drm/i915: Disable GMBUS clock gating around GMBUS transfers on gen9+

Gen9+ need to disable GMBUS clock gating when doing multi part
transfers. Otherwise clock gating will kick in when GMBUS is in
the WAIT state and presumably that will corrupt the transfer.
This is documented as Display WA #0868.

Apparently older hardware doesn't allow clock gating in the WAIT
state and thus are unaffected by this problem.

v2: Limit the PCH w/a to gen9 and gen10 only (DK)
    Actually change it to check the PCH type instead since
    it's the PCH that actually contains the GMBUS hardware

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com> #v1
Link: https://patchwork.freedesktop.org/patch/msgid/20171221202432.17373-1-ville.syrjala@linux.intel.com

diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index fb05849eabab4c2375d7f4194e9e6a2a10959b7e..41285bec8fc03720ec2799bc6770f0dc46f7c211 100644 (file)
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -3859,6 +3859,9 @@ enum {
 #define   PWM2_GATING_DIS              (1 << 14)
 #define   PWM1_GATING_DIS              (1 << 13)
 
+#define GEN9_CLKGATE_DIS_4             _MMIO(0x4653C)
+#define   BXT_GMBUS_GATING_DIS         (1 << 14)
+
 #define _CLKGATE_DIS_PSL_A             0x46520
 #define _CLKGATE_DIS_PSL_B             0x46524
 #define _CLKGATE_DIS_PSL_C             0x46528
@@ -7557,6 +7560,7 @@ enum {
 #define FDI_RX_CHICKEN(pipe)   _MMIO_PIPE(pipe, _FDI_RXA_CHICKEN, _FDI_RXB_CHICKEN)
 
 #define SOUTH_DSPCLK_GATE_D    _MMIO(0xc2020)
+#define  PCH_GMBUSUNIT_CLOCK_GATE_DISABLE (1<<31)
 #define  PCH_DPLUNIT_CLOCK_GATE_DISABLE (1<<30)
 #define  PCH_DPLSUNIT_CLOCK_GATE_DISABLE (1<<29)
 #define  PCH_CPUNIT_CLOCK_GATE_DISABLE (1<<14)

diff --git a/drivers/gpu/drm/i915/intel_i2c.c b/drivers/gpu/drm/i915/intel_i2c.c
index a8c08994f505ee61a1fd9bf25f42e9a15014b522..ef9f91a0b0c9869caf1736e2d5fbaf77ab589560 100644 (file)
--- a/drivers/gpu/drm/i915/intel_i2c.c
+++ b/drivers/gpu/drm/i915/intel_i2c.c
@@ -142,6 +142,32 @@ static void pnv_gmbus_clock_gating(struct drm_i915_private *dev_priv,
        I915_WRITE(DSPCLK_GATE_D, val);
 }
 
+static void pch_gmbus_clock_gating(struct drm_i915_private *dev_priv,
+                                  bool enable)
+{
+       u32 val;
+
+       val = I915_READ(SOUTH_DSPCLK_GATE_D);
+       if (!enable)
+               val |= PCH_GMBUSUNIT_CLOCK_GATE_DISABLE;
+       else
+               val &= ~PCH_GMBUSUNIT_CLOCK_GATE_DISABLE;
+       I915_WRITE(SOUTH_DSPCLK_GATE_D, val);
+}
+
+static void bxt_gmbus_clock_gating(struct drm_i915_private *dev_priv,
+                                  bool enable)
+{
+       u32 val;
+
+       val = I915_READ(GEN9_CLKGATE_DIS_4);
+       if (!enable)
+               val |= BXT_GMBUS_GATING_DIS;
+       else
+               val &= ~BXT_GMBUS_GATING_DIS;
+       I915_WRITE(GEN9_CLKGATE_DIS_4, val);
+}
+
 static u32 get_reserved(struct intel_gmbus *bus)
 {
        struct drm_i915_private *dev_priv = bus->dev_priv;
@@ -484,6 +510,13 @@ do_gmbus_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs, int num)
        int i = 0, inc, try = 0;
        int ret = 0;
 
+       /* Display WA #0868: skl,bxt,kbl,cfl,glk,cnl */
+       if (IS_GEN9_LP(dev_priv))
+               bxt_gmbus_clock_gating(dev_priv, false);
+       else if (HAS_PCH_SPT(dev_priv) ||
+                HAS_PCH_KBP(dev_priv) || HAS_PCH_CNP(dev_priv))
+               pch_gmbus_clock_gating(dev_priv, false);
+
 retry:
        I915_WRITE_FW(GMBUS0, bus->reg0);
 
@@ -585,6 +618,13 @@ timeout:
        ret = -EAGAIN;
 
 out:
+       /* Display WA #0868: skl,bxt,kbl,cfl,glk,cnl */
+       if (IS_GEN9_LP(dev_priv))
+               bxt_gmbus_clock_gating(dev_priv, true);
+       else if (HAS_PCH_SPT(dev_priv) ||
+                HAS_PCH_KBP(dev_priv) || HAS_PCH_CNP(dev_priv))
+               pch_gmbus_clock_gating(dev_priv, true);
+
        return ret;
 }