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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:
https://gitlab.freedesktop.org/drm/intel/-/issues/3916#note_1085315

Signed-off-by: Mario Kleiner <mario.kleiner.de@gmail.com>
(cherry picked from commit 66e5a5bb12)
This commit is contained in:
Mario Kleiner 2021-10-01 07:42:01 +02:00 committed by Povilas Kanapickas
parent bc1327e6de
commit 0d0986bf3b
2 changed files with 19 additions and 6 deletions
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21
hw/xfree86/drivers/modesetting/drmmode_display.c
View File

@ -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,
OPTION_USE_GAMMA_LUT,
drmmode_crtc->use_gamma_lut);
} else {
drmmode_crtc->use_gamma_lut = FALSE;
}
if (drmmode_crtc->use_gamma_lut &&
drmmode_crtc->props[DRMMODE_CRTC_CTM].prop_id) {

4
hw/xfree86/drivers/modesetting/modesetting.man
View File

@ -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.
.TP
.SH "SEE ALSO"
@xservername@(@appmansuffix@), @xconfigfile@(@filemansuffix@), Xserver(@appmansuffix@),