Well quick recompilation on the newest tegra_next gives:
$ dmesg | grep Unusuall
[ 9.654098] tegradc tegradc.1: Unusuall display aspect ratio. You may encounter problems with base resolution
[ 9.665417] tegradc tegradc.1: Unusuall display aspect ratio. You may encounter problems with base resolution
[ 9.676755] tegradc tegradc.1: Unusuall display aspect ratio. You may encounter problems with base resolution
[ 9.688071] tegradc tegradc.1: Unusuall display aspect ratio. You may encounter problems with base resolution
[ 9.699391] tegradc tegradc.1: Unusuall display aspect ratio. You may encounter problems with base resolution
[ 9.710706] tegradc tegradc.1: Unusuall display aspect ratio. You may encounter problems with base resolution
But:
1920x540 is rejected:
[2223759.273] (II) TEGRA(0): Not using mode "1920x540" (unknown reason)
I thought that returning true will do the same trick as my patch does (but for all ratios), but it looks like it does not?