In my hands it shows with Lehto's kernel at 800 and 1000 MHz (1000-800-250-ulv) and 1100 MHz (1100-800-250-ulv) but not 900/500/125 MHz (non-ulv), and with Titan's kernel (ulv) at 800 and 850 MHz but not at 810 MHz. So my guess is that the kernel likes MHz values divisible by 3 (i.e. 810 and 900) and warns for speeds which aren't a mutiple of 3.
WARNING: at arch/arm/mach-omap2/clock34xx.c:443 omap3_noncore_dpll_set_rate+0x28c/0x2dc() [ 80.165985] Modules linked in: vfat fat sd_mod scsi_mod iphb rfcomm panic_info_buff sco l2cap ext3 jbd omaplfb pvrsrvkm bridgedriver g_file_storage uinput board_rx51_camera omap_previewer_hack omap34xxcam_mod isp_mod iovmm videobuf_dma_sg videobuf_core omap3_iommu iommu2 iommu dspbridge ssi_mcsaab_imp cmt_speech phonet smc91x mii wl12xx omap_wdt omap_ssi mmc_block mac80211 crc7 tsc2005 omap_hsmmc nokia_av mmc_core hci_h4p bluetooth et8ek8 fmtx_si4713 lis302dl ad5820 videodev v4l1_compat compat_ioctl32 leds_lp5523 adp1653 tsl2563 smia_sensor smiaregs rtc_twl4030 v4l2_int_device rtc_core twl4030_wdt leds_twl4030_vibra led_class [ 80.166503] [<c003039c>] (dump_stack+0x0/0x14) from [<c00568d4>] (warn_on_slowpath+0x4c/0x68) [ 80.166625] [<c0056888>] (warn_on_slowpath+0x0/0x68) from [<c003d6d0>] (omap3_noncore_dpll_set_rate+0x28c/0x2dc) [ 80.166717] r6:c035a30c r5:60000113 r4:c035f2bc [ 80.166748] [<c003d444>] (omap3_noncore_dpll_set_rate+0x0/0x2dc) from [<c0035688>] (omap2_clk_set_rate+0x20/0x24) [ 80.166839] [<c0035668>] (omap2_clk_set_rate+0x0/0x24) from [<c0040e44>] (clk_set_rate+0x98/0x118) [ 80.166900] [<c0040dac>] (clk_set_rate+0x0/0x118) from [<c003dae4>] (program_opp+0xd0/0x18c) [ 80.166992] r7:00000004 r6:00000000 r5:00000020 r4:c03847b8 [ 80.167022] [<c003da14>] (program_opp+0x0/0x18c) from [<c003dca0>] (resource_set_opp_level+0x100/0x170) [ 80.167114] [<c003dba0>] (resource_set_opp_level+0x0/0x170) from [<c003dd54>] (set_opp+0x44/0xb4) [ 80.167175] r8:c035f58c r7:c035f718 r6:00000004 r5:c03847b8 r4:00000004 [ 80.167236] [<c003dd10>] (set_opp+0x0/0xb4) from [<c0049684>] (update_resource_level+0x5c/0x80) [ 80.167327] r5:c03847c8 r4:c035f544 [ 80.167358] [<c0049628>] (update_resource_level+0x0/0x80) from [<c00499a4>] (resource_request_locked+0x144/0x15c) [ 80.167449] r7:c035f718 r6:00000004 r5:c03847c8 r4:c035f544 [ 80.167480] [<c0049860>] (resource_request_locked+0x0/0x15c) from [<c003d9ec>] (set_freq+0x98/0xc0) [ 80.167572] r7:c035f718 r6:c035f6e8 r5:2faf0800 r4:c030f73a [ 80.167633] [<c003d954>] (set_freq+0x0/0xc0) from [<c0049684>] (update_resource_level+0x5c/0x80) [ 80.167694] r9:c037cbec r8:cf175280 r7:c0362348 r6:2faf0800 r5:c03854c0 [ 80.167755] r4:c035f58c [ 80.167785] [<c0049628>] (update_resource_level+0x0/0x80) from [<c00499a4>] (resource_request_locked+0x144/0x15c) [ 80.167846] r7:c0362348 r6:2faf0800 r5:c03854c0 r4:c035f58c [ 80.167907] [<c0049860>] (resource_request_locked+0x0/0x15c) from [<c00499f0>] (resource_request+0x34/0x4c) [ 80.167999] r7:c0362348 r6:2faf0800 r5:c03854c0 r4:c030f73a [ 80.168029] [<c00499bc>] (resource_request+0x0/0x4c) from [<c0049244>] (omap_pm_cpu_set_freq+0x34/0x44) [ 80.168121] r7:000927c0 r6:c035f6e8 r5:2faf0800 r4:00000005 [ 80.168182] [<c0049210>] (omap_pm_cpu_set_freq+0x0/0x44) from [<c00480b4>] (omap_target+0x60/0x78) [ 80.168243] [<c0048054>] (omap_target+0x0/0x78) from [<c01ea438>] (__cpufreq_driver_target+0x30/0x40) [ 80.168334] r7:00000000 r6:0003d090 r5:00000000 r4:c037cbec [ 80.168365] [<c01ea408>] (__cpufreq_driver_target+0x0/0x40) from [<c01ece14>] (do_dbs_timer+0x270/0x2d8) [ 80.168457] [<c01ecba4>] (do_dbs_timer+0x0/0x2d8) from [<c0068af4>] (run_workqueue+0xd4/0x198) [ 80.168548] [<c0068a20>] (run_workqueue+0x0/0x198) from [<c0069894>] (worker_thread+0xf0/0x104) [ 80.168609] r9:00000000 r8:00000000 r7:cf14ff40 r6:cf1b6000 r5:cf0f4d00 [ 80.168670] r4:cf1b7fb8 [ 80.168701] [<c00697a4>] (worker_thread+0x0/0x104) from [<c006cb0c>] (kthread+0x54/0x80) [ 80.168762] r7:00000000 r6:00000000 r5:c00697a4 r4:cf14ff40 [ 80.168823] [<c006cab8>] (kthread+0x0/0x80) from [<c0059a64>] (do_exit+0x0/0x7b4) [ 80.168884] r5:00000000 r4:00000000 [ 80.168914] ---[ end trace a249d49efdbc33bf ]---