Commit 617f591f authored by Aaron Plattner's avatar Aaron Plattner
Browse files

modesetting: Only use GAMMA_LUT if its size is 1024

GAMMA_LUT sizes other than 1024 cause a crash during startup if the memcpy()
calls in xf86RandR12CrtcSetGamma() read past the end of the legacy X11 /
XVidMode gamma ramp.

This is a problem on Intel ICL / GEN11 platforms because they report a GAMMA_LUT
size of 262145. Since it's not clear that the modesetting driver will generate a
proper gamma ramp at that size even if xf86RandR12CrtcSetGamma() is fixed, just
disable use of GAMMA_LUT for sizes other than 1024 for now. This will cause the
modesetting driver to disable the CTM property and fall back to the legacy gamma

Signed-off-by: Aaron Plattner's avatarAaron Plattner <>
Fixes: #1193
Tested-by: Mark Herbert
parent e59e24c8
......@@ -2406,7 +2406,21 @@ drmmode_crtc_init(ScrnInfoPtr pScrn, drmmode_ptr drmmode, drmModeResPtr mode_res
drmmode_crtc->use_gamma_lut =
drmmode_crtc->props[DRMMODE_CRTC_GAMMA_LUT_SIZE].prop_id &&
drmmode_crtc->props[DRMMODE_CRTC_GAMMA_LUT_SIZE].value &&
/* Only use GAMMA_LUT if the size is 1024.
* Currently, the modesetting driver always passes a sigRGBbits value of
* 10 to xf86HandleColormaps. This causes it to create a RRCrtc gamma
* ramp of 1024 elements. If DRMMODE_CRTC_GAMMA_LUT_SIZE is larger than
* 1024 (for example on Intel GEN11, where it has a value of 262145)
* then xf86RandR12CrtcSetGamma will read past the end of the RRCrtc's
* gamma ramp when trying to copy it into the larger xf86Crtc gamma
* ramp.
* Since the larger GEN11 gamma ramp size hasn't been tested, just
* disable it for now. This will cause the modesetting driver to disable
* the CTM property and use the legacy DRM gamma ramp rather than the
* GAMMA_LUT property. */
drmmode_crtc->props[DRMMODE_CRTC_GAMMA_LUT_SIZE].value == 1024 &&
xf86ReturnOptValBool(drmmode->Options, OPTION_USE_GAMMA_LUT, TRUE);
if (drmmode_crtc->use_gamma_lut &&
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