[Nouveau] 240p mode can't get added with KMS, yet it works

[Pau López]

Hello,

I am using a GTX660, NVE6 (GK106) on arch linux.
kernel 3.16.3
xf86-video-nouveau 1.0.11

I am loading an EDID with kernel parameter
drm_kms_helper.edid_firmware= DVI-I-1:edid/320x240.bin
It doesn't apply the resolution. dmesg  prints:
  [   65.382880] [drm] Got external EDID base block and 0 extensions
from "edid/320x240vesa.bin" for connector "DVI-I-1"
  [   65.382890] [drm:drm_mode_debug_printmodeline] Modeline
56:"320x240" 59 6000 320 328 360 400 240 243 247 253 0x48 0x6
  [   65.382892] [drm:drm_mode_prune_invalid] Not using 320x240 mode 16

The last number is the status of the mode, wich acording to "drm_modes.h"
(https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/tree/include/drm/drm_modes.h?id=refs/tags/v3.16.3):
  MODE_CLOCK_LOW, /* clock required is too low */

I assume it means the dotclock, or pixel clock (6.000 MHz) is too low
for the GPU?

The thing is, on X i can use xrandr to set the same mode (or with the
same clock, or any clock i tried):
  xrandr --newmode "320x240" 6 320 328 360 400 240 243 247 253 +HSync -VSync
  xrandr --addmode DVI-I-1 320x240
  xrandr --output DVI-I-1 --mode 320x240

Also, the kernel parameter "video=DVI-I-1:320x240M" applies the mode,
but it doesn't get added.

I would be grateful to know:
What is the actual minimum dotclock supported by the video card?
Is it defined somewhere in the driver?
The validation of the display modes is handled by the driver, right?

I've attached dmesg and "edid-decode
/usr/lib/firmware/edid/320x240.bin" outputs, the EDID binary, and a
photo of the mode in action on X :)
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