modesetting: Use GAMMA_LUT when available

If the kernel exposes GAMMA_LUT and GAMMA_LUT_SIZE properties and the size is
not what the server has pre-configured for the crtc, free the old gamma ramp
memory allocated by the server and replace it with new allocations of the
appropriate size.

In addition, when GAMMA_LUT is available, use drmModeCreatePropertyBlob() and
drmModeObjectSetProperty() to set the gamma ramp rather than using the legacy
drmModeCrtcSetGamma() function.

Add a new option "UseGammaLUT" to allow disabling this new behavior and falling
back to drmModeCrtcSetGamma() unconditionally.
Signed-off-by: Aaron Plattner <aplattner@nvidia.com>

hw/xfree86/drivers/modesetting/driver.c

@@ -140,6 +140,7 @@ static const OptionInfoRec Options[] = {
     {OPTION_DOUBLE_SHADOW, "DoubleShadow", OPTV_BOOLEAN, {0}, FALSE},
     {OPTION_ATOMIC, "Atomic", OPTV_BOOLEAN, {0}, FALSE},
     {OPTION_VARIABLE_REFRESH, "VariableRefresh", OPTV_BOOLEAN, {0}, FALSE},
+    {OPTION_USE_GAMMA_LUT, "UseGammaLUT", OPTV_BOOLEAN, {0}, FALSE},
     {-1, NULL, OPTV_NONE, {0}, FALSE}
 };
 

hw/xfree86/drivers/modesetting/driver.h

@@ -57,6 +57,7 @@ typedef enum {
     OPTION_DOUBLE_SHADOW,
     OPTION_ATOMIC,
     OPTION_VARIABLE_REFRESH,
+    OPTION_USE_GAMMA_LUT,
 } modesettingOpts;
 
 typedef struct

hw/xfree86/drivers/modesetting/drmmode_display.c

@@ -1669,6 +1669,35 @@ drmmode_show_cursor(xf86CrtcPtr crtc)
     return drmmode_set_cursor(crtc);
 }
 
+static void
+drmmode_set_gamma_lut(drmmode_crtc_private_ptr drmmode_crtc,
+                      uint16_t * red, uint16_t * green, uint16_t * blue,
+                      int size)
+{
+    drmmode_ptr drmmode = drmmode_crtc->drmmode;
+    drmmode_prop_info_ptr gamma_lut_info =
+        &drmmode_crtc->props[DRMMODE_CRTC_GAMMA_LUT];
+    const uint32_t crtc_id = drmmode_crtc->mode_crtc->crtc_id;
+    uint32_t blob_id;
+    struct drm_color_lut lut[size];
+
+    assert(gamma_lut_info->prop_id != 0);
+
+    for (int i = 0; i < size; i++) {
+        lut[i].red = red[i];
+        lut[i].green = green[i];
+        lut[i].blue = blue[i];
+    }
+
+    if (drmModeCreatePropertyBlob(drmmode->fd, lut, sizeof(lut), &blob_id))
+        return;
+
+    drmModeObjectSetProperty(drmmode->fd, crtc_id, DRM_MODE_OBJECT_CRTC,
+                             gamma_lut_info->prop_id, blob_id);
+
+    drmModeDestroyPropertyBlob(drmmode->fd, blob_id);
+}
+
 static void
 drmmode_crtc_gamma_set(xf86CrtcPtr crtc, uint16_t * red, uint16_t * green,
                        uint16_t * blue, int size)
@@ -1676,8 +1705,12 @@ drmmode_crtc_gamma_set(xf86CrtcPtr crtc, uint16_t * red, uint16_t * green,
     drmmode_crtc_private_ptr drmmode_crtc = crtc->driver_private;
     drmmode_ptr drmmode = drmmode_crtc->drmmode;
 
