,
.upper_margin = 72, .lower_margin = 8,
.hsync_len = 88, .vsync_len = 10,
.sync = FB_SYNC_HOR_HIGH_ACT | FB_SYNC_VERT_HIGH_ACT,
.flag = FB_FLAG_RATIO_16_9,
.vmode = FB_VMODE_NONINTERLACED},
The recorders are expecting SMPTE standard inputs, and reject the current
ones. I can use either 3840x2160 or 4096x2160, and the refresh rate can be
either 60Hz or 59.94Hz.
I have tested the other modes available, and 1080p works fine at 60Hz. Both
4K modes work at 30Hz. It's when trying to set 4K @ 60Hz that the
granularity of the pixclock ends up being a problem (it would need to be
1683.5 for the math to work out the same as the other modes).
I attempted using cvt, cvt12, and gtf to generate modelines, but none of
them work either. I also used the source code from those programs to
attempt a brute-force method by generating as many modelines as I could
that end up within 0.0001% of the correct refresh rates (same accuracy as
the EDID's 1080p@60 mode, which is actually 60.00006Hz). That generated
1520 possibilities that followed the math rules for modelines, but none of
those worked either.
I've contacted the support departments for all of the hardware companies
involved, and none of them have been able to help.
I have verified that the system is outputting to HDMI with the settings I'm
using.
So, I'm looking for SMPTE standard compliant modelines for any of the
following: 3840x2160@60, 3840x2160@59.94, 4096x2160@60, or 4096x2160@59.94.
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