Commit 66e5a5bb authored by Mario Kleiner's avatar Mario Kleiner Committed by Povilas Kanapickas
Browse files

modesetting: Enable GAMMA_LUT for lut's with up to 4096 slots.

A lut size of 4096 slots has been verified to work correctly,
as tested with amdgpu-kms. Intel Tigerlake Gen12 hw has a very
large GAMMA_LUT size of 262145 slots, but also issues with its
current GAMMA_LUT implementation, as of Linux 5.14.

Therefore we keep GAMMA_LUT off for large lut's. This currently
excludes Intel Icelake, Tigerlake and later.

This can be overriden via the "UseGammaLUT" boolean xorg.conf option
to force use of GAMMA_LUT on or off.

See following link for the Tigerlake situation:
drm/intel#3916 (comment 1085315)

Signed-off-by: Mario Kleiner's avatarMario Kleiner <>
parent 8b7f4d32
Pipeline #418809 passed with stages
in 4 minutes and 30 seconds
......@@ -2404,10 +2404,23 @@ drmmode_crtc_init(ScrnInfoPtr pScrn, drmmode_ptr drmmode, drmModeResPtr mode_res
xf86DrvMsgVerb(pScrn->scrnIndex, X_INFO, MS_LOGLEVEL_DEBUG,
"Allocated crtc nr. %d to this screen.\n", num);
drmmode_crtc->use_gamma_lut =
drmmode_crtc->props[DRMMODE_CRTC_GAMMA_LUT_SIZE].prop_id &&
drmmode_crtc->props[DRMMODE_CRTC_GAMMA_LUT_SIZE].value &&
xf86ReturnOptValBool(drmmode->Options, OPTION_USE_GAMMA_LUT, TRUE);
if (drmmode_crtc->props[DRMMODE_CRTC_GAMMA_LUT_SIZE].prop_id &&
drmmode_crtc->props[DRMMODE_CRTC_GAMMA_LUT_SIZE].value) {
* GAMMA_LUT property supported, and so far tested to be safe to use by
* default for lut sizes up to 4096 slots. Intel Tigerlake+ has some
* issues, and a large GAMMA_LUT with 262145 slots, so keep GAMMA_LUT
* off for large lut sizes by default for now.
drmmode_crtc->use_gamma_lut = drmmode_crtc->props[DRMMODE_CRTC_GAMMA_LUT_SIZE].value <= 4096;
/* Allow config override. */
drmmode_crtc->use_gamma_lut = xf86ReturnOptValBool(drmmode->Options,
} else {
drmmode_crtc->use_gamma_lut = FALSE;
if (drmmode_crtc->use_gamma_lut &&
drmmode_crtc->props[DRMMODE_CRTC_CTM].prop_id) {
......@@ -99,8 +99,8 @@ will assign xrandr outputs LVDS and VGA-0 to this instance of the driver.
.BI "Option \*qUseGammaLUT\*q \*q" boolean \*q
Enable or disable use of the GAMMA_LUT property, when available.
When enabled, this option allows the driver to use gamma ramps with more
entries, if supported by the kernel.
Default: on.
entries, if supported by the kernel. By default, GAMMA_LUT will be used for
kms drivers which are known to be safe for use of GAMMA_LUT.
@xservername@(@appmansuffix@), @xconfigfile@(@filemansuffix@), Xserver(@appmansuffix@),
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