Implement Daniel Stone's recommendation to not read registers to infer
the hardware's state.

v2: Read GAMMA_MODE register value at init (Matt Roper's comment)

v3: Read GAMMA_MODE register in intel_modeset_readout_hw_state along
    with other registers (Matt Roper's comment).

v4: Mask GAMMA_MODE register with interesting bits when reading

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin at intel.com>
Reviewed-by: Matt Roper <matthew.d.roper at intel.com>
---
 drivers/gpu/drm/i915/intel_color.c   | 7 +++++--
 drivers/gpu/drm/i915/intel_display.c | 3 +++
 drivers/gpu/drm/i915/intel_drv.h     | 3 +++
 3 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_color.c 
b/drivers/gpu/drm/i915/intel_color.c
index 35b7f62..16657eb 100644
--- a/drivers/gpu/drm/i915/intel_color.c
+++ b/drivers/gpu/drm/i915/intel_color.c
@@ -121,6 +121,8 @@ static void haswell_load_luts(struct drm_crtc *crtc)
        struct drm_device *dev = crtc->dev;
        struct drm_i915_private *dev_priv = dev->dev_private;
        struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
+       struct intel_crtc_state *intel_crtc_state =
+               to_intel_crtc_state(crtc->state);
        bool reenable_ips = false;

        /*
@@ -128,11 +130,12 @@ static void haswell_load_luts(struct drm_crtc *crtc)
         * GAMMA_MODE is configured for split gamma and IPS_CTL has IPS enabled.
         */
        if (IS_HASWELL(dev) && intel_crtc->config->ips_enabled &&
-           ((I915_READ(GAMMA_MODE(intel_crtc->pipe)) & GAMMA_MODE_MODE_MASK) ==
-            GAMMA_MODE_MODE_SPLIT)) {
+           (intel_crtc_state->gamma_mode == GAMMA_MODE_MODE_SPLIT)) {
                hsw_disable_ips(intel_crtc);
                reenable_ips = true;
        }
+
+       intel_crtc_state->gamma_mode = GAMMA_MODE_MODE_8BIT;
        I915_WRITE(GAMMA_MODE(intel_crtc->pipe), GAMMA_MODE_MODE_8BIT);

        i9xx_load_luts(crtc);
diff --git a/drivers/gpu/drm/i915/intel_display.c 
b/drivers/gpu/drm/i915/intel_display.c
index 66d6820..a5f57cd 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -9870,6 +9870,9 @@ static bool haswell_get_pipe_config(struct intel_crtc 
*crtc,

        intel_get_pipe_timings(crtc, pipe_config);

+       pipe_config->gamma_mode =
+               I915_READ(GAMMA_MODE(crtc->pipe)) & GAMMA_MODE_MODE_MASK;
+
        if (INTEL_INFO(dev)->gen >= 9) {
                skl_init_scalers(dev, crtc, pipe_config);
        }
diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index dc29816..d2855c7 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -518,6 +518,9 @@ struct intel_crtc_state {
                        struct skl_pipe_wm skl;
                } optimal;
        } wm;
+
+       /* Gamma mode programmed on the pipe */
+       uint32_t gamma_mode;
 };

 struct vlv_wm_state {
-- 
2.7.0

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