-    drmModeCrtcSetGamma(drmmode->fd, drmmode_crtc->mode_crtc->crtc_id,
-                        size, red, green, blue);
+    if (drmmode_crtc->use_gamma_lut) {
+        drmmode_set_gamma_lut(drmmode_crtc, red, green, blue, size);
+    } else {
+        drmModeCrtcSetGamma(drmmode->fd, drmmode_crtc->mode_crtc->crtc_id,
+                            size, red, green, blue);
+    }
 }
 
 static Bool
@@ -2266,6 +2299,8 @@ drmmode_crtc_init(ScrnInfoPtr pScrn, drmmode_ptr drmmode, drmModeResPtr mode_res
     static const drmmode_prop_info_rec crtc_props[] = {
         [DRMMODE_CRTC_ACTIVE] = { .name = "ACTIVE" },
         [DRMMODE_CRTC_MODE_ID] = { .name = "MODE_ID" },
+        [DRMMODE_CRTC_GAMMA_LUT] = { .name = "GAMMA_LUT" },
+        [DRMMODE_CRTC_GAMMA_LUT_SIZE] = { .name = "GAMMA_LUT_SIZE" },
     };
 
     crtc = xf86CrtcCreate(pScrn, &drmmode_crtc_funcs);
@@ -2302,6 +2337,39 @@ 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);
 
+    /* If the GAMMA_LUT property is available, replace the server's default
+     * gamma ramps with ones of the appropriate size. */
+    if (drmmode_crtc->props[DRMMODE_CRTC_GAMMA_LUT_SIZE].prop_id) {
+        Bool try_gamma_lut =
+            xf86ReturnOptValBool(drmmode->Options, OPTION_USE_GAMMA_LUT, TRUE);
+        uint64_t size = drmmode_crtc->props[DRMMODE_CRTC_GAMMA_LUT_SIZE].value;
+
+        if (try_gamma_lut && size != crtc->gamma_size) {
+            uint16_t *gamma = malloc(3 * size * sizeof(uint16_t));
+
+            if (gamma) {
+                free(crtc->gamma_red);
+
+                crtc->gamma_size = size;
+                crtc->gamma_red = gamma;
+                crtc->gamma_green = gamma + size;
+                crtc->gamma_blue = gamma + size * 2;
+
+                drmmode_crtc->use_gamma_lut = TRUE;
+
+                xf86DrvMsgVerb(pScrn->scrnIndex, X_INFO, MS_LOGLEVEL_DEBUG,
+                               "Gamma ramp set to %ld entries on CRTC %d\n",
+                               size, num);
+            } else {
+                xf86DrvMsg(pScrn->scrnIndex, X_WARNING,
+                           "Failed to allocate memory for %ld gamma ramp "
+                           "entries on CRTC %d. Falling back to legacy "
+                           "%d-entry mode.\n",
+                           size, num, crtc->gamma_size);
+            }
+        }
+    }
+
     return 1;
 }
 

hw/xfree86/drivers/modesetting/drmmode_display.h

@@ -67,6 +67,8 @@ enum drmmode_connector_property {
 enum drmmode_crtc_property {
     DRMMODE_CRTC_ACTIVE,
     DRMMODE_CRTC_MODE_ID,
+    DRMMODE_CRTC_GAMMA_LUT,
+    DRMMODE_CRTC_GAMMA_LUT_SIZE,
     DRMMODE_CRTC__COUNT
 };
 
@@ -199,6 +201,7 @@ typedef struct {
     Bool flipping_active;
 
     Bool vrr_enabled;
+    Bool use_gamma_lut;
 } drmmode_crtc_private_rec, *drmmode_crtc_private_ptr;
 
 typedef struct {

hw/xfree86/drivers/modesetting/modesetting.man

@@ -81,6 +81,12 @@ For example:
 Option \*qZaphodHeads\*q \*qLVDS,VGA-0\*q
 will assign xrandr outputs LVDS and VGA-0 to this instance of the driver.
 .TP
+.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.
+.TP
 .SH "SEE ALSO"
 @xservername@(@appmansuffix@), @xconfigfile@(@filemansuffix@), Xserver(@appmansuffix@),
 X(@miscmansuffix@